Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005634 nucleus	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 to nucleus based on phylogenetic inference from multiple HSP70 orthologs across species. HSP70 family members are well documented to localize to the nucleus, particularly under stress conditions and during specific cell cycle stages. For HSPA2 specifically, the mouse ortholog (Hsp70-2/P17156) has been shown to associate with synaptonemal complexes in the nucleus of meiotic spermatocytes (PMID:8622925). HSPA2 was also detected in the human sperm nucleus by proteomics (PMID:21630459). The IBA annotation is well supported by phylogenetic evidence and consistent with known biology. Reason: HSP70 family members are known to localize to the nucleus. HSPA2 in particular is associated with synaptonemal complexes within the nucleus of meiotic spermatocytes (PMID:8622925), and was detected in the sperm nucleus proteome (PMID:21630459). The IBA annotation from phylogenetic inference is well supported. Supporting Evidence: PMID:8622925 We previously found that HSP70-2 is associated with synaptonemal complexes in the nucleus of meiotic spermatocytes from mice and hamsters.
GO:0005737 cytoplasm	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 to cytoplasm based on phylogenetic inference. HSP70 family members are predominantly cytoplasmic proteins. UniProt notes the subcellular location of HSPA2 as cytoplasm/cytoskeleton/spindle (UniProt P54652). Hageman et al. (PMID:21231916) expressed HSPA2 in cell culture and demonstrated cytoplasmic chaperone activities (luciferase refolding, polyQ aggregation suppression), confirming cytoplasmic localization. This is a well-supported core localization. Reason: HSPA2 is a cytoplasmic chaperone as demonstrated by functional assays in the cytoplasm (PMID:21231916) and consistent with the known biology of HSP70 family members. The IBA phylogenetic annotation is correct. Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase and on the suppression of aggregation of a non-foldable polyQ (polyglutamine)-expanded Huntingtin fragment
GO:0005886 plasma membrane	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: IBA annotation of HSPA2 to plasma membrane based on phylogenetic inference. Several HSP70 family members have been shown to localize to the plasma membrane and cell surface, particularly under stress conditions. For HSPA2, the mouse ortholog (P17156) has been annotated to cell surface (GO_REF:0000107, Ensembl Compara). UniProt notes that HSPA2 is a component of the CatSper complex (by similarity), which is a sperm cell surface ion channel complex. The IBA annotation is plausible but plasma membrane localization is not a core feature of HSPA2 function. Reason: Plasma membrane localization of HSP70 family members is documented but is not the primary site of HSPA2 function. The main functional localizations are cytoplasm/cytosol and nucleus (synaptonemal complex). Plasma membrane association may relate to its role in the CatSper complex in sperm or stress-related surface presentation.
GO:0016887 ATP hydrolysis activity	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 for ATP hydrolysis activity based on phylogenetic inference from HSP70 orthologs. ATP hydrolysis is the fundamental mechanistic step driving the HSP70 chaperone cycle. The N-terminal nucleotide-binding domain of HSPA2 (residues 2-389) binds and hydrolyzes ATP, and the crystal structure of the HSPA2 ATPase domain has been solved in complex with ADP and phosphate (PDB:3I33, PMID:20072699). UniProt describes the allosteric coupling between ATP hydrolysis and substrate binding (UniProt P54652). This is a core molecular function of HSPA2. Reason: ATP hydrolysis is the fundamental catalytic activity of all HSP70 family members, driving the chaperone cycle. The HSPA2 ATPase domain crystal structure confirms this activity (PDB:3I33). The IBA annotation is strongly supported. Supporting Evidence: PMID:21231916 HSPA6 has a functional substrate-binding domain and possesses intrinsic ATPase activity that is as high as that of the canonical HSPA1A when stimulated by J-proteins
GO:0031072 heat shock protein binding	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 for heat shock protein binding based on phylogenetic inference. HSP70 family members interact extensively with co-chaperones including HSP40/DNAJ proteins, HSPBP1, and BAG domain proteins. HSPA2 has been shown by IPI evidence to interact with HSPBP1 (Q9NZL4) in multiple studies (PMID:16189514, PMID:16713569, PMID:25416956, PMID:28514442, PMID:33961781, PMID:35271311, PMID:40205054). HSPA2 also interacts with BAG4 (O95429) and DNAJA3 (UniProt P54652). These interactions with co-chaperones are integral to the HSP70 chaperone cycle. Reason: HSP70 chaperones fundamentally depend on interactions with co-chaperones (HSP40/DNAJ, NEFs like HSPBP1 and BAG proteins) for their function. The extensive IPI evidence for HSPA2-HSPBP1 interaction across multiple studies validates this annotation. This is a core molecular function.
GO:0044183 protein folding chaperone	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 as a protein folding chaperone based on phylogenetic inference from HSP70 orthologs including DnaK. This is the central molecular function of HSPA2. Hageman et al. (PMID:21231916) directly demonstrated that HSPA2 has chaperone activity by showing it supports refolding of heat-denatured luciferase and suppresses aggregation of polyQ-expanded Huntingtin. UniProt describes HSPA2 as a "molecular chaperone implicated in a wide variety of cellular processes, including protection of the proteome from stress, folding and transport of newly synthesized polypeptides" (UniProt P54652). This is the core molecular function annotation for HSPA2. Reason: Protein folding chaperone activity is the core molecular function of HSPA2, directly demonstrated by in vitro assays (PMID:21231916) and consistent with the well-characterized HSP70 chaperone mechanism. The IBA annotation is strongly supported by both phylogenetic and experimental evidence. Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase and on the suppression of aggregation of a non-foldable polyQ (polyglutamine)-expanded Huntingtin fragment
GO:0005829 cytosol	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 to cytosol based on phylogenetic inference. HSPA2 is a cytosolic chaperone. This annotation is also supported by direct experimental evidence (IDA) from PMID:21231916, where HSPA2 was overexpressed and shown to function in the cytosol. The IBA annotation is consistent with the IDA evidence and with the known biology of HSP70 family members. Reason: Cytosol is the primary functional compartment for HSPA2 chaperone activity, supported by both phylogenetic inference and direct experimental evidence (PMID:21231916 IDA). The IBA annotation is correct.
GO:0042026 protein refolding	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation of HSPA2 for involvement in protein refolding based on phylogenetic inference from HSP70 orthologs. Protein refolding is a core biological process mediated by HSP70 chaperones. Hageman et al. (PMID:21231916) directly demonstrated HSPA2 supports refolding of heat-denatured luciferase, providing experimental confirmation. This IBA annotation is strongly supported. Reason: Protein refolding is a core function of HSP70 chaperones, directly demonstrated for HSPA2 by luciferase refolding assays (PMID:21231916). The IBA annotation is well supported by phylogenetic and experimental evidence. Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase
GO:0000166 nucleotide binding	IEA GO_REF:0000043	ACCEPT	Summary: IEA annotation of HSPA2 for nucleotide binding based on UniProtKB/Swiss-Prot keyword mapping (KW-0547 Nucleotide-binding). HSPA2 has a well-characterized nucleotide-binding domain (residues 2-389) with multiple ATP binding sites confirmed by crystal structure (PDB:3I33). This is a correct but overly general annotation; GO:0005524 "ATP binding" is more specific and already annotated. Nonetheless, nucleotide binding is technically correct as a parent term. Reason: Nucleotide binding is correct for HSPA2, which has an N-terminal nucleotide-binding domain confirmed by crystal structure. While broader than the more specific ATP binding annotation (GO:0005524), it is not incorrect as an IEA annotation derived from keyword mapping.
GO:0005524 ATP binding	IEA GO_REF:0000120	ACCEPT	Summary: IEA annotation of HSPA2 for ATP binding based on combined automated annotation using InterPro (IPR013126 HSP70 family) and UniProtKB keyword (KW-0067 ATP-binding). The crystal structure of HSPA2 NBD in complex with ADP and phosphate (PDB:3I33, PMID:20072699) directly confirms ATP binding. UniProt annotates multiple ATP binding sites at residues 13-16, 72, 205-207, 271-278, and 342-345 (UniProt P54652). This is a well-supported core molecular function. Reason: ATP binding is fundamental to HSPA2 function and is confirmed by crystal structure (PDB:3I33) and multiple annotated binding sites in the NBD domain. The IEA annotation is correct.
GO:0005819 spindle	IEA GO_REF:0000044	ACCEPT	Summary: IEA annotation of HSPA2 to spindle based on UniProtKB/Swiss-Prot subcellular location vocabulary mapping. UniProt records HSPA2 subcellular location as "Cytoplasm, cytoskeleton, spindle" based on similarity to mouse Hsp70-2 (P17156). The mouse ortholog co-localizes with SHCBP1L at the spindle during meiosis. This is consistent with the meiotic spindle localization annotated elsewhere (GO:0072687). The more specific term GO:0072687 "meiotic spindle" is preferable, but spindle is not wrong as a broader term. Reason: HSPA2 localizes to the meiotic spindle based on similarity data from the mouse ortholog (UniProt P17156). The broader term "spindle" is acceptable as an IEA annotation, though GO:0072687 "meiotic spindle" is more specific and also annotated.
GO:0006986 response to unfolded protein	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation of HSPA2 for response to unfolded protein based on ARBA machine learning. As a member of the HSP70 chaperone family, HSPA2 is involved in the cellular response to unfolded proteins. UniProt describes HSPA2 as a molecular chaperone involved in "protection of the proteome from stress" and "the re-folding of misfolded proteins" (UniProt P54652). HSPA2 is constitutively expressed but its role in proteostasis is consistent with involvement in unfolded protein response. Reason: HSPA2 is a molecular chaperone that assists in refolding of misfolded proteins and suppresses protein aggregation (PMID:21231916), which are key components of the response to unfolded protein. The IEA annotation is correct.
GO:0007283 spermatogenesis	IEA GO_REF:0000120	ACCEPT	Summary: IEA annotation of HSPA2 for involvement in spermatogenesis based on combined automated annotation using orthology to mouse Hsp70-2 (P17156) and UniProtKB keyword (KW-0744 Spermatogenesis). The mouse knockout study (PMID:8622925) directly demonstrated that Hsp70-2 disruption causes failed meiosis, germ cell apoptosis, and male infertility. HSPA2 is the human ortholog and is constitutively expressed at very high levels in testis (PMID:7829106). This is a core specialized function of HSPA2. Reason: Spermatogenesis is a core specialized function of HSPA2, demonstrated by mouse knockout studies showing male infertility (PMID:8622925) and supported by high testicular expression (PMID:7829106). The IEA annotation is strongly supported. Supporting Evidence: PMID:8622925 Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile. PMID:7829106 HSPA2 is constitutively expressed in most tissues, with very high levels in testis and skeletal muscle.
GO:0016887 ATP hydrolysis activity	IEA GO_REF:0000002	ACCEPT	Summary: IEA annotation of HSPA2 for ATP hydrolysis activity based on InterPro record (IPR013126 HSP70 family) to GO term mapping. This is a duplicate of the IBA annotation for the same term (GO:0016887). ATP hydrolysis is the core catalytic activity of the HSP70 ATPase domain. The crystal structure of the HSPA2 ATPase domain (PDB:3I33) confirms this activity. Duplicate annotations with different evidence codes are acceptable. Reason: ATP hydrolysis activity is the core catalytic function of HSPA2, confirmed by crystal structure of the ATPase domain (PDB:3I33). The IEA from InterPro is correct and consistent with the IBA annotation.
GO:0019899 enzyme binding	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: IEA annotation of HSPA2 for enzyme binding based on ARBA machine learning. HSPA2 interacts with METTL21A (HSPA-KMT), an enzyme that trimethylates Lys-564 of HSPA2 (PMID:23921388). This qualifies as enzyme binding. However, this is a somewhat uninformative term; the interaction with METTL21A is more accurately described as HSPA2 being a substrate of this methyltransferase rather than HSPA2 having "enzyme binding" as a core molecular function. As a chaperone, HSPA2 also interacts with numerous enzymes as clients. Reason: Enzyme binding is technically correct (HSPA2 interacts with METTL21A methyltransferase, PMID:23921388), but it is not an informative description of HSPA2 core function. As a chaperone, HSPA2 binds many proteins including enzymes as clients or regulatory partners.
GO:0030154 cell differentiation	IEA GO_REF:0000043	MARK AS OVER ANNOTATED	Summary: IEA annotation of HSPA2 for cell differentiation based on UniProtKB keyword mapping (KW-0221 Differentiation). This is a very broad term. The differentiation keyword in UniProt for HSPA2 presumably relates to its role in spermatogenesis, specifically spermatid differentiation and development. The more specific terms GO:0007283 "spermatogenesis" and GO:0007286 "spermatid development" are already annotated and are more informative. Cell differentiation is too generic to be useful for HSPA2. Reason: GO:0030154 "cell differentiation" is too broad and uninformative for HSPA2. The relevant differentiation context is spermatogenesis/spermatid development, which is already captured by more specific annotations (GO:0007283, GO:0007286). This general term adds no useful information.
GO:0042026 protein refolding	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation of HSPA2 for protein refolding based on ARBA machine learning. This is a duplicate of the IBA and IDA annotations for the same term. Protein refolding is a core function of HSPA2, directly demonstrated by luciferase refolding assays (PMID:21231916). The IEA annotation is correct and consistent with experimental evidence. Reason: Protein refolding is a core function of HSPA2, confirmed by experimental evidence (PMID:21231916 IDA) and phylogenetic inference (IBA). The IEA annotation is correct.
GO:0051082 unfolded protein binding	IEA GO_REF:0000117	MODIFY	Summary: GO:0051082 "unfolded protein binding" is being obsoleted (go-ontology#30962) because the term describes binding rather than the actual molecular activity. HSPA2 is a bona fide ATP-dependent foldase chaperone, not merely a passive binder of unfolded proteins. The IEA annotation via ARBA machine learning correctly identifies the chaperone-related function but uses the wrong term. UniProt describes HSPA2 as a "molecular chaperone implicated in a wide variety of cellular processes, including protection of the proteome from stress, folding and transport of newly synthesized polypeptides" (UniProt P54652). The correct replacement is GO:0044183 "protein folding chaperone", which already has an IBA annotation for this gene, further confirming the appropriateness of the replacement. Reason: GO:0051082 is being obsoleted per go-ontology#30962 because it conflates passive binding with active chaperone function. For HSP70 family members like HSPA2, the correct term is GO:0044183 "protein folding chaperone" (foldase), as the protein actively assists protein folding through ATP-dependent cycles. This IEA annotation should be replaced with the correct MF term. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:16189514 Towards a proteome-scale map of the human protein-protein in...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interaction with HSPBP1 (Q9NZL4) detected in Rual et al. (PMID:16189514), a proteome-scale yeast two-hybrid study of human protein-protein interactions. HSPBP1 is a known HSP70 co-chaperone/nucleotide exchange factor. The interaction between HSPA2 and HSPBP1 is functionally relevant and has been confirmed in multiple independent studies. However, "protein binding" is uninformative; this interaction is better captured by GO:0031072 "heat shock protein binding" (already annotated via IBA) or by the co-chaperone interaction context. Reason: The interaction with HSPBP1 (a co-chaperone/NEF) is real and confirmed across multiple studies, but GO:0005515 "protein binding" is uninformative. This interaction is already captured by the more specific GO:0031072 "heat shock protein binding" IBA annotation. Replace with the more specific term. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:16713569 A protein-protein interaction network for human inherited at...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interaction with HSPBP1 (Q9NZL4) detected in Lim et al. (PMID:16713569), a protein-protein interaction network study for inherited ataxias. This is another detection of the HSPA2-HSPBP1 co-chaperone interaction. As with the other HSPBP1 interaction entries, "protein binding" is uninformative and the interaction is better represented by GO:0031072 "heat shock protein binding." Reason: Same rationale as the PMID:16189514 entry. HSPA2-HSPBP1 interaction is a co-chaperone interaction better described by GO:0031072 "heat shock protein binding" rather than the generic GO:0005515. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:25036637 A quantitative chaperone interaction network reveals the arc...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interactions detected in Taipale et al. (PMID:25036637), a quantitative chaperone interaction network study. The GOA data shows interactions with BAG4 (O95429), HSF2 (Q03933), and Q96BE0. BAG4 is a BAG domain co-chaperone that acts as a nucleotide exchange factor for HSP70s. HSF2 is a heat shock transcription factor. These are functionally relevant interactions for a chaperone. However, "protein binding" remains uninformative; these interactions reflect chaperone-co-chaperone interactions or client binding. Reason: The interactions with BAG4 (co-chaperone) and HSF2 are real and functionally relevant from a chaperone network study, but "protein binding" is uninformative. The BAG4 interaction is better described by GO:0031072 "heat shock protein binding." Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interactions with TRIM38 (O00635) and HSPBP1 (Q9NZL4) detected in Rolland et al. (PMID:25416956), a proteome-scale interactome mapping study. The HSPBP1 interaction is a well-validated co-chaperone interaction. TRIM38 is an E3 ubiquitin ligase; its interaction with HSPA2 could relate to chaperone- mediated targeting of substrates for ubiquitination. "Protein binding" is too generic for these functionally informative interactions. Reason: Contains validated co-chaperone interaction (HSPBP1) and ubiquitin ligase interaction (TRIM38). GO:0005515 "protein binding" is uninformative; the HSPBP1 interaction is better captured by GO:0031072 "heat shock protein binding." Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:28514442 Architecture of the human interactome defines protein commun...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interaction with HSPBP1 (Q9NZL4) detected in Huttlin et al. (PMID:28514442), a study on the architecture of the human interactome. This is yet another independent confirmation of the HSPA2-HSPBP1 co-chaperone interaction. "Protein binding" is uninformative for this functionally well-characterized interaction. Reason: Another confirmation of HSPA2-HSPBP1 co-chaperone interaction. GO:0005515 is uninformative; better captured by GO:0031072. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interaction with TRIM38 (O00635) detected in Sahni et al. (PMID:31515488), a study on disruption of protein interactions by genetic variants. The HSPA2-TRIM38 interaction may relate to chaperone-assisted ubiquitination. "Protein binding" is uninformative. Reason: The TRIM38 interaction may reflect chaperone-ubiquitin ligase cooperation, but GO:0005515 "protein binding" is uninformative. A more specific term would be appropriate, but without detailed characterization of the functional consequence, the best replacement is GO:0031072 for the general HSP70 interaction context. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interaction with BAG4 (O95429) detected in Luck et al. (PMID:32296183), a reference map of the human binary protein interactome. BAG4 is a co-chaperone containing a BAG domain that functions as a nucleotide exchange factor for HSP70 proteins. This is a functionally relevant chaperone-co-chaperone interaction. "Protein binding" is uninformative. Reason: BAG4 is an HSP70 co-chaperone; this interaction is functionally relevant and better described by GO:0031072 "heat shock protein binding" rather than the generic GO:0005515. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on a large number of interactions detected in Mair et al. (PMID:32814053), an interactome mapping study focused on neurodegenerative disease proteins. The GOA data lists interactions with many partners including HTT (P42858), SSB, SOCS6, multiple zinc finger proteins, and others. Some of these (HTT) are likely chaperone-client interactions relevant to aggregation suppression, consistent with the role of HSPA2 in suppressing polyQ aggregation (PMID:21231916). However, many interactions from large-scale screens may be non-specific or represent transient chaperone-client contacts. "Protein binding" is uninformative. Reason: Large-scale interactome study detecting many HSPA2 interactions. Some (HTT, DNAJA3) are functionally relevant for chaperone biology. However, GO:0005515 "protein binding" is uninformative. The chaperone-client and chaperone-co-chaperone interactions are better captured by existing annotations (GO:0044183, GO:0031072). Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interactions with HSF2 (Q03933) and HSPBP1 (Q9NZL4) detected in Huttlin et al. (PMID:33961781), a dual proteome-scale network study. Both are functionally relevant interactions: HSPBP1 is a co-chaperone and HSF2 is a heat shock transcription factor that could be regulated by chaperone interactions. "Protein binding" is uninformative. Reason: Both interaction partners (HSPBP1 co-chaperone, HSF2 transcription factor) are functionally relevant. GO:0005515 is uninformative; these are better captured by GO:0031072. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:35271311 OpenCell: Endogenous tagging for the cartography of human ce...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interaction with HSPBP1 (Q9NZL4) detected in Cho et al. (PMID:35271311), the OpenCell endogenous tagging study. This is another independent confirmation of the HSPA2-HSPBP1 co-chaperone interaction using endogenous tagging, a method less prone to overexpression artifacts. "Protein binding" is uninformative. Reason: Another independent confirmation of HSPA2-HSPBP1 interaction using endogenous tagging. GO:0005515 is uninformative; better captured by GO:0031072. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func...	MODIFY	Summary: IPI annotation of HSPA2 for protein binding based on interactions with HSF2 (Q03933) and HSPBP1 (Q9NZL4) detected in Kim et al. (PMID:40205054), a multimodal cell mapping study. These are the same well-validated interaction partners seen across multiple studies. "Protein binding" is uninformative. Reason: Well-validated interactions with HSPBP1 and HSF2. GO:0005515 is uninformative; better captured by GO:0031072. Proposed replacements: heat shock protein binding
GO:0000795 synaptonemal complex	IEA GO_REF:0000107	ACCEPT	Summary: IEA annotation of HSPA2 to synaptonemal complex based on Ensembl Compara orthology transfer from mouse Hsp70-2 (P17156). The mouse knockout study (PMID:8622925) directly demonstrated that HSP70-2 is associated with synaptonemal complexes in meiotic spermatocytes: "We previously found that HSP70-2 is associated with synaptonemal complexes in the nucleus of meiotic spermatocytes from mice and hamsters. While synaptonemal complexes assembled in Hsp70-2 -/- spermatocytes, structural abnormalities became apparent in these cells by late prophase." This is a well-supported specialized localization for HSPA2 during male meiosis. Reason: Synaptonemal complex localization is directly demonstrated for the mouse ortholog Hsp70-2 in meiotic spermatocytes (PMID:8622925) and is a key aspect of the specialized meiotic function of HSPA2. The IEA transfer from mouse is well justified. Supporting Evidence: PMID:8622925 We previously found that HSP70-2 is associated with synaptonemal complexes in the nucleus of meiotic spermatocytes from mice and hamsters. While synaptonemal complexes assembled in Hsp70-2 -/- spermatocytes, structural abnormalities became apparent in these cells by late prophase
GO:0001673 male germ cell nucleus	IEA GO_REF:0000107	ACCEPT	Summary: IEA annotation of HSPA2 to male germ cell nucleus based on Ensembl Compara orthology transfer from mouse Hsp70-2 (P17156). The mouse ortholog has been demonstrated to localize within the nucleus of meiotic spermatocytes where it associates with synaptonemal complexes (PMID:8622925). HSPA2 was also detected in the human sperm nucleus proteome (PMID:21630459). This is a well-supported specialized localization. Reason: Male germ cell nucleus localization is strongly supported by the mouse knockout study showing association with synaptonemal complexes in spermatocyte nuclei (PMID:8622925) and by proteomics detection in human sperm nuclei (PMID:21630459). Supporting Evidence: PMID:8622925 HSP70-2 is associated with synaptonemal complexes in the nucleus of meiotic spermatocytes from mice and hamsters.
GO:0009986 cell surface	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: IEA annotation of HSPA2 to cell surface based on Ensembl Compara orthology transfer from mouse Hsp70-2 (P17156). HSP70 family members have been reported at the cell surface in various contexts, particularly in sperm cells where HSPA2 may be surface-exposed as part of the CatSper complex or other surface structures. This is consistent with the CatSper complex annotation and the plasma membrane IBA annotation. However, cell surface localization is not a core feature of HSPA2 function. Reason: Cell surface localization is plausible for HSPA2, particularly in sperm cells, but is not a core functional localization. The primary functional compartments are cytosol and nucleus (synaptonemal complex).
GO:0036128 CatSper complex	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: IEA annotation of HSPA2 as part of the CatSper complex based on Ensembl Compara orthology transfer from mouse Hsp70-2 (P17156). UniProt notes "Component of the CatSper complex" for HSPA2 (by similarity to mouse). CatSper is a sperm-specific calcium ion channel complex essential for sperm motility and male fertility. HSPA2 association with CatSper is consistent with its specialized role in spermatogenesis and sperm function. Reason: CatSper complex membership is supported by mouse ortholog data and UniProt annotation (by similarity). This is a specialized sperm function consistent with the spermatogenesis role, but is a secondary localization rather than a core molecular function annotation.
GO:0048156 tau protein binding	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: IEA annotation of HSPA2 for tau protein binding based on Ensembl Compara orthology transfer from rat Hspa2 (P14659). HSP70 family members, particularly HSPA8/Hsc70, have been shown to interact with tau and participate in its degradation through chaperone-mediated autophagy. However, this annotation is transferred from the rat ortholog and the tau binding evidence may be stronger for other HSP70 family members (particularly HSPA8). For HSPA2, tau binding would represent a general chaperone-client interaction rather than a specific function. Reason: Tau protein binding is likely a general chaperone-client interaction shared across HSP70 family members rather than a specific function of HSPA2. The annotation is transferred from rat and may be more relevant to HSPA8/Hsc70 which is the primary constitutive HSP70 in neurons. For HSPA2, which has a specialized testis/meiosis role, tau binding is not a core function.
GO:0051087 protein-folding chaperone binding	IEA GO_REF:0000107	ACCEPT	Summary: IEA annotation of HSPA2 for protein-folding chaperone binding based on Ensembl Compara orthology transfer from rat Hspa2 (P14659). HSP70 family members interact extensively with co-chaperones (DNAJ/HSP40, HSPBP1, BAG domain proteins, HOP/STIP1). HSPA2 has demonstrated interactions with HSPBP1 across multiple studies (PMID:16189514, PMID:16713569, PMID:25416956, PMID:28514442, PMID:33961781, PMID:35271311, PMID:40205054) and with BAG4 (PMID:25036637, PMID:32296183) and DNAJA3 (PMID:32814053). This is a well-supported function. Note this describes HSPA2 binding to other chaperones (HSPA2 as the subject), which is essentially the reciprocal of heat shock protein binding. Reason: HSPA2 binding to co-chaperones (HSPBP1, BAG4, DNAJA3) is extensively documented by IPI evidence across multiple studies. This is a core aspect of HSP70 function.
GO:0051861 glycolipid binding	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: IEA annotation of HSPA2 for glycolipid binding based on Ensembl Compara orthology transfer from mouse Hsp70-2 (P17156). This annotation likely relates to the reported interaction of HSP70 family members with sulfogalactosylglycerolipid (SGG/seminolipid) on the sperm surface, which has been proposed to play a role in sperm-egg interaction. This is a specialized sperm biology function. However, glycolipid binding is not a well-established molecular function of HSPA2 based on direct evidence and may represent an over-annotation based on indirect or limited evidence. Reason: Glycolipid binding is a specialized annotation transferred from the mouse ortholog that is based on limited evidence about HSP70-seminolipid interactions on sperm surfaces. This is not a well-characterized core molecular function of HSPA2 and likely represents over-annotation.
GO:0072687 meiotic spindle	IEA GO_REF:0000107	ACCEPT	Summary: IEA annotation of HSPA2 to meiotic spindle based on Ensembl Compara orthology transfer from mouse Hsp70-2 (P17156). UniProt notes that HSPA2 co-localizes with SHCBP1L at the spindle during meiosis (by similarity). This is consistent with the specialized meiotic function of HSPA2 in male germ cells. The more specific meiotic spindle term is appropriate given HSPA2's established role in male meiosis (PMID:8622925). Reason: Meiotic spindle localization is supported by mouse ortholog data showing HSPA2 co-localizes with SHCBP1L at the spindle during meiosis (UniProt, by similarity to P17156). This is consistent with HSPA2's essential role in male meiosis (PMID:8622925).
GO:0007283 spermatogenesis	ISS GO_REF:0000024	ACCEPT	Summary: ISS annotation of HSPA2 for spermatogenesis based on manual transfer from mouse ortholog Hsp70-2 (P17156). The mouse knockout study (PMID:8622925) definitively demonstrated that Hsp70-2 is required for spermatogenesis: male knockout mice lacked postmeiotic spermatids and mature sperm and were infertile. HSPA2 is the human ortholog with 98.2% amino acid identity (PMID:7829106). This is a core specialized function. Reason: Spermatogenesis is a core specialized function, directly demonstrated by mouse knockout (PMID:8622925). The ISS transfer from mouse is strongly justified by high sequence conservation (98.2% identity, PMID:7829106). Supporting Evidence: PMID:8622925 Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile.
GO:0072687 meiotic spindle	ISS GO_REF:0000024	ACCEPT	Summary: ISS annotation of HSPA2 to meiotic spindle based on manual transfer from mouse ortholog Hsp70-2 (P17156). UniProt notes HSPA2 co-localizes with SHCBP1L at the spindle during meiosis (by similarity). This is a duplicate of the IEA annotation for the same term. Both are supported by the mouse ortholog data. Reason: Meiotic spindle localization is well supported by mouse ortholog data (by similarity to P17156). The ISS annotation is correct and consistent with the IEA annotation.
GO:0009408 response to heat	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation of HSPA2 for response to heat based on manual transfer from orthologs by AgBase. HSPA2 is a member of the HSP70 family, which are classically involved in the heat shock response. However, HSPA2 is notably constitutively expressed rather than heat-inducible. The original characterization (PMID:7829106) describes HSPA2 as constitutively expressed. UniProt keywords include "Stress response" but HSPA2 is not a canonical heat-inducible HSP70 (unlike HSPA1A/HSPA6). While HSPA2 likely participates in protein quality control during heat stress as a constitutive chaperone, "response to heat" may be somewhat misleading for a constitutively expressed member. This is a non-core annotation. Reason: HSPA2 is constitutively expressed (PMID:7829106) rather than heat-inducible, distinguishing it from canonical heat-inducible HSP70s like HSPA1A. It may participate in heat stress response through its constitutive chaperone activity, but "response to heat" is not a core or distinguishing function of HSPA2. Supporting Evidence: PMID:7829106 HSPA2 is constitutively expressed in most tissues, with very high levels in testis and skeletal muscle.
GO:0009409 response to cold	ISS GO_REF:0000024	MARK AS OVER ANNOTATED	Summary: ISS annotation of HSPA2 for response to cold based on manual transfer from orthologs by AgBase. HSP70 family members can be induced by various stresses including cold. However, HSPA2 is constitutively expressed (PMID:7829106) and there is limited direct evidence for its specific involvement in cold stress response in humans. This annotation likely derives from studies of HSP70 orthologs in other organisms (e.g., fish) where cold stress induces HSP70 expression. For HSPA2, this is at best a peripheral function. Reason: HSPA2 is constitutively expressed (PMID:7829106) and there is no strong evidence for specific involvement in cold stress response. This annotation likely derives from studies in distantly related organisms where HSP70 induction by cold is documented, but this is not a core or well-established function of human HSPA2.
GO:0016020 membrane	HDA PMID:19946888 Defining the membrane proteome of NK cells.	KEEP AS NON CORE	Summary: HDA annotation of HSPA2 to membrane based on high-throughput proteomics of NK cell membranes (PMID:19946888). HSPA2 was detected in the membrane proteome of NK cells. HSP70 family members are known to associate with membranes, particularly under stress conditions, and have been detected on cell surfaces. However, "membrane" is a very broad cellular component term and membrane association is not a core localization of HSPA2. Reason: HSPA2 detection in the membrane proteome of NK cells is plausible but represents a non-core localization. The term "membrane" is very broad, and HSPA2's primary functional localization is cytosol and nucleus (synaptonemal complex in meiosis).
GO:0019899 enzyme binding	IPI PMID:23921388 Identification and characterization of a novel human methylt...	KEEP AS NON CORE	Summary: IPI annotation of HSPA2 for enzyme binding based on its interaction with METTL21A (Q8WXB1, also known as HSPA-KMT) demonstrated in Jakobsson et al. (PMID:23921388). METTL21A was identified as the methyltransferase responsible for trimethylation of Lys-564 in HSPA2 and other HSP70 family members. The interaction was demonstrated both in vitro and in vivo, and the K564A mutation abolished methylation. This is a real enzyme-substrate interaction where HSPA2 is the substrate. However, "enzyme binding" is relatively uninformative; the biologically informative aspect is that HSPA2 is a substrate of METTL21A methyltransferase. Reason: The interaction between HSPA2 and METTL21A (PMID:23921388) is real and well-characterized, but HSPA2 is the substrate rather than having enzyme binding as a core molecular function. This is a non-core annotation. Supporting Evidence: PMID:23921388 we identified the methyltransferase METTL21A as the enzyme responsible for trimethylation of a conserved lysine residue found in several human Hsp70 (HSPA) proteins
GO:0005829 cytosol	IDA PMID:21231916 The diverse members of the mammalian HSP70 machine show dist...	ACCEPT	Summary: IDA annotation of HSPA2 to cytosol based on Hageman et al. (PMID:21231916), who demonstrated cytosolic chaperone activities of HSPA2 including luciferase refolding and polyQ aggregation suppression. These functional assays were performed in the cytosol of cultured cells. This is direct experimental evidence for cytosolic localization and is consistent with the IBA annotation for the same term. Reason: Cytosol localization is directly demonstrated by functional chaperone assays (luciferase refolding, polyQ aggregation suppression) performed in the cytosol (PMID:21231916). This is a core localization for HSPA2. Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase and on the suppression of aggregation of a non-foldable polyQ (polyglutamine)-expanded Huntingtin fragment
GO:0042026 protein refolding	IDA PMID:21231916 The diverse members of the mammalian HSP70 machine show dist...	ACCEPT	Summary: IDA annotation of HSPA2 for protein refolding based on Hageman et al. (PMID:21231916), who directly demonstrated that HSPA2 overexpression supports refolding of heat-denatured luciferase. This is direct experimental evidence from a systematic comparison of all mammalian HSP70 family members. HSPA2 was shown to be competent for luciferase refolding, confirming its function as a protein refolding chaperone. Reason: Direct experimental evidence demonstrating HSPA2 supports luciferase refolding (PMID:21231916). This is a core biological process function of HSPA2 as an HSP70 chaperone. Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase
GO:0051082 unfolded protein binding	IDA PMID:21231916 The diverse members of the mammalian HSP70 machine show dist...	MODIFY	Summary: Hageman et al. (PMID:21231916) systematically compared the chaperone activities of mammalian HSP70 family members using functional assays for protein refolding and aggregation suppression. The study assessed HSPA2 and other HSPAs for "refolding of heat-denatured luciferase" and "suppression of aggregation of a non-foldable polyQ-expanded Huntingtin fragment." These are assays of active chaperone function (foldase activity), not merely passive binding to unfolded substrates. HSPA2 was shown to support luciferase refolding and suppress protein aggregation, demonstrating it functions as an ATP-dependent protein folding chaperone. The annotation as GO:0051082 "unfolded protein binding" underrepresents this activity; the correct term is GO:0044183 "protein folding chaperone." GO:0051082 is being obsoleted per go-ontology#30962. Reason: The experimental evidence from PMID:21231916 demonstrates active chaperone function (refolding of denatured luciferase, suppression of polyQ aggregation), which is GO:0044183 "protein folding chaperone" activity, not merely passive binding to unfolded proteins (GO:0051082). Furthermore, GO:0051082 is being obsoleted (go-ontology#30962) with GO:0044183 as the recommended replacement for foldase-type chaperones. HSPA2 already has an IBA annotation for GO:0044183, and the IDA evidence from this paper directly supports that term. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase and on the suppression of aggregation of a non-foldable polyQ (polyglutamine)-expanded Huntingtin fragment PMID:21231916 even within the highly sequence-conserved HSPA family, functional differentiation is larger than expected
GO:0090084 negative regulation of inclusion body assembly	IDA PMID:21231916 The diverse members of the mammalian HSP70 machine show dist...	ACCEPT	Summary: IDA annotation of HSPA2 for negative regulation of inclusion body assembly based on Hageman et al. (PMID:21231916), who demonstrated that HSPA2 overexpression suppresses aggregation of a polyQ-expanded Huntingtin fragment. This suppression of protein aggregation (inclusion body formation) is a direct consequence of HSPA2 chaperone activity. The annotation accurately describes the experimental observation that HSPA2 can prevent inclusion body formation by maintaining client proteins in a soluble state. Reason: Directly demonstrated by the polyQ aggregation suppression assay in PMID:21231916. Suppression of protein aggregation/inclusion body formation is a core chaperone function of HSPA2. This is a well-supported annotation. Supporting Evidence: PMID:21231916 we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase and on the suppression of aggregation of a non-foldable polyQ (polyglutamine)-expanded Huntingtin fragment
GO:0005634 nucleus	HDA PMID:21630459 Proteomic characterization of the human sperm nucleus.	ACCEPT	Summary: HDA annotation of HSPA2 to nucleus based on proteomic characterization of the human sperm nucleus (PMID:21630459). HSPA2 was identified as a component of the sperm nucleus proteome by high-throughput mass spectrometry. This is consistent with HSPA2's known role in spermatogenesis and its association with synaptonemal complexes in the nucleus of meiotic spermatocytes (PMID:8622925). Nuclear localization is a well-supported aspect of HSPA2 biology. Reason: HSPA2 was detected in the human sperm nucleus proteome (PMID:21630459), consistent with its role in meiotic spermatocyte nuclei where it associates with synaptonemal complexes (PMID:8622925). Nuclear localization is supported by multiple independent lines of evidence.
GO:0072562 blood microparticle	HDA PMID:22516433 Proteomic analysis of microvesicles from plasma of healthy d...	KEEP AS NON CORE	Summary: HDA annotation of HSPA2 to blood microparticle based on proteomic analysis of plasma microvesicles (PMID:22516433). HSP70 proteins are commonly detected in extracellular vesicles and blood microparticles, likely reflecting their abundance and their role in extracellular signaling or stress response. Detection in blood microparticles is not a core functional localization for HSPA2. Reason: Detection in blood microparticles is a common finding for abundant intracellular proteins in proteomics studies. This is not a core functional localization for HSPA2 but may reflect real biology (extracellular chaperone function or vesicular secretion).
GO:0070062 extracellular exosome	HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos...	KEEP AS NON CORE	Summary: HDA annotation of HSPA2 to extracellular exosome based on large-scale proteomics of urinary exosomes (PMID:19056867). HSP70 family members are among the most commonly detected proteins in exosome proteomics studies. While this may reflect real biology (HSP70s have roles in exosome biogenesis and can be secreted), it is not a core functional localization for HSPA2. Reason: HSP70 family members are commonly detected in exosome proteomics. While potentially real, extracellular exosome localization is not a core functional localization for HSPA2, whose primary functions are in cytosolic protein folding and meiotic spermatocyte biology.
GO:0036128 CatSper complex	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ISS annotation of HSPA2 as part of the CatSper complex based on manual transfer from mouse ortholog Hsp70-2 (P17156). UniProt states "Component of the CatSper complex" for HSPA2 (by similarity). CatSper is a sperm-specific calcium channel complex essential for sperm motility and hyperactivation. HSPA2 association with CatSper is consistent with its specialized role in spermatogenesis and sperm function. This duplicates the IEA annotation for the same term. Reason: CatSper complex membership is supported by mouse ortholog data and UniProt annotation. This is a specialized sperm function annotation that is consistent with HSPA2's role in spermatogenesis but is a secondary aspect of its biology.
GO:0006986 response to unfolded protein	TAS PMID:7829106 Cloning, sequencing, and mapping of the human chromosome 14 ...	ACCEPT	Summary: TAS annotation of HSPA2 for response to unfolded protein based on Bonnycastle et al. (PMID:7829106), which cloned and characterized the HSPA2 gene. The paper describes HSPA2 as a member of the HSP70 family and notes its constitutive expression pattern. While the paper does not directly demonstrate response to unfolded protein, it characterizes HSPA2 as an HSP70 gene family member, and HSP70 proteins are fundamentally involved in the unfolded protein response. The TAS evidence code is appropriate for this inference based on family membership. Reason: HSPA2 is an HSP70 family member (PMID:7829106) and involvement in response to unfolded protein is a fundamental function of this family. The TAS annotation is appropriate given the well-established role of HSP70 chaperones in proteostasis. Supporting Evidence: PMID:7829106 A genomic clone for the human heat shock protein (HSP) 70 gene located on chromosome 14 was isolated and sequenced. The gene, designated HSPA2, has a single open reading frame of 1917 bp that encodes a 639-amino acid protein
GO:0051082 unfolded protein binding	TAS PMID:3037489 Structure and expression of a human gene coding for a 71 kd ...	MODIFY	Summary: PMID:3037489 (Dworniczak and Mirault, 1987) describes the structure and expression of a human gene coding for a 71 kDa heat shock cognate protein. The paper characterizes an hsc70 gene (likely HSPA8/HSC70, not HSPA2) as encoding a protein "very likely to be identical to a clathrin uncoating ATPase recently identified as a member of the hsp70-like protein family." This TAS annotation to HSPA2 appears to have been made based on the general understanding that HSP70 family members bind unfolded proteins, but the paper actually describes HSPA8, not HSPA2 specifically. Regardless of the attribution, GO:0051082 is being obsoleted (go-ontology#30962) and the appropriate replacement for HSP70 foldase-type chaperones is GO:0044183 "protein folding chaperone." HSPA2, like other HSP70 members, functions as an ATP-dependent foldase. Reason: GO:0051082 is being obsoleted (go-ontology#30962). The cited paper (PMID:3037489) describes a cognate hsc70 gene that may actually correspond to HSPA8 rather than HSPA2. Nonetheless, HSPA2 is a well-established HSP70 family member with documented foldase chaperone activity (PMID:21231916). The correct replacement term is GO:0044183 "protein folding chaperone", reflecting the active ATP-dependent protein folding function of HSP70 family members. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:3037489 In all eukaryotes examined so far, hsp70 gene families include cognate genes (hsc70) encoding proteins of about 70 Kd which are expressed constitutively during normal growth and development PMID:3037489 The latter is very likely to be identical to a clathrin uncoating ATPase recently identified as a member of the hsp70-like protein family
GO:0007140 male meiotic nuclear division	TAS PMID:8622925 Targeted gene disruption of Hsp70-2 results in failed meiosi...	ACCEPT	Summary: TAS annotation of HSPA2 for male meiotic nuclear division based on Dix et al. (PMID:8622925). This landmark paper demonstrated that targeted disruption of the mouse Hsp70-2 gene resulted in failed meiosis in male germ cells. Knockout males "lacked postmeiotic spermatids and mature sperm" and "development rarely progressed to the meiotic divisions." The study concluded that "HSP70-2 participates in synaptonemal complex function during meiosis in male germ cells." This is a core specialized function of HSPA2. Reason: Male meiotic nuclear division is a core specialized function of HSPA2, directly demonstrated by the mouse knockout study where loss of Hsp70-2 prevented meiotic progression (PMID:8622925). This is among the most well-supported annotations for HSPA2. Supporting Evidence: PMID:8622925 Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile. PMID:8622925 These results suggest that HSP70-2 participates in synaptonemal complex function during meiosis in male germ cells and is linked to mechanisms that inhibit apoptosis.
GO:0007286 spermatid development	TAS PMID:8622925 Targeted gene disruption of Hsp70-2 results in failed meiosi...	ACCEPT	Summary: TAS annotation of HSPA2 for spermatid development based on Dix et al. (PMID:8622925). The mouse knockout study showed that Hsp70-2 -/- males "lacked postmeiotic spermatids and mature sperm." This indicates that HSPA2 is required for the meiotic progression that precedes spermatid formation. However, the study shows that meiosis fails before spermatids are formed, so the absence of spermatids is an indirect consequence of failed meiosis rather than a direct role in spermatid development per se. The annotation is still appropriate under TAS evidence as a reasonable inference from the knockout phenotype. Reason: Spermatid development failure is a consequence of HSPA2/Hsp70-2 loss (PMID:8622925). While the primary defect is in meiotic progression, the resulting absence of spermatids means HSPA2 is required for this process. The TAS evidence code is appropriate for this inference. Supporting Evidence: PMID:8622925 Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile. However, neither meiosis nor fertility was affected in female Hsp70-2 -/- mice.

Core Functions

ATP-dependent protein folding chaperone that assists in refolding of heat-denatured proteins and suppresses aggregation of misfolded proteins (including polyQ-expanded substrates) in the cytosol, through cycles of ATP binding, hydrolysis, and ADP release mediated by J-domain and nucleotide exchange factor co-chaperones. The interaction network includes DNAJB12, STIP1, HSPBP1, HSPA1A, HSPA8, and HSP90AA1 (DOI:10.62347/cwpe7813). HSPA2 is also an extracellular vesicle (EV)- associated protein; proteotoxic stress can redistribute HSPA2 from intracellular pools to EVs (DOI:10.1038/s41598-023-31962-5). This provides a biological route for HSPA2 detection in biofluids and potential roles in intercellular communication.

Molecular Function:

protein folding chaperone

Directly Involved In:

protein refolding negative regulation of inclusion body assembly response to unfolded protein

Cellular Locations:

cytosol nucleus

Supporting Evidence:

PMID:21231916
we assessed the effect of overexpression of each of these HSPs on refolding of heat-denatured luciferase and on the suppression of aggregation of a non-foldable polyQ (polyglutamine)-expanded Huntingtin fragment

Essential chaperone for male meiosis and spermatogenesis. Associates with synaptonemal complexes during meiotic prophase and localizes to the meiotic spindle, where it is required for meiotic progression. Loss of the mouse ortholog Hsp70-2 causes failed meiosis, germ cell apoptosis, and male infertility. HSPA2 also supports post-meiotic sperm remodeling, including cytoplasmic extrusion and plasma membrane remodeling required for zona pellucida binding competence, with reported roles in enabling surface relocation of proteins needed for oocyte zona interaction during capacitation (DOI:10.3390/ijms23126497). Quantitative enrichment of HSPA2-positive cells in HA-bound sperm (68.9% vs 28.6% uncapacitated; DOI:10.1007/s43032-022-01031-9) connects HSPA2 with sperm functional maturity. HSPA2 interacts with SHCBP1L to support spindle integrity during male meiosis (DOI:10.62347/cwpe7813). Seminal plasma HSPA2 is a promising non-invasive biomarker for stratification of non-obstructive azoospermia, with 7.3-fold higher abundance in healthy controls vs Sertoli cell-only phenotype (DOI:10.3389/fendo.2024.1327800).

Molecular Function:

protein folding chaperone

Directly Involved In:

male meiotic nuclear division spermatogenesis spermatid development

Cellular Locations:

synaptonemal complex meiotic spindle male germ cell nucleus

Supporting Evidence:

PMID:8622925
Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile.
PMID:8622925
These results suggest that HSP70-2 participates in synaptonemal complex function during meiosis in male germ cells and is linked to mechanisms that inhibit apoptosis.
PMID:7829106
HSPA2 is constitutively expressed in most tissues, with very high levels in testis and skeletal muscle.

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:16189514

Towards a proteome-scale map of the human protein-protein interaction network.

PMID:16713569

A protein-protein interaction network for human inherited ataxias and disorders of Purkinje cell degeneration.

PMID:19056867

Large-scale proteomics and phosphoproteomics of urinary exosomes.

PMID:19946888

Defining the membrane proteome of NK cells.

PMID:21231916

The diverse members of the mammalian HSP70 machine show distinct chaperone-like activities.

PMID:21630459

Proteomic characterization of the human sperm nucleus.

PMID:22516433

Proteomic analysis of microvesicles from plasma of healthy donors reveals high individual variability.

PMID:23921388

Identification and characterization of a novel human methyltransferase modulating Hsp70 protein function through lysine methylation.

PMID:25036637

A quantitative chaperone interaction network reveals the architecture of cellular protein homeostasis pathways.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:28514442

Architecture of the human interactome defines protein communities and disease networks.

PMID:3037489

Structure and expression of a human gene coding for a 71 kd heat shock 'cognate' protein.

PMID:31515488

Extensive disruption of protein interactions by genetic variants across the allele frequency spectrum in human populations.

PMID:32296183

A reference map of the human binary protein interactome.

PMID:32814053

Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains.

PMID:33961781

Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.

PMID:35271311

OpenCell: Endogenous tagging for the cartography of human cellular organization.

PMID:40205054

Multimodal cell maps as a foundation for structural and functional genomics.

PMID:7829106

Cloning, sequencing, and mapping of the human chromosome 14 heat shock protein gene (HSPA2).

PMID:8622925

Targeted gene disruption of Hsp70-2 results in failed meiosis, germ cell apoptosis, and male infertility.

DOI:10.1038/s41598-023-31962-5

Heat shock protein A2 is a novel extracellular vesicle-associated protein

Demonstrates HSPA2 is an EV-associated protein. Proteotoxic stress (proteasome inhibition with bortezomib) shifts HSPA2 from intracellular pools to extracellular release in EVs. Validated using CRISPR/Cas9 HSPA2 knockout pools and GFP-HSPA2 overexpression. EV mean size approximately 105.6 nm.

DOI:10.3390/ijms23126497

Targeted Analysis of HSP70 Isoforms in Human Spermatozoa in the Context of Capacitation and Motility

HSPA2 supports spermatogenesis and post-meiotic sperm remodeling, including cytoplasmic extrusion and plasma membrane remodeling required for zona pellucida binding competence. Roles in enabling surface relocation of proteins needed for oocyte zona interaction during capacitation.

DOI:10.1007/s43032-022-01031-9

Molecular Chaperone HSPA2 Distribution During Hyaluronic Acid Selection in Human Sperm

Quantified HSPA2 in human sperm (16 donors, approximately 19,200 sperm assessed). HA-bound sperm showed 68.9% HSPA2 positivity vs 28.6% uncapacitated and 22.9% capacitated (p<0.001). HA-bound sperm fraction was 21.4 plus/minus 7.4%.

DOI:10.3389/fendo.2024.1327800

Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men

Among 917 quantified proteins in seminal plasma proteomics, HSPA2 was more abundant in healthy controls than Sertoli cell-only phenotype (fold-change HC/SCO = 7.31, adjusted p=0.0217). Identifies HSPA2 as a promising non-invasive biomarker for spermatogenic function.

DOI:10.1093/cvr/cvae181

The diabetic myocardial transcriptome reveals Erbb3 and Hspa2 as novel biomarkers of incident heart failure

GTEx analysis (425 RA and 428 LV samples) showed diabetes associated with higher Hspa2 expression in LV myocardium. Higher circulating HSPA2 (highest quartile) was associated with impaired LV contractility, higher LV mass, and increased incident heart failure and cardiovascular death.

DOI:10.62347/cwpe7813

Bioinformatics analysis and alternative polyadenylation in Heat Shock Proteins 70 (HSP70) family members

Lists HSPA2-associated interactors including DNAJB12, STIP1, HSPBP1, HSPA1A, HSPA8, HSP90AA1. Notes HSPA2 role in spermatogenesis and proposed interaction with SHCBP1L to support spindle integrity during male meiosis.

📚 Additional Documentation

Deep Research Falcon

(HSPA2-deep-research-falcon.md)

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gene_id: HSPA2
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shock 70 kDa protein 2; AltName: Full=Heat shock protein family A member 2;'
gene_info: Name=HSPA2;
organism_full: Homo sapiens (Human).
protein_family: Belongs to the heat shock protein 70 family. .
protein_domains: ATPase_NBD. (IPR043129); Heat_shock_70_CS. (IPR018181); HSP70_C_sf.
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Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

UniProt Accession: P54652
Protein Description: RecName: Full=Heat shock-related 70 kDa protein 2; Short=Heat shock 70 kDa protein 2; AltName: Full=Heat shock protein family A member 2;
Gene Information: Name=HSPA2;
Organism (full): Homo sapiens (Human).
Protein Family: Belongs to the heat shock protein 70 family. .
Key Domains: ATPase_NBD. (IPR043129); Heat_shock_70_CS. (IPR018181); HSP70_C_sf. (IPR029048); HSP70_peptide-bd_sf. (IPR029047); Hsp_70_fam. (IPR013126)

MANDATORY VERIFICATION STEPS:

Check if the gene symbol "HSPA2" matches the protein description above
Verify the organism is correct: Homo sapiens (Human).
Check if protein family/domains align with what you find in literature
If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'HSPA2' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene HSPA2 (gene ID: HSPA2, UniProt: P54652) in human.

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Output

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

UniProt Accession: P54652
Protein Description: RecName: Full=Heat shock-related 70 kDa protein 2; Short=Heat shock 70 kDa protein 2; AltName: Full=Heat shock protein family A member 2;
Gene Information: Name=HSPA2;
Organism (full): Homo sapiens (Human).
Protein Family: Belongs to the heat shock protein 70 family. .
Key Domains: ATPase_NBD. (IPR043129); Heat_shock_70_CS. (IPR018181); HSP70_C_sf. (IPR029048); HSP70_peptide-bd_sf. (IPR029047); Hsp_70_fam. (IPR013126)

MANDATORY VERIFICATION STEPS:

Check if the gene symbol "HSPA2" matches the protein description above
Verify the organism is correct: Homo sapiens (Human).
Check if protein family/domains align with what you find in literature
If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Please provide a comprehensive research report on the gene HSPA2 (gene ID: HSPA2, UniProt: P54652) in human.

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Title: Functional Annotation Research Report — Human HSPA2 (UniProt P54652)

Target verification (gene/protein identity)

HSPA2 (UniProt accession P54652) encodes “Heat shock-related 70 kDa protein 2” (also referred to as “Hsp70-2”), a member of the HSPA/HSP70 family of molecular chaperones in Homo sapiens. Its family/domain architecture is consistent with canonical HSP70s, with an N-terminal nucleotide-binding domain (NBD) that has ATPase activity and a C-terminal substrate-binding domain (SBD) that binds client polypeptides. This domain organization is described in recent primary literature focused on HSPA2-specific biology, supporting that the literature cited here refers to the correct human protein (sojka2023heatshockprotein pages 1-2).

Key concepts and definitions (current understanding)

2.1. What HSPA2 is (molecular chaperone definition)

HSPA2 is a 70-kDa HSP70-family molecular chaperone. In current mechanistic understanding, HSP70-family proteins operate through ATP-dependent cycles: the NBD binds/hydrolyzes ATP, and allosteric coupling to the SBD regulates binding and release of unfolded or partially folded client proteins. In a functional definition used in recent HSPA2-focused work, HSPA/HSP70 proteins support folding/refolding of proteins, prevent aggregation, and can target damaged proteins for degradation (including via ubiquitin–proteasome system or chaperone-mediated autophagy pathways) (sojka2023heatshockprotein pages 1-2).

2.2. Broad functional categories relevant to functional annotation

Based on recent HSPA2-focused experimental and synthesis literature, HSPA2 is best annotated as:

• ATP-dependent molecular chaperone (protein folding/refolding; proteostasis) (sojka2023heatshockprotein pages 1-2)
• Germ-cell enriched chaperone linked to spermatogenesis and sperm functional maturation (grassi2022targetedanalysisof pages 1-2)
• Protein that can localize outside the cytosol, including association with extracellular vesicles (EVs), implying roles in extracellular communication/biomarker biology (sojka2023heatshockprotein pages 9-10)

2.3. Interaction partners / co-chaperone systems (conceptual context)

HSP70 function is typically modulated by co-chaperones (e.g., J-domain proteins/DNAJs) and adapter proteins that regulate ATPase cycling and client transfer. A 2024 synthesis/bioinformatic analysis lists HSPA2-associated or network-linked proteins consistent with co-chaperone/interactome logic, including DNAJ family members and other HSPs/cofactors (e.g., DNAJB12, STIP1, HSPBP1, HSPA1A, HSPA8, HSP90AA1), and additionally notes HSPA2’s role in spermatogenesis and a proposed interaction with SHCBP1L to support spindle integrity during male meiosis (shriya2024bioinformaticsanalysisand pages 4-6). While such lists contain inference and require experimental validation in each tissue context, they help define plausible HSPA2 pathway connectivity for annotation purposes (shriya2024bioinformaticsanalysisand pages 4-6).

Molecular function, pathways, and subcellular localization (with evidence)

3.1. Core molecular function (proteostasis; ATPase-driven chaperone cycle)

HSPA2 is an HSP70-family chaperone with the expected NBD ATPase and SBD client-binding architecture, supporting a primary function in ATP-dependent folding/refolding and protein quality control (sojka2023heatshockprotein pages 1-2). In functional annotation terms, this places HSPA2 in proteostasis pathways and chaperone-mediated folding networks (sojka2023heatshockprotein pages 1-2).

3.2. Subcellular localization — intracellular, surface, and extracellular vesicles

3.2.1. Cytosolic/“intracellular” role

HSPA2 is discussed in the context of canonical intracellular HSP70 chaperoning and proteostasis control (sojka2023heatshockprotein pages 1-2). In sperm, HSPA2 has been reported with diverse intracellular regional patterns (head/acrosomal/post-acrosomal/neck/tail), and its redistribution during capacitation has been debated (grassi2022targetedanalysisof pages 1-2).

3.2.2. Extracellular vesicle association (key 2023 development)

A major recent development is direct experimental evidence that HSPA2 is an extracellular vesicle (EV)-associated protein. Sojka et al. (Scientific Reports; publication date March 2023; URL https://doi.org/10.1038/s41598-023-31962-5) show that proteotoxic stress (e.g., proteasome inhibition) can shift HSPA2 from intracellular pools to extracellular release in EVs, and that EV-associated HSPA2 is also detectable from non-stressed cancer and normal cells (sojka2023heatshockprotein pages 2-3, sojka2023heatshockprotein pages 3-5). This work supports annotating HSPA2 not only as a cytosolic chaperone but also as a protein present in the extracellular compartment via EVs (sojka2023heatshockprotein pages 9-10).

Quantitative EV metrics under proteotoxic stress reported by Sojka et al. include: bortezomib (32 nM) increasing extracellular HSPA2 and nearly doubling EV number, with EV mean size ~105.6 ± 0.6 nm and mode ~92.0 ± 5.7 nm (sojka2023heatshockprotein pages 3-5). Antibody specificity controls included CRISPR/Cas9 HSPA2 knockout pools and GFP–HSPA2 overexpression to confirm EV association of HSPA2 (sojka2023heatshockprotein pages 3-5).

3.2.3. Plasma membrane exposure / extracellular HSP70 context

Although not HSPA2-exclusive, the extracellular HSP70 literature indicates that HSP70-family members can appear at the plasma membrane and/or be released in soluble or EV-associated form, with immunomodulatory consequences in cancer contexts. HSPA2 is specifically named among HSP70 family members found on plasma membrane in the cancer extracellular HSP70 review context (April 2024; Frontiers in Oncology; URL https://doi.org/10.3389/fonc.2024.1388999) (sojka2023heatshockprotein pages 9-10).

3.3. Biological processes — male germline and sperm function

3.3.1. Spermatogenesis and sperm functional maturation

A 2022 targeted analysis of HSP70 isoforms in human sperm summarizes the prevailing model that HSPA2 supports spermatogenesis (notably spermatocyte expression supporting meiosis) and post-meiotic sperm remodeling, including cytoplasmic extrusion and plasma membrane remodeling required for zona pellucida binding competence. It also describes reported roles in enabling surface relocation of proteins needed for oocyte zona interaction during capacitation (June 2022; Int J Mol Sci; URL https://doi.org/10.3390/ijms23126497) (grassi2022targetedanalysisof pages 1-2).

3.3.2. Hyaluronic acid (HA) binding–based sperm selection (2023 primary evidence with statistics)

Gómez-Torres et al. (Reproductive Sciences; July 2023; URL https://doi.org/10.1007/s43032-022-01031-9) quantified HSPA2 immunofluorescence positivity in human sperm (16 normozoospermic samples; ~300 cells/sample/condition; total ~19,200 cells assessed) and linked HSPA2 detection to HA-binding sperm selection:

• HSPA2-positive sperm fractions were 28.6% in uncapacitated sperm (US) and 22.9% in capacitated sperm (CS), with no significant difference (gomeztorres2023molecularchaperonehspa2 pages 4-6).
• HA-bound sperm showed substantially higher HSPA2 positivity (68.9%), significantly higher than US/CS (p<0.001) (gomeztorres2023molecularchaperonehspa2 pages 4-6).
• HA-unbound sperm showed 29.2% positivity (not different from US/CS; significantly lower than HA-bound, p<0.001) (gomeztorres2023molecularchaperonehspa2 pages 4-6).

The study further quantified subcellular staining patterns and showed shifts in localization patterns after HA selection, with one pattern (P3) becoming dominant among HA-bound sperm (46.6%) and another (P2) increasing (13.9%; p<0.001 vs US) (gomeztorres2023molecularchaperonehspa2 pages 4-6). The fraction of sperm bound in the HA assay was 21.4 ± 7.4% (gomeztorres2023molecularchaperonehspa2 pages 4-6).

Interpretation for functional annotation: these data support associating HSPA2 with sperm selection criteria linked to functional maturity (HA-binding competence) and with head-region localization patterns potentially relevant to gamete recognition/fertilization processes (gomeztorres2023molecularchaperonehspa2 pages 4-6).

3.4. Regulation and proteostasis coupling under stress

Sojka et al. (2023) observed that proteasome inhibition in cancer cell lines reduced cellular HSPA2 protein in a dose-dependent manner without a parallel decrease in HSPA2 mRNA, arguing for post-transcriptional mechanisms, and that the observed intracellular “loss” of HSPA2 was linked to increased extracellular release in EVs (sojka2023heatshockprotein pages 2-3). Autophagy/lysosome inhibition did not restore intracellular HSPA2 under those conditions (sojka2023heatshockprotein pages 2-3).

Recent developments and latest research (prioritizing 2023–2024)

4.1. 2023: HSPA2 as an extracellular vesicle-associated protein

The discovery/validation of HSPA2 in EV cargo using paralog-specific reagents and genetic controls (HSPA2 knockout) provides a mechanistic basis for studying HSPA2 in biofluids (e.g., urine EVs) and in tumor microenvironment communication (March 2023; URL https://doi.org/10.1038/s41598-023-31962-5) (sojka2023heatshockprotein pages 3-5, sojka2023heatshockprotein pages 9-10).

4.2. 2023: Functional stratification of HSPA2-positive sperm by HA selection

The quantitative enrichment of HSPA2-positive cells in HA-bound sperm provides updated evidence connecting HSPA2 detectability/localization with a sperm selection technique used in assisted reproduction settings (July 2023; URL https://doi.org/10.1007/s43032-022-01031-9) (gomeztorres2023molecularchaperonehspa2 pages 4-6).

4.3. 2024: Seminal plasma HSPA2 as a non-invasive biomarker of spermatogenic potential in azoospermia

Fietz et al. (Frontiers in Endocrinology; April 2024; URL https://doi.org/10.3389/fendo.2024.1327800) profiled seminal plasma proteomes from healthy controls and azoospermic subgroups and identified HSPA2 as a promising biomarker linked to spermatogenic function:

• Study cohorts: healthy controls (HC, n=8), obstructive azoospermia (OA, n=7), non-obstructive azoospermia (NOA) with mixed testicular atrophy (MTA, n=8), and NOA with Sertoli cell-only phenotype (SCO, n≈7–8 depending on analysis) (fietz2024proteomicbiomarkersin pages 1-2, fietz2024proteomicbiomarkersin pages 3-5).
• Across 917 quantified proteins, differential abundance criteria were p≤0.05 and fold-change ≥1.5 (fietz2024proteomicbiomarkersin pages 3-5).
• HSPA2 (UniProt P54652) was more abundant in HC than SCO with fold-change HC/SCO = 7.31 and adjusted p=0.0217 (fietz2024proteomicbiomarkersin pages 3-5).

This quantitative result is also visible in the paper’s Table 1 (image evidence) (fietz2024proteomicbiomarkersin media ce6a8253).

4.4. 2024: Circulating HSPA2 and diabetic myocardium — incident heart failure biomarker hypothesis

Conning-Rowland et al. (Cardiovascular Research; August 2024; URL https://doi.org/10.1093/cvr/cvae181) analyzed GTEx RNA-seq myocardial tissue to define diabetes-associated DEGs and validated certain targets at the plasma protein level in UK Biobank proteomics:

• GTEx analysis sample sizes after exclusions: 425 right atrial (RA) and 428 left ventricular (LV) samples (conningrowland2024thediabeticmyocardial pages 1-3).
• Diabetes was characterized by higher Hspa2 expression in LV myocardium and directionally concordant higher circulating HSPA2 protein (conningrowland2024thediabeticmyocardial pages 1-3).
• Higher circulating HSPA2 (highest quartile vs other quartiles) was associated with impaired LV contractility, higher LV mass, and increased incident heart failure and cardiovascular death (conningrowland2024thediabeticmyocardial pages 1-3).

The excerpt available here does not provide hazard ratios or p-values for these associations, so the strongest claim supported by the evidence retrieved is the directionality and existence of reported associations, not their effect sizes (conningrowland2024thediabeticmyocardial pages 1-3).

Current applications and real-world implementations

5.1. Male infertility diagnostics and decision support for sperm retrieval

A key near-term application is HSPA2 as a seminal plasma biomarker for non-invasive stratification of non-obstructive azoospermia and prediction of testicular sperm retrieval success. Fietz et al. (April 2024) specifically motivated their study by the clinical burden of NOA retrieval rates (~50%) and investigated HSPA2 as a candidate marker of spermatogenic function (fietz2024proteomicbiomarkersin pages 1-2). Their proteomics and validation strategy supports using HSPA2 measurement alongside other testis/germ-cell proteins to inform whether spermatogenesis is preserved (fietz2024proteomicbiomarkersin pages 1-2, fietz2024proteomicbiomarkersin pages 3-5).

5.2. Assisted reproduction and sperm selection methods

The HA-binding selection approach (often used to enrich sperm with features linked to maturity) is proposed as a context where HSPA2 immunodetection might complement classic semen analysis. The 2023 study’s observation that HA-bound sperm are enriched for HSPA2 positivity supports the practical notion that HSPA2 may be aligned with selection strategies aimed at improving fertilization-relevant sperm properties (gomeztorres2023molecularchaperonehspa2 pages 4-6).

5.3. Oncology: extracellular/EV HSP70-family biomarker concepts

A 2024 review on extracellular HSP70 in cancer describes extracellular HSP70 forms (membrane-associated, soluble, EV-associated) as potential tumor biomarkers and therapeutic targets, and notes HSPA2 among the HSP70-family members detected at the plasma membrane. While this does not establish HSPA2-specific clinical utility on its own, it positions HSPA2 within the extracellular-HSP70 biomarker/targeting framework in tumors (April 2024; URL https://doi.org/10.3389/fonc.2024.1388999) (sojka2023heatshockprotein pages 9-10).

5.4. Cardio-metabolic disease biomarker discovery

The 2024 Cardiovascular Research study suggests circulating HSPA2 may serve as a biomarker of LV remodeling/dysfunction and risk in diabetes, though quantitative performance metrics (e.g., HRs, AUC) are not available in the retrieved excerpt (conningrowland2024thediabeticmyocardial pages 1-3).

Expert synthesis and analysis (authoritative interpretations)

6.1. Proteostasis-centered view of HSPA2 function

Across recent primary studies, the most defensible “primary function” annotation is that HSPA2 is an ATP-dependent molecular chaperone supporting proteostasis (folding/refolding and quality control). The EV study’s mechanistic framing explicitly places HSPA2 in the broader proteostasis control machinery and emphasizes that its abundance and localization can be reshaped by proteotoxic stress, including redistribution into extracellular vesicles (sojka2023heatshockprotein pages 1-2, sojka2023heatshockprotein pages 2-3).

6.2. Reproductive specialization and measurable phenotypes

In reproduction-focused contexts, HSPA2 is repeatedly treated as a germ-cell enriched chaperone connected to meiosis and sperm surface remodeling, and recent quantitative work ties HSPA2 immunodetection to HA-binding sperm subpopulations. Importantly, HA binding stratifies HSPA2 positivity more strongly than capacitation alone in that dataset, which may imply that HSPA2 exposure/epitope accessibility or localization reflects sperm maturity states enriched by HA selection (gomeztorres2023molecularchaperonehspa2 pages 4-6).

6.3. Extracellular HSPA2 and biomarker feasibility

The EV-localization evidence provides a plausible biological route for HSPA2 detection in biofluids (e.g., urinary EVs, seminal plasma), consistent with the 2024 seminal plasma study demonstrating large differences (HC/SCO fold change 7.31) in HSPA2 abundance in a clinically relevant setting (fietz2024proteomicbiomarkersin pages 3-5, fietz2024proteomicbiomarkersin media ce6a8253). This convergence supports ongoing development of HSPA2 as a biomarker, while also emphasizing that extracellular detection may represent EV-associated protein rather than only soluble protein (sojka2023heatshockprotein pages 3-5, fietz2024proteomicbiomarkersin pages 3-5).

Key statistics and data points from recent studies (2023–2024)

• EV association under proteotoxic stress: bortezomib (32 nM) increased extracellular HSPA2 and nearly doubled EV number; EV mean size ~105.6 ± 0.6 nm (mode ~92.0 ± 5.7 nm) (Sojka et al., 2023; https://doi.org/10.1038/s41598-023-31962-5) (sojka2023heatshockprotein pages 3-5).

• HA selection in human sperm (n=16 donors; ~19,200 sperm scored): HSPA2-positive sperm 68.9% in HA-bound vs 28.6% uncapacitated and 22.9% capacitated; HA-bound sperm fraction 21.4 ± 7.4% (Gómez-Torres et al., 2023; https://doi.org/10.1007/s43032-022-01031-9) (gomeztorres2023molecularchaperonehspa2 pages 4-6).

• Seminal plasma proteomics (Frontiers in Endocrinology, April 2024; https://doi.org/10.3389/fendo.2024.1327800): 917 proteins quantified; HSPA2 HC/SCO fold-change 7.31 with adjusted p=0.0217 (Fietz et al., 2024), visible in Table 1 (fietz2024proteomicbiomarkersin pages 3-5, fietz2024proteomicbiomarkersin media ce6a8253).

• Diabetic myocardium transcriptomics (Cardiovascular Research, August 2024; https://doi.org/10.1093/cvr/cvae181): GTEx analysis included 425 RA and 428 LV samples; diabetes associated with higher Hspa2 expression in LV and directionally concordant higher circulating HSPA2, and highest-quartile circulating HSPA2 associated with LV dysfunction and increased incident heart failure/cardiovascular death (conningrowland2024thediabeticmyocardial pages 1-3).

Limitations of the current evidence set

• Direct enzymology (e.g., measured ATPase rates or client-specific substrate specificity) for human HSPA2 was not captured in the retrieved 2023–2024 excerpts; the ATPase/NBD function is supported via established HSP70 domain/function description in the HSPA2 EV study rather than HSPA2-specific kinetics (sojka2023heatshockprotein pages 1-2).

• Several disease/cancer claims are currently best supported at the “HSP70-family/extracellular HSP70” level or at the “HSPA2 is present/trafficked extracellularly” level, rather than as causal HSPA2-specific therapeutic targets with clinical efficacy data, because the most quantitative retrieved cancer-focused HSPA2 data are limited in this evidence set (sojka2023heatshockprotein pages 9-10, sojka2023heatshockprotein pages 3-5).

References (publication dates and URLs)

• Sojka DR et al. “Heat shock protein A2 is a novel extracellular vesicle-associated protein.” Scientific Reports. March 2023. https://doi.org/10.1038/s41598-023-31962-5 (sojka2023heatshockprotein pages 1-2, sojka2023heatshockprotein pages 9-10, sojka2023heatshockprotein pages 2-3, sojka2023heatshockprotein pages 3-5)

• Gómez-Torres MJ et al. “Molecular Chaperone HSPA2 Distribution During Hyaluronic Acid Selection in Human Sperm.” Reproductive Sciences. July 2023. https://doi.org/10.1007/s43032-022-01031-9 (gomeztorres2023molecularchaperonehspa2 pages 4-6)

• Fietz D et al. “Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men.” Frontiers in Endocrinology. April 2024. https://doi.org/10.3389/fendo.2024.1327800 (fietz2024proteomicbiomarkersin pages 1-2, fietz2024proteomicbiomarkersin pages 3-5, fietz2024proteomicbiomarkersin media ce6a8253)

• Conning-Rowland MS et al. “The diabetic myocardial transcriptome reveals Erbb3 and Hspa2 as a novel biomarkers of incident heart failure.” Cardiovascular Research. August 2024. https://doi.org/10.1093/cvr/cvae181 (conningrowland2024thediabeticmyocardial pages 1-3)

• Shriya S et al. “Bioinformatics analysis and alternative polyadenylation in Heat Shock Proteins 70 (HSP70) family members.” Int J Physiol Pathophysiol Pharmacol. January 2024. https://doi.org/10.62347/cwpe7813 (shriya2024bioinformaticsanalysisand pages 4-6)

• Grassi S et al. “Targeted Analysis of HSP70 Isoforms in Human Spermatozoa in the Context of Capacitation and Motility.” Int J Mol Sci. June 2022. https://doi.org/10.3390/ijms23126497 (grassi2022targetedanalysisof pages 1-2)

• Hu B et al. “Diversity of extracellular HSP70 in cancer: advancing from a molecular biomarker to a novel therapeutic target.” Frontiers in Oncology. April 2024. https://doi.org/10.3389/fonc.2024.1388999 (sojka2023heatshockprotein pages 9-10)

References

(sojka2023heatshockprotein pages 1-2): Damian Robert Sojka, Agata Abramowicz, Małgorzata Adamiec-Organiściok, Elżbieta Karnas, Łukasz Mielańczyk, Daria Kania, Sławomir Blamek, Ewa Telka, and Dorota Scieglinska. Heat shock protein a2 is a novel extracellular vesicle-associated protein. Scientific Reports, Mar 2023. URL: https://doi.org/10.1038/s41598-023-31962-5, doi:10.1038/s41598-023-31962-5. This article has 34 citations and is from a peer-reviewed journal.
(grassi2022targetedanalysisof pages 1-2): Sarah Grassi, Marie Bisconti, Baptiste Martinet, Vanessa Arcolia, Jean-François Simon, Ruddy Wattiez, Baptiste Leroy, and Elise Hennebert. Targeted analysis of hsp70 isoforms in human spermatozoa in the context of capacitation and motility. International Journal of Molecular Sciences, 23:6497, Jun 2022. URL: https://doi.org/10.3390/ijms23126497, doi:10.3390/ijms23126497. This article has 8 citations.
(sojka2023heatshockprotein pages 9-10): Damian Robert Sojka, Agata Abramowicz, Małgorzata Adamiec-Organiściok, Elżbieta Karnas, Łukasz Mielańczyk, Daria Kania, Sławomir Blamek, Ewa Telka, and Dorota Scieglinska. Heat shock protein a2 is a novel extracellular vesicle-associated protein. Scientific Reports, Mar 2023. URL: https://doi.org/10.1038/s41598-023-31962-5, doi:10.1038/s41598-023-31962-5. This article has 34 citations and is from a peer-reviewed journal.
(shriya2024bioinformaticsanalysisand pages 4-6): Srishti Shriya, Ramakrushna Paul, Neha Singh, Farhat Afza, and B. P. Jain. Bioinformatics analysis and alternative polyadenylation in heat shock proteins 70 (hsp70) family members. International journal of physiology, pathophysiology and pharmacology, 16 6:138-151, Jan 2024. URL: https://doi.org/10.62347/cwpe7813, doi:10.62347/cwpe7813. This article has 3 citations and is from a peer-reviewed journal.
(sojka2023heatshockprotein pages 2-3): Damian Robert Sojka, Agata Abramowicz, Małgorzata Adamiec-Organiściok, Elżbieta Karnas, Łukasz Mielańczyk, Daria Kania, Sławomir Blamek, Ewa Telka, and Dorota Scieglinska. Heat shock protein a2 is a novel extracellular vesicle-associated protein. Scientific Reports, Mar 2023. URL: https://doi.org/10.1038/s41598-023-31962-5, doi:10.1038/s41598-023-31962-5. This article has 34 citations and is from a peer-reviewed journal.
(sojka2023heatshockprotein pages 3-5): Damian Robert Sojka, Agata Abramowicz, Małgorzata Adamiec-Organiściok, Elżbieta Karnas, Łukasz Mielańczyk, Daria Kania, Sławomir Blamek, Ewa Telka, and Dorota Scieglinska. Heat shock protein a2 is a novel extracellular vesicle-associated protein. Scientific Reports, Mar 2023. URL: https://doi.org/10.1038/s41598-023-31962-5, doi:10.1038/s41598-023-31962-5. This article has 34 citations and is from a peer-reviewed journal.
(gomeztorres2023molecularchaperonehspa2 pages 4-6): María José Gómez-Torres, Natalia Huerta-Retamal, Paula Sáez-Espinosa, Laura Robles-Gómez, Manuel Avilés, and Jon Aizpurua. Molecular chaperone hspa2 distribution during hyaluronic acid selection in human sperm. Reproductive Sciences, 30:1176-1185, Jul 2023. URL: https://doi.org/10.1007/s43032-022-01031-9, doi:10.1007/s43032-022-01031-9. This article has 8 citations and is from a peer-reviewed journal.
(fietz2024proteomicbiomarkersin pages 1-2): Daniela Fietz, Raouda Sgaier, Liza O’Donnell, Peter G. Stanton, Laura F. Dagley, Andrew I. Webb, Hans-Christian Schuppe, Thorsten Diemer, and Adrian Pilatz. Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men. Frontiers in Endocrinology, Apr 2024. URL: https://doi.org/10.3389/fendo.2024.1327800, doi:10.3389/fendo.2024.1327800. This article has 13 citations.
(fietz2024proteomicbiomarkersin pages 3-5): Daniela Fietz, Raouda Sgaier, Liza O’Donnell, Peter G. Stanton, Laura F. Dagley, Andrew I. Webb, Hans-Christian Schuppe, Thorsten Diemer, and Adrian Pilatz. Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men. Frontiers in Endocrinology, Apr 2024. URL: https://doi.org/10.3389/fendo.2024.1327800, doi:10.3389/fendo.2024.1327800. This article has 13 citations.
(fietz2024proteomicbiomarkersin media ce6a8253): Daniela Fietz, Raouda Sgaier, Liza O’Donnell, Peter G. Stanton, Laura F. Dagley, Andrew I. Webb, Hans-Christian Schuppe, Thorsten Diemer, and Adrian Pilatz. Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men. Frontiers in Endocrinology, Apr 2024. URL: https://doi.org/10.3389/fendo.2024.1327800, doi:10.3389/fendo.2024.1327800. This article has 13 citations.
(conningrowland2024thediabeticmyocardial pages 1-3): Marcella S Conning-Rowland, Marilena Giannoudi, Michael Drozd, Oliver I Brown, Nadira Y Yuldasheva, Chew W Cheng, Paul J Meakin, Sam Straw, John Gierula, Ramzi A Ajjan, Mark T Kearney, Eylem Levelt, Lee D Roberts, Kathryn J Griffin, and Richard M Cubbon. The diabetic myocardial transcriptome reveals erbb3 and hspa2 as a novel biomarkers of incident heart failure. Cardiovascular Research, 120:1898-1906, Aug 2024. URL: https://doi.org/10.1093/cvr/cvae181, doi:10.1093/cvr/cvae181. This article has 10 citations and is from a domain leading peer-reviewed journal.

Citations

sojka2023heatshockprotein pages 1-2
grassi2022targetedanalysisof pages 1-2
sojka2023heatshockprotein pages 9-10
shriya2024bioinformaticsanalysisand pages 4-6
sojka2023heatshockprotein pages 3-5
sojka2023heatshockprotein pages 2-3
fietz2024proteomicbiomarkersin pages 3-5
conningrowland2024thediabeticmyocardial pages 1-3
fietz2024proteomicbiomarkersin pages 1-2
https://doi.org/10.1038/s41598-023-31962-5
https://doi.org/10.3389/fonc.2024.1388999
https://doi.org/10.3390/ijms23126497
https://doi.org/10.1007/s43032-022-01031-9
https://doi.org/10.3389/fendo.2024.1327800
https://doi.org/10.1093/cvr/cvae181
https://doi.org/10.62347/cwpe7813
https://doi.org/10.1038/s41598-023-31962-5,
https://doi.org/10.3390/ijms23126497,
https://doi.org/10.62347/cwpe7813,
https://doi.org/10.1007/s43032-022-01031-9,
https://doi.org/10.3389/fendo.2024.1327800,
https://doi.org/10.1093/cvr/cvae181,

📄 View Raw YAML

id: P54652
gene_symbol: HSPA2
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  HSPA2 (Heat shock-related 70 kDa protein 2, also known as Hsp70-2) is a
  member of the HSP70/HSPA molecular chaperone family. It functions as an
  ATP-dependent foldase chaperone, assisting in the folding and refolding of
  proteins through cycles of ATP binding, hydrolysis, and ADP release mediated
  by co-chaperones including DNAJ family members, STIP1, HSPBP1, and HSP110-
  type NEFs (DOI:10.62347/cwpe7813). HSPA2 is constitutively expressed in most
  tissues, with especially high levels in testis and skeletal muscle
  (PMID:7829106). It plays a pivotal role in spermatogenesis and male meiosis,
  where it associates with synaptonemal complexes in the nucleus of meiotic
  spermatocytes and is required for meiotic progression (PMID:8622925). HSPA2
  also supports sperm functional maturation, including cytoplasmic extrusion
  and plasma membrane remodeling required for zona pellucida binding competence
  (DOI:10.3390/ijms23126497). Quantitative immunofluorescence shows that
  hyaluronic acid (HA)-bound mature sperm are significantly enriched for HSPA2
  positivity (68.9% vs 28.6% in uncapacitated sperm; DOI:10.1007/s43032-022-01031-9).
  Recent work demonstrates that HSPA2 is an extracellular vesicle (EV)-associated
  protein; proteotoxic stress (proteasome inhibition) shifts HSPA2 from
  intracellular pools to extracellular release in EVs, validated using CRISPR/
  Cas9 HSPA2 knockout controls (DOI:10.1038/s41598-023-31962-5). Seminal plasma
  proteomics identifies HSPA2 as a biomarker of spermatogenic function, with
  7.3-fold higher abundance in healthy controls vs Sertoli cell-only azoospermia
  (DOI:10.3389/fendo.2024.1327800). In cardio-metabolic contexts, circulating
  HSPA2 is elevated in diabetic myocardium and associated with increased incident
  heart failure and LV dysfunction (DOI:10.1093/cvr/cvae181). HSPA2 has a
  nucleotide-binding domain (NBD/ATPase domain) and a substrate-binding domain
  (SBD), which are allosterically coupled such that ATP hydrolysis increases
  affinity for client proteins. Its interaction network includes SHCBP1L, which
  supports spindle integrity during male meiosis (DOI:10.62347/cwpe7813).
existing_annotations:
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 to nucleus based on phylogenetic inference from
      multiple HSP70 orthologs across species. HSP70 family members are well
      documented to localize to the nucleus, particularly under stress conditions
      and during specific cell cycle stages. For HSPA2 specifically, the mouse
      ortholog (Hsp70-2/P17156) has been shown to associate with synaptonemal
      complexes in the nucleus of meiotic spermatocytes (PMID:8622925). HSPA2
      was also detected in the human sperm nucleus by proteomics (PMID:21630459).
      The IBA annotation is well supported by phylogenetic evidence and
      consistent with known biology.
    action: ACCEPT
    reason: >-
      HSP70 family members are known to localize to the nucleus. HSPA2 in
      particular is associated with synaptonemal complexes within the nucleus
      of meiotic spermatocytes (PMID:8622925), and was detected in the sperm
      nucleus proteome (PMID:21630459). The IBA annotation from phylogenetic
      inference is well supported.
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          We previously found that HSP70-2 is associated with synaptonemal
          complexes in the nucleus of meiotic spermatocytes from mice and
          hamsters.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 to cytoplasm based on phylogenetic inference. HSP70
      family members are predominantly cytoplasmic proteins. UniProt notes the
      subcellular location of HSPA2 as cytoplasm/cytoskeleton/spindle
      (UniProt P54652). Hageman et al. (PMID:21231916) expressed HSPA2 in cell
      culture and demonstrated cytoplasmic chaperone activities (luciferase
      refolding, polyQ aggregation suppression), confirming cytoplasmic
      localization. This is a well-supported core localization.
    action: ACCEPT
    reason: >-
      HSPA2 is a cytoplasmic chaperone as demonstrated by functional assays
      in the cytoplasm (PMID:21231916) and consistent with the known biology
      of HSP70 family members. The IBA phylogenetic annotation is correct.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase and on the suppression of
          aggregation of a non-foldable polyQ (polyglutamine)-expanded
          Huntingtin fragment
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 to plasma membrane based on phylogenetic inference.
      Several HSP70 family members have been shown to localize to the plasma
      membrane and cell surface, particularly under stress conditions. For HSPA2,
      the mouse ortholog (P17156) has been annotated to cell surface
      (GO_REF:0000107, Ensembl Compara). UniProt notes that HSPA2 is a component
      of the CatSper complex (by similarity), which is a sperm cell surface ion
      channel complex. The IBA annotation is plausible but plasma membrane
      localization is not a core feature of HSPA2 function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Plasma membrane localization of HSP70 family members is documented but
      is not the primary site of HSPA2 function. The main functional
      localizations are cytoplasm/cytosol and nucleus (synaptonemal complex).
      Plasma membrane association may relate to its role in the CatSper complex
      in sperm or stress-related surface presentation.
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 for ATP hydrolysis activity based on phylogenetic
      inference from HSP70 orthologs. ATP hydrolysis is the fundamental
      mechanistic step driving the HSP70 chaperone cycle. The N-terminal
      nucleotide-binding domain of HSPA2 (residues 2-389) binds and hydrolyzes
      ATP, and the crystal structure of the HSPA2 ATPase domain has been solved
      in complex with ADP and phosphate (PDB:3I33, PMID:20072699). UniProt
      describes the allosteric coupling between ATP hydrolysis and substrate
      binding (UniProt P54652). This is a core molecular function of HSPA2.
    action: ACCEPT
    reason: >-
      ATP hydrolysis is the fundamental catalytic activity of all HSP70 family
      members, driving the chaperone cycle. The HSPA2 ATPase domain crystal
      structure confirms this activity (PDB:3I33). The IBA annotation is
      strongly supported.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          HSPA6 has a functional substrate-binding domain and possesses
          intrinsic ATPase activity that is as high as that of the canonical
          HSPA1A when stimulated by J-proteins
- term:
    id: GO:0031072
    label: heat shock protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 for heat shock protein binding based on
      phylogenetic inference. HSP70 family members interact extensively with
      co-chaperones including HSP40/DNAJ proteins, HSPBP1, and BAG domain
      proteins. HSPA2 has been shown by IPI evidence to interact with HSPBP1
      (Q9NZL4) in multiple studies (PMID:16189514, PMID:16713569, PMID:25416956,
      PMID:28514442, PMID:33961781, PMID:35271311, PMID:40205054). HSPA2 also
      interacts with BAG4 (O95429) and DNAJA3 (UniProt P54652). These
      interactions with co-chaperones are integral to the HSP70 chaperone cycle.
    action: ACCEPT
    reason: >-
      HSP70 chaperones fundamentally depend on interactions with co-chaperones
      (HSP40/DNAJ, NEFs like HSPBP1 and BAG proteins) for their function.
      The extensive IPI evidence for HSPA2-HSPBP1 interaction across multiple
      studies validates this annotation. This is a core molecular function.
- term:
    id: GO:0044183
    label: protein folding chaperone
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 as a protein folding chaperone based on
      phylogenetic inference from HSP70 orthologs including DnaK. This is the
      central molecular function of HSPA2. Hageman et al. (PMID:21231916)
      directly demonstrated that HSPA2 has chaperone activity by showing it
      supports refolding of heat-denatured luciferase and suppresses
      aggregation of polyQ-expanded Huntingtin. UniProt describes HSPA2 as a
      "molecular chaperone implicated in a wide variety of cellular processes,
      including protection of the proteome from stress, folding and transport
      of newly synthesized polypeptides" (UniProt P54652). This is the core
      molecular function annotation for HSPA2.
    action: ACCEPT
    reason: >-
      Protein folding chaperone activity is the core molecular function of
      HSPA2, directly demonstrated by in vitro assays (PMID:21231916) and
      consistent with the well-characterized HSP70 chaperone mechanism. The
      IBA annotation is strongly supported by both phylogenetic and
      experimental evidence.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase and on the suppression of
          aggregation of a non-foldable polyQ (polyglutamine)-expanded
          Huntingtin fragment
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 to cytosol based on phylogenetic inference.
      HSPA2 is a cytosolic chaperone. This annotation is also supported by
      direct experimental evidence (IDA) from PMID:21231916, where HSPA2 was
      overexpressed and shown to function in the cytosol. The IBA annotation
      is consistent with the IDA evidence and with the known biology of
      HSP70 family members.
    action: ACCEPT
    reason: >-
      Cytosol is the primary functional compartment for HSPA2 chaperone
      activity, supported by both phylogenetic inference and direct experimental
      evidence (PMID:21231916 IDA). The IBA annotation is correct.
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation of HSPA2 for involvement in protein refolding based on
      phylogenetic inference from HSP70 orthologs. Protein refolding is a core
      biological process mediated by HSP70 chaperones. Hageman et al.
      (PMID:21231916) directly demonstrated HSPA2 supports refolding of
      heat-denatured luciferase, providing experimental confirmation. This
      IBA annotation is strongly supported.
    action: ACCEPT
    reason: >-
      Protein refolding is a core function of HSP70 chaperones, directly
      demonstrated for HSPA2 by luciferase refolding assays (PMID:21231916).
      The IBA annotation is well supported by phylogenetic and experimental
      evidence.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase
- term:
    id: GO:0000166
    label: nucleotide binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation of HSPA2 for nucleotide binding based on UniProtKB/Swiss-Prot
      keyword mapping (KW-0547 Nucleotide-binding). HSPA2 has a well-characterized
      nucleotide-binding domain (residues 2-389) with multiple ATP binding sites
      confirmed by crystal structure (PDB:3I33). This is a correct but overly
      general annotation; GO:0005524 "ATP binding" is more specific and already
      annotated. Nonetheless, nucleotide binding is technically correct as a
      parent term.
    action: ACCEPT
    reason: >-
      Nucleotide binding is correct for HSPA2, which has an N-terminal
      nucleotide-binding domain confirmed by crystal structure. While broader
      than the more specific ATP binding annotation (GO:0005524), it is not
      incorrect as an IEA annotation derived from keyword mapping.
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IEA annotation of HSPA2 for ATP binding based on combined automated
      annotation using InterPro (IPR013126 HSP70 family) and UniProtKB keyword
      (KW-0067 ATP-binding). The crystal structure of HSPA2 NBD in complex with
      ADP and phosphate (PDB:3I33, PMID:20072699) directly confirms ATP binding.
      UniProt annotates multiple ATP binding sites at residues 13-16, 72,
      205-207, 271-278, and 342-345 (UniProt P54652). This is a well-supported
      core molecular function.
    action: ACCEPT
    reason: >-
      ATP binding is fundamental to HSPA2 function and is confirmed by
      crystal structure (PDB:3I33) and multiple annotated binding sites in
      the NBD domain. The IEA annotation is correct.
- term:
    id: GO:0005819
    label: spindle
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      IEA annotation of HSPA2 to spindle based on UniProtKB/Swiss-Prot
      subcellular location vocabulary mapping. UniProt records HSPA2 subcellular
      location as "Cytoplasm, cytoskeleton, spindle" based on similarity to
      mouse Hsp70-2 (P17156). The mouse ortholog co-localizes with SHCBP1L
      at the spindle during meiosis. This is consistent with the meiotic
      spindle localization annotated elsewhere (GO:0072687). The more specific
      term GO:0072687 "meiotic spindle" is preferable, but spindle is not
      wrong as a broader term.
    action: ACCEPT
    reason: >-
      HSPA2 localizes to the meiotic spindle based on similarity data from
      the mouse ortholog (UniProt P17156). The broader term "spindle" is
      acceptable as an IEA annotation, though GO:0072687 "meiotic spindle"
      is more specific and also annotated.
- term:
    id: GO:0006986
    label: response to unfolded protein
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      IEA annotation of HSPA2 for response to unfolded protein based on ARBA
      machine learning. As a member of the HSP70 chaperone family, HSPA2 is
      involved in the cellular response to unfolded proteins. UniProt describes
      HSPA2 as a molecular chaperone involved in "protection of the proteome
      from stress" and "the re-folding of misfolded proteins" (UniProt P54652).
      HSPA2 is constitutively expressed but its role in proteostasis is
      consistent with involvement in unfolded protein response.
    action: ACCEPT
    reason: >-
      HSPA2 is a molecular chaperone that assists in refolding of misfolded
      proteins and suppresses protein aggregation (PMID:21231916), which are
      key components of the response to unfolded protein. The IEA annotation
      is correct.
- term:
    id: GO:0007283
    label: spermatogenesis
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IEA annotation of HSPA2 for involvement in spermatogenesis based on
      combined automated annotation using orthology to mouse Hsp70-2 (P17156)
      and UniProtKB keyword (KW-0744 Spermatogenesis). The mouse knockout
      study (PMID:8622925) directly demonstrated that Hsp70-2 disruption causes
      failed meiosis, germ cell apoptosis, and male infertility. HSPA2 is
      the human ortholog and is constitutively expressed at very high levels
      in testis (PMID:7829106). This is a core specialized function of HSPA2.
    action: ACCEPT
    reason: >-
      Spermatogenesis is a core specialized function of HSPA2, demonstrated
      by mouse knockout studies showing male infertility (PMID:8622925) and
      supported by high testicular expression (PMID:7829106). The IEA
      annotation is strongly supported.
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not
          synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm,
          and were infertile.
      - reference_id: PMID:7829106
        supporting_text: >-
          HSPA2 is constitutively expressed in most tissues, with very high
          levels in testis and skeletal muscle.
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      IEA annotation of HSPA2 for ATP hydrolysis activity based on InterPro
      record (IPR013126 HSP70 family) to GO term mapping. This is a duplicate
      of the IBA annotation for the same term (GO:0016887). ATP hydrolysis is
      the core catalytic activity of the HSP70 ATPase domain. The crystal
      structure of the HSPA2 ATPase domain (PDB:3I33) confirms this activity.
      Duplicate annotations with different evidence codes are acceptable.
    action: ACCEPT
    reason: >-
      ATP hydrolysis activity is the core catalytic function of HSPA2,
      confirmed by crystal structure of the ATPase domain (PDB:3I33). The
      IEA from InterPro is correct and consistent with the IBA annotation.
- term:
    id: GO:0019899
    label: enzyme binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      IEA annotation of HSPA2 for enzyme binding based on ARBA machine learning.
      HSPA2 interacts with METTL21A (HSPA-KMT), an enzyme that trimethylates
      Lys-564 of HSPA2 (PMID:23921388). This qualifies as enzyme binding.
      However, this is a somewhat uninformative term; the interaction with
      METTL21A is more accurately described as HSPA2 being a substrate of this
      methyltransferase rather than HSPA2 having "enzyme binding" as a core
      molecular function. As a chaperone, HSPA2 also interacts with numerous
      enzymes as clients.
    action: KEEP_AS_NON_CORE
    reason: >-
      Enzyme binding is technically correct (HSPA2 interacts with METTL21A
      methyltransferase, PMID:23921388), but it is not an informative
      description of HSPA2 core function. As a chaperone, HSPA2 binds many
      proteins including enzymes as clients or regulatory partners.
- term:
    id: GO:0030154
    label: cell differentiation
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation of HSPA2 for cell differentiation based on UniProtKB
      keyword mapping (KW-0221 Differentiation). This is a very broad term.
      The differentiation keyword in UniProt for HSPA2 presumably relates to
      its role in spermatogenesis, specifically spermatid differentiation and
      development. The more specific terms GO:0007283 "spermatogenesis" and
      GO:0007286 "spermatid development" are already annotated and are more
      informative. Cell differentiation is too generic to be useful for HSPA2.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      GO:0030154 "cell differentiation" is too broad and uninformative for
      HSPA2. The relevant differentiation context is spermatogenesis/spermatid
      development, which is already captured by more specific annotations
      (GO:0007283, GO:0007286). This general term adds no useful information.
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      IEA annotation of HSPA2 for protein refolding based on ARBA machine
      learning. This is a duplicate of the IBA and IDA annotations for the
      same term. Protein refolding is a core function of HSPA2, directly
      demonstrated by luciferase refolding assays (PMID:21231916). The IEA
      annotation is correct and consistent with experimental evidence.
    action: ACCEPT
    reason: >-
      Protein refolding is a core function of HSPA2, confirmed by
      experimental evidence (PMID:21231916 IDA) and phylogenetic inference
      (IBA). The IEA annotation is correct.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      GO:0051082 "unfolded protein binding" is being obsoleted (go-ontology#30962)
      because the term describes binding rather than the actual molecular activity.
      HSPA2 is a bona fide ATP-dependent foldase chaperone, not merely a passive
      binder of unfolded proteins. The IEA annotation via ARBA machine learning
      correctly identifies the chaperone-related function but uses the wrong term.
      UniProt describes HSPA2 as a "molecular chaperone implicated in a wide variety
      of cellular processes, including protection of the proteome from stress,
      folding and transport of newly synthesized polypeptides" (UniProt P54652).
      The correct replacement is GO:0044183 "protein folding chaperone", which
      already has an IBA annotation for this gene, further confirming the
      appropriateness of the replacement.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted per go-ontology#30962 because it conflates
      passive binding with active chaperone function. For HSP70 family members
      like HSPA2, the correct term is GO:0044183 "protein folding chaperone"
      (foldase), as the protein actively assists protein folding through
      ATP-dependent cycles. This IEA annotation should be replaced with the
      correct MF term.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16189514
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interaction with
      HSPBP1 (Q9NZL4) detected in Rual et al. (PMID:16189514), a proteome-scale
      yeast two-hybrid study of human protein-protein interactions. HSPBP1 is a
      known HSP70 co-chaperone/nucleotide exchange factor. The interaction between
      HSPA2 and HSPBP1 is functionally relevant and has been confirmed in multiple
      independent studies. However, "protein binding" is uninformative; this
      interaction is better captured by GO:0031072 "heat shock protein binding"
      (already annotated via IBA) or by the co-chaperone interaction context.
    action: MODIFY
    reason: >-
      The interaction with HSPBP1 (a co-chaperone/NEF) is real and confirmed
      across multiple studies, but GO:0005515 "protein binding" is uninformative.
      This interaction is already captured by the more specific GO:0031072
      "heat shock protein binding" IBA annotation. Replace with the more
      specific term.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16713569
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interaction with
      HSPBP1 (Q9NZL4) detected in Lim et al. (PMID:16713569), a protein-protein
      interaction network study for inherited ataxias. This is another detection
      of the HSPA2-HSPBP1 co-chaperone interaction. As with the other HSPBP1
      interaction entries, "protein binding" is uninformative and the interaction
      is better represented by GO:0031072 "heat shock protein binding."
    action: MODIFY
    reason: >-
      Same rationale as the PMID:16189514 entry. HSPA2-HSPBP1 interaction is
      a co-chaperone interaction better described by GO:0031072 "heat shock
      protein binding" rather than the generic GO:0005515.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25036637
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interactions detected
      in Taipale et al. (PMID:25036637), a quantitative chaperone interaction
      network study. The GOA data shows interactions with BAG4 (O95429), HSF2
      (Q03933), and Q96BE0. BAG4 is a BAG domain co-chaperone that acts as a
      nucleotide exchange factor for HSP70s. HSF2 is a heat shock transcription
      factor. These are functionally relevant interactions for a chaperone.
      However, "protein binding" remains uninformative; these interactions
      reflect chaperone-co-chaperone interactions or client binding.
    action: MODIFY
    reason: >-
      The interactions with BAG4 (co-chaperone) and HSF2 are real and
      functionally relevant from a chaperone network study, but "protein
      binding" is uninformative. The BAG4 interaction is better described
      by GO:0031072 "heat shock protein binding."
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interactions with
      TRIM38 (O00635) and HSPBP1 (Q9NZL4) detected in Rolland et al.
      (PMID:25416956), a proteome-scale interactome mapping study. The HSPBP1
      interaction is a well-validated co-chaperone interaction. TRIM38 is an E3
      ubiquitin ligase; its interaction with HSPA2 could relate to chaperone-
      mediated targeting of substrates for ubiquitination. "Protein binding"
      is too generic for these functionally informative interactions.
    action: MODIFY
    reason: >-
      Contains validated co-chaperone interaction (HSPBP1) and ubiquitin ligase
      interaction (TRIM38). GO:0005515 "protein binding" is uninformative; the
      HSPBP1 interaction is better captured by GO:0031072 "heat shock protein
      binding."
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interaction with
      HSPBP1 (Q9NZL4) detected in Huttlin et al. (PMID:28514442), a study on
      the architecture of the human interactome. This is yet another independent
      confirmation of the HSPA2-HSPBP1 co-chaperone interaction. "Protein
      binding" is uninformative for this functionally well-characterized
      interaction.
    action: MODIFY
    reason: >-
      Another confirmation of HSPA2-HSPBP1 co-chaperone interaction. GO:0005515
      is uninformative; better captured by GO:0031072.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31515488
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interaction with
      TRIM38 (O00635) detected in Sahni et al. (PMID:31515488), a study on
      disruption of protein interactions by genetic variants. The HSPA2-TRIM38
      interaction may relate to chaperone-assisted ubiquitination. "Protein
      binding" is uninformative.
    action: MODIFY
    reason: >-
      The TRIM38 interaction may reflect chaperone-ubiquitin ligase cooperation,
      but GO:0005515 "protein binding" is uninformative. A more specific term
      would be appropriate, but without detailed characterization of the
      functional consequence, the best replacement is GO:0031072 for the
      general HSP70 interaction context.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interaction with
      BAG4 (O95429) detected in Luck et al. (PMID:32296183), a reference map
      of the human binary protein interactome. BAG4 is a co-chaperone containing
      a BAG domain that functions as a nucleotide exchange factor for HSP70
      proteins. This is a functionally relevant chaperone-co-chaperone
      interaction. "Protein binding" is uninformative.
    action: MODIFY
    reason: >-
      BAG4 is an HSP70 co-chaperone; this interaction is functionally relevant
      and better described by GO:0031072 "heat shock protein binding" rather
      than the generic GO:0005515.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32814053
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on a large number of
      interactions detected in Mair et al. (PMID:32814053), an interactome
      mapping study focused on neurodegenerative disease proteins. The GOA
      data lists interactions with many partners including HTT (P42858), SSB,
      SOCS6, multiple zinc finger proteins, and others. Some of these (HTT)
      are likely chaperone-client interactions relevant to aggregation
      suppression, consistent with the role of HSPA2 in suppressing polyQ
      aggregation (PMID:21231916). However, many interactions from large-scale
      screens may be non-specific or represent transient chaperone-client
      contacts. "Protein binding" is uninformative.
    action: MODIFY
    reason: >-
      Large-scale interactome study detecting many HSPA2 interactions. Some
      (HTT, DNAJA3) are functionally relevant for chaperone biology. However,
      GO:0005515 "protein binding" is uninformative. The chaperone-client and
      chaperone-co-chaperone interactions are better captured by existing
      annotations (GO:0044183, GO:0031072).
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interactions with
      HSF2 (Q03933) and HSPBP1 (Q9NZL4) detected in Huttlin et al.
      (PMID:33961781), a dual proteome-scale network study. Both are
      functionally relevant interactions: HSPBP1 is a co-chaperone and HSF2
      is a heat shock transcription factor that could be regulated by
      chaperone interactions. "Protein binding" is uninformative.
    action: MODIFY
    reason: >-
      Both interaction partners (HSPBP1 co-chaperone, HSF2 transcription factor)
      are functionally relevant. GO:0005515 is uninformative; these are better
      captured by GO:0031072.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35271311
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interaction with
      HSPBP1 (Q9NZL4) detected in Cho et al. (PMID:35271311), the OpenCell
      endogenous tagging study. This is another independent confirmation of the
      HSPA2-HSPBP1 co-chaperone interaction using endogenous tagging, a method
      less prone to overexpression artifacts. "Protein binding" is uninformative.
    action: MODIFY
    reason: >-
      Another independent confirmation of HSPA2-HSPBP1 interaction using
      endogenous tagging. GO:0005515 is uninformative; better captured by
      GO:0031072.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  review:
    summary: >-
      IPI annotation of HSPA2 for protein binding based on interactions with
      HSF2 (Q03933) and HSPBP1 (Q9NZL4) detected in Kim et al. (PMID:40205054),
      a multimodal cell mapping study. These are the same well-validated
      interaction partners seen across multiple studies. "Protein binding"
      is uninformative.
    action: MODIFY
    reason: >-
      Well-validated interactions with HSPBP1 and HSF2. GO:0005515 is
      uninformative; better captured by GO:0031072.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
- term:
    id: GO:0000795
    label: synaptonemal complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 to synaptonemal complex based on Ensembl Compara
      orthology transfer from mouse Hsp70-2 (P17156). The mouse knockout study
      (PMID:8622925) directly demonstrated that HSP70-2 is associated with
      synaptonemal complexes in meiotic spermatocytes: "We previously found
      that HSP70-2 is associated with synaptonemal complexes in the nucleus of
      meiotic spermatocytes from mice and hamsters. While synaptonemal complexes
      assembled in Hsp70-2 -/- spermatocytes, structural abnormalities became
      apparent in these cells by late prophase." This is a well-supported
      specialized localization for HSPA2 during male meiosis.
    action: ACCEPT
    reason: >-
      Synaptonemal complex localization is directly demonstrated for the mouse
      ortholog Hsp70-2 in meiotic spermatocytes (PMID:8622925) and is a key
      aspect of the specialized meiotic function of HSPA2. The IEA transfer
      from mouse is well justified.
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          We previously found that HSP70-2 is associated with synaptonemal
          complexes in the nucleus of meiotic spermatocytes from mice and
          hamsters. While synaptonemal complexes assembled in Hsp70-2 -/-
          spermatocytes, structural abnormalities became apparent in these
          cells by late prophase
- term:
    id: GO:0001673
    label: male germ cell nucleus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 to male germ cell nucleus based on Ensembl Compara
      orthology transfer from mouse Hsp70-2 (P17156). The mouse ortholog has been
      demonstrated to localize within the nucleus of meiotic spermatocytes where
      it associates with synaptonemal complexes (PMID:8622925). HSPA2 was also
      detected in the human sperm nucleus proteome (PMID:21630459). This is a
      well-supported specialized localization.
    action: ACCEPT
    reason: >-
      Male germ cell nucleus localization is strongly supported by the mouse
      knockout study showing association with synaptonemal complexes in
      spermatocyte nuclei (PMID:8622925) and by proteomics detection in human
      sperm nuclei (PMID:21630459).
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          HSP70-2 is associated with synaptonemal complexes in the nucleus of
          meiotic spermatocytes from mice and hamsters.
- term:
    id: GO:0009986
    label: cell surface
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 to cell surface based on Ensembl Compara orthology
      transfer from mouse Hsp70-2 (P17156). HSP70 family members have been
      reported at the cell surface in various contexts, particularly in sperm
      cells where HSPA2 may be surface-exposed as part of the CatSper complex
      or other surface structures. This is consistent with the CatSper complex
      annotation and the plasma membrane IBA annotation. However, cell surface
      localization is not a core feature of HSPA2 function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Cell surface localization is plausible for HSPA2, particularly in sperm
      cells, but is not a core functional localization. The primary functional
      compartments are cytosol and nucleus (synaptonemal complex).
- term:
    id: GO:0036128
    label: CatSper complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 as part of the CatSper complex based on Ensembl
      Compara orthology transfer from mouse Hsp70-2 (P17156). UniProt notes
      "Component of the CatSper complex" for HSPA2 (by similarity to mouse).
      CatSper is a sperm-specific calcium ion channel complex essential for
      sperm motility and male fertility. HSPA2 association with CatSper is
      consistent with its specialized role in spermatogenesis and sperm
      function.
    action: KEEP_AS_NON_CORE
    reason: >-
      CatSper complex membership is supported by mouse ortholog data and
      UniProt annotation (by similarity). This is a specialized sperm function
      consistent with the spermatogenesis role, but is a secondary localization
      rather than a core molecular function annotation.
- term:
    id: GO:0048156
    label: tau protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 for tau protein binding based on Ensembl Compara
      orthology transfer from rat Hspa2 (P14659). HSP70 family members,
      particularly HSPA8/Hsc70, have been shown to interact with tau and
      participate in its degradation through chaperone-mediated autophagy.
      However, this annotation is transferred from the rat ortholog and the
      tau binding evidence may be stronger for other HSP70 family members
      (particularly HSPA8). For HSPA2, tau binding would represent a general
      chaperone-client interaction rather than a specific function.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Tau protein binding is likely a general chaperone-client interaction
      shared across HSP70 family members rather than a specific function of
      HSPA2. The annotation is transferred from rat and may be more relevant
      to HSPA8/Hsc70 which is the primary constitutive HSP70 in neurons.
      For HSPA2, which has a specialized testis/meiosis role, tau binding
      is not a core function.
- term:
    id: GO:0051087
    label: protein-folding chaperone binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 for protein-folding chaperone binding based on
      Ensembl Compara orthology transfer from rat Hspa2 (P14659). HSP70 family
      members interact extensively with co-chaperones (DNAJ/HSP40, HSPBP1, BAG
      domain proteins, HOP/STIP1). HSPA2 has demonstrated interactions with
      HSPBP1 across multiple studies (PMID:16189514, PMID:16713569, PMID:25416956,
      PMID:28514442, PMID:33961781, PMID:35271311, PMID:40205054) and with BAG4
      (PMID:25036637, PMID:32296183) and DNAJA3 (PMID:32814053). This is a
      well-supported function. Note this describes HSPA2 binding to other
      chaperones (HSPA2 as the subject), which is essentially the reciprocal
      of heat shock protein binding.
    action: ACCEPT
    reason: >-
      HSPA2 binding to co-chaperones (HSPBP1, BAG4, DNAJA3) is extensively
      documented by IPI evidence across multiple studies. This is a core
      aspect of HSP70 function.
- term:
    id: GO:0051861
    label: glycolipid binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 for glycolipid binding based on Ensembl Compara
      orthology transfer from mouse Hsp70-2 (P17156). This annotation likely
      relates to the reported interaction of HSP70 family members with
      sulfogalactosylglycerolipid (SGG/seminolipid) on the sperm surface,
      which has been proposed to play a role in sperm-egg interaction. This is
      a specialized sperm biology function. However, glycolipid binding is
      not a well-established molecular function of HSPA2 based on direct
      evidence and may represent an over-annotation based on indirect or
      limited evidence.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Glycolipid binding is a specialized annotation transferred from the mouse
      ortholog that is based on limited evidence about HSP70-seminolipid
      interactions on sperm surfaces. This is not a well-characterized core
      molecular function of HSPA2 and likely represents over-annotation.
- term:
    id: GO:0072687
    label: meiotic spindle
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation of HSPA2 to meiotic spindle based on Ensembl Compara
      orthology transfer from mouse Hsp70-2 (P17156). UniProt notes that HSPA2
      co-localizes with SHCBP1L at the spindle during meiosis (by similarity).
      This is consistent with the specialized meiotic function of HSPA2 in male
      germ cells. The more specific meiotic spindle term is appropriate given
      HSPA2's established role in male meiosis (PMID:8622925).
    action: ACCEPT
    reason: >-
      Meiotic spindle localization is supported by mouse ortholog data showing
      HSPA2 co-localizes with SHCBP1L at the spindle during meiosis (UniProt,
      by similarity to P17156). This is consistent with HSPA2's essential role
      in male meiosis (PMID:8622925).
- term:
    id: GO:0007283
    label: spermatogenesis
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS annotation of HSPA2 for spermatogenesis based on manual transfer from
      mouse ortholog Hsp70-2 (P17156). The mouse knockout study (PMID:8622925)
      definitively demonstrated that Hsp70-2 is required for spermatogenesis:
      male knockout mice lacked postmeiotic spermatids and mature sperm and
      were infertile. HSPA2 is the human ortholog with 98.2% amino acid
      identity (PMID:7829106). This is a core specialized function.
    action: ACCEPT
    reason: >-
      Spermatogenesis is a core specialized function, directly demonstrated
      by mouse knockout (PMID:8622925). The ISS transfer from mouse is
      strongly justified by high sequence conservation (98.2% identity,
      PMID:7829106).
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not
          synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm,
          and were infertile.
- term:
    id: GO:0072687
    label: meiotic spindle
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS annotation of HSPA2 to meiotic spindle based on manual transfer from
      mouse ortholog Hsp70-2 (P17156). UniProt notes HSPA2 co-localizes with
      SHCBP1L at the spindle during meiosis (by similarity). This is a
      duplicate of the IEA annotation for the same term. Both are supported
      by the mouse ortholog data.
    action: ACCEPT
    reason: >-
      Meiotic spindle localization is well supported by mouse ortholog data
      (by similarity to P17156). The ISS annotation is correct and consistent
      with the IEA annotation.
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS annotation of HSPA2 for response to heat based on manual transfer from
      orthologs by AgBase. HSPA2 is a member of the HSP70 family, which are
      classically involved in the heat shock response. However, HSPA2 is
      notably constitutively expressed rather than heat-inducible. The original
      characterization (PMID:7829106) describes HSPA2 as constitutively
      expressed. UniProt keywords include "Stress response" but HSPA2 is not a
      canonical heat-inducible HSP70 (unlike HSPA1A/HSPA6). While HSPA2 likely
      participates in protein quality control during heat stress as a constitutive
      chaperone, "response to heat" may be somewhat misleading for a
      constitutively expressed member. This is a non-core annotation.
    action: KEEP_AS_NON_CORE
    reason: >-
      HSPA2 is constitutively expressed (PMID:7829106) rather than
      heat-inducible, distinguishing it from canonical heat-inducible HSP70s
      like HSPA1A. It may participate in heat stress response through its
      constitutive chaperone activity, but "response to heat" is not a core
      or distinguishing function of HSPA2.
    supported_by:
      - reference_id: PMID:7829106
        supporting_text: >-
          HSPA2 is constitutively expressed in most tissues, with very high
          levels in testis and skeletal muscle.
- term:
    id: GO:0009409
    label: response to cold
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS annotation of HSPA2 for response to cold based on manual transfer from
      orthologs by AgBase. HSP70 family members can be induced by various
      stresses including cold. However, HSPA2 is constitutively expressed
      (PMID:7829106) and there is limited direct evidence for its specific
      involvement in cold stress response in humans. This annotation likely
      derives from studies of HSP70 orthologs in other organisms (e.g., fish)
      where cold stress induces HSP70 expression. For HSPA2, this is at best a
      peripheral function.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      HSPA2 is constitutively expressed (PMID:7829106) and there is no strong
      evidence for specific involvement in cold stress response. This
      annotation likely derives from studies in distantly related organisms
      where HSP70 induction by cold is documented, but this is not a core or
      well-established function of human HSPA2.
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  review:
    summary: >-
      HDA annotation of HSPA2 to membrane based on high-throughput proteomics
      of NK cell membranes (PMID:19946888). HSPA2 was detected in the membrane
      proteome of NK cells. HSP70 family members are known to associate with
      membranes, particularly under stress conditions, and have been detected
      on cell surfaces. However, "membrane" is a very broad cellular component
      term and membrane association is not a core localization of HSPA2.
    action: KEEP_AS_NON_CORE
    reason: >-
      HSPA2 detection in the membrane proteome of NK cells is plausible but
      represents a non-core localization. The term "membrane" is very broad,
      and HSPA2's primary functional localization is cytosol and nucleus
      (synaptonemal complex in meiosis).
- term:
    id: GO:0019899
    label: enzyme binding
  evidence_type: IPI
  original_reference_id: PMID:23921388
  review:
    summary: >-
      IPI annotation of HSPA2 for enzyme binding based on its interaction with
      METTL21A (Q8WXB1, also known as HSPA-KMT) demonstrated in Jakobsson et
      al. (PMID:23921388). METTL21A was identified as the methyltransferase
      responsible for trimethylation of Lys-564 in HSPA2 and other HSP70 family
      members. The interaction was demonstrated both in vitro and in vivo, and
      the K564A mutation abolished methylation. This is a real enzyme-substrate
      interaction where HSPA2 is the substrate. However, "enzyme binding" is
      relatively uninformative; the biologically informative aspect is that
      HSPA2 is a substrate of METTL21A methyltransferase.
    action: KEEP_AS_NON_CORE
    reason: >-
      The interaction between HSPA2 and METTL21A (PMID:23921388) is real and
      well-characterized, but HSPA2 is the substrate rather than having enzyme
      binding as a core molecular function. This is a non-core annotation.
    supported_by:
      - reference_id: PMID:23921388
        supporting_text: >-
          we identified the methyltransferase METTL21A as the enzyme responsible
          for trimethylation of a conserved lysine residue found in several
          human Hsp70 (HSPA) proteins
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: PMID:21231916
  review:
    summary: >-
      IDA annotation of HSPA2 to cytosol based on Hageman et al. (PMID:21231916),
      who demonstrated cytosolic chaperone activities of HSPA2 including
      luciferase refolding and polyQ aggregation suppression. These functional
      assays were performed in the cytosol of cultured cells. This is direct
      experimental evidence for cytosolic localization and is consistent with
      the IBA annotation for the same term.
    action: ACCEPT
    reason: >-
      Cytosol localization is directly demonstrated by functional chaperone
      assays (luciferase refolding, polyQ aggregation suppression) performed
      in the cytosol (PMID:21231916). This is a core localization for HSPA2.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase and on the suppression of
          aggregation of a non-foldable polyQ (polyglutamine)-expanded
          Huntingtin fragment
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IDA
  original_reference_id: PMID:21231916
  review:
    summary: >-
      IDA annotation of HSPA2 for protein refolding based on Hageman et al.
      (PMID:21231916), who directly demonstrated that HSPA2 overexpression
      supports refolding of heat-denatured luciferase. This is direct
      experimental evidence from a systematic comparison of all mammalian
      HSP70 family members. HSPA2 was shown to be competent for luciferase
      refolding, confirming its function as a protein refolding chaperone.
    action: ACCEPT
    reason: >-
      Direct experimental evidence demonstrating HSPA2 supports luciferase
      refolding (PMID:21231916). This is a core biological process function
      of HSPA2 as an HSP70 chaperone.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IDA
  original_reference_id: PMID:21231916
  review:
    summary: >-
      Hageman et al. (PMID:21231916) systematically compared the chaperone
      activities of mammalian HSP70 family members using functional assays
      for protein refolding and aggregation suppression. The study assessed
      HSPA2 and other HSPAs for "refolding of heat-denatured luciferase"
      and "suppression of aggregation of a non-foldable polyQ-expanded
      Huntingtin fragment." These are assays of active chaperone function
      (foldase activity), not merely passive binding to unfolded substrates.
      HSPA2 was shown to support luciferase refolding and suppress protein
      aggregation, demonstrating it functions as an ATP-dependent protein
      folding chaperone. The annotation as GO:0051082 "unfolded protein
      binding" underrepresents this activity; the correct term is GO:0044183
      "protein folding chaperone." GO:0051082 is being obsoleted per
      go-ontology#30962.
    action: MODIFY
    reason: >-
      The experimental evidence from PMID:21231916 demonstrates active
      chaperone function (refolding of denatured luciferase, suppression
      of polyQ aggregation), which is GO:0044183 "protein folding chaperone"
      activity, not merely passive binding to unfolded proteins (GO:0051082).
      Furthermore, GO:0051082 is being obsoleted (go-ontology#30962) with
      GO:0044183 as the recommended replacement for foldase-type chaperones.
      HSPA2 already has an IBA annotation for GO:0044183, and the IDA evidence
      from this paper directly supports that term.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
    additional_reference_ids:
      - go-ontology#30962
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase and on the suppression of
          aggregation of a non-foldable polyQ (polyglutamine)-expanded
          Huntingtin fragment
      - reference_id: PMID:21231916
        supporting_text: >-
          even within the highly sequence-conserved HSPA family, functional
          differentiation is larger than expected
- term:
    id: GO:0090084
    label: negative regulation of inclusion body assembly
  evidence_type: IDA
  original_reference_id: PMID:21231916
  review:
    summary: >-
      IDA annotation of HSPA2 for negative regulation of inclusion body assembly
      based on Hageman et al. (PMID:21231916), who demonstrated that HSPA2
      overexpression suppresses aggregation of a polyQ-expanded Huntingtin
      fragment. This suppression of protein aggregation (inclusion body
      formation) is a direct consequence of HSPA2 chaperone activity. The
      annotation accurately describes the experimental observation that HSPA2
      can prevent inclusion body formation by maintaining client proteins in
      a soluble state.
    action: ACCEPT
    reason: >-
      Directly demonstrated by the polyQ aggregation suppression assay in
      PMID:21231916. Suppression of protein aggregation/inclusion body
      formation is a core chaperone function of HSPA2. This is a well-supported
      annotation.
    supported_by:
      - reference_id: PMID:21231916
        supporting_text: >-
          we assessed the effect of overexpression of each of these HSPs on
          refolding of heat-denatured luciferase and on the suppression of
          aggregation of a non-foldable polyQ (polyglutamine)-expanded
          Huntingtin fragment
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: HDA
  original_reference_id: PMID:21630459
  review:
    summary: >-
      HDA annotation of HSPA2 to nucleus based on proteomic characterization of
      the human sperm nucleus (PMID:21630459). HSPA2 was identified as a
      component of the sperm nucleus proteome by high-throughput mass
      spectrometry. This is consistent with HSPA2's known role in spermatogenesis
      and its association with synaptonemal complexes in the nucleus of meiotic
      spermatocytes (PMID:8622925). Nuclear localization is a well-supported
      aspect of HSPA2 biology.
    action: ACCEPT
    reason: >-
      HSPA2 was detected in the human sperm nucleus proteome (PMID:21630459),
      consistent with its role in meiotic spermatocyte nuclei where it associates
      with synaptonemal complexes (PMID:8622925). Nuclear localization is
      supported by multiple independent lines of evidence.
- term:
    id: GO:0072562
    label: blood microparticle
  evidence_type: HDA
  original_reference_id: PMID:22516433
  review:
    summary: >-
      HDA annotation of HSPA2 to blood microparticle based on proteomic analysis
      of plasma microvesicles (PMID:22516433). HSP70 proteins are commonly
      detected in extracellular vesicles and blood microparticles, likely
      reflecting their abundance and their role in extracellular signaling or
      stress response. Detection in blood microparticles is not a core
      functional localization for HSPA2.
    action: KEEP_AS_NON_CORE
    reason: >-
      Detection in blood microparticles is a common finding for abundant
      intracellular proteins in proteomics studies. This is not a core
      functional localization for HSPA2 but may reflect real biology
      (extracellular chaperone function or vesicular secretion).
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  review:
    summary: >-
      HDA annotation of HSPA2 to extracellular exosome based on large-scale
      proteomics of urinary exosomes (PMID:19056867). HSP70 family members are
      among the most commonly detected proteins in exosome proteomics studies.
      While this may reflect real biology (HSP70s have roles in exosome
      biogenesis and can be secreted), it is not a core functional localization
      for HSPA2.
    action: KEEP_AS_NON_CORE
    reason: >-
      HSP70 family members are commonly detected in exosome proteomics.
      While potentially real, extracellular exosome localization is not a core
      functional localization for HSPA2, whose primary functions are in
      cytosolic protein folding and meiotic spermatocyte biology.
- term:
    id: GO:0036128
    label: CatSper complex
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS annotation of HSPA2 as part of the CatSper complex based on manual
      transfer from mouse ortholog Hsp70-2 (P17156). UniProt states "Component
      of the CatSper complex" for HSPA2 (by similarity). CatSper is a
      sperm-specific calcium channel complex essential for sperm motility and
      hyperactivation. HSPA2 association with CatSper is consistent with its
      specialized role in spermatogenesis and sperm function. This duplicates
      the IEA annotation for the same term.
    action: KEEP_AS_NON_CORE
    reason: >-
      CatSper complex membership is supported by mouse ortholog data and
      UniProt annotation. This is a specialized sperm function annotation
      that is consistent with HSPA2's role in spermatogenesis but is a
      secondary aspect of its biology.
- term:
    id: GO:0006986
    label: response to unfolded protein
  evidence_type: TAS
  original_reference_id: PMID:7829106
  review:
    summary: >-
      TAS annotation of HSPA2 for response to unfolded protein based on
      Bonnycastle et al. (PMID:7829106), which cloned and characterized the
      HSPA2 gene. The paper describes HSPA2 as a member of the HSP70 family
      and notes its constitutive expression pattern. While the paper does not
      directly demonstrate response to unfolded protein, it characterizes HSPA2
      as an HSP70 gene family member, and HSP70 proteins are fundamentally
      involved in the unfolded protein response. The TAS evidence code is
      appropriate for this inference based on family membership.
    action: ACCEPT
    reason: >-
      HSPA2 is an HSP70 family member (PMID:7829106) and involvement in
      response to unfolded protein is a fundamental function of this family.
      The TAS annotation is appropriate given the well-established role of
      HSP70 chaperones in proteostasis.
    supported_by:
      - reference_id: PMID:7829106
        supporting_text: >-
          A genomic clone for the human heat shock protein (HSP) 70 gene
          located on chromosome 14 was isolated and sequenced. The gene,
          designated HSPA2, has a single open reading frame of 1917 bp that
          encodes a 639-amino acid protein
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: TAS
  original_reference_id: PMID:3037489
  review:
    summary: >-
      PMID:3037489 (Dworniczak and Mirault, 1987) describes the structure and
      expression of a human gene coding for a 71 kDa heat shock cognate protein.
      The paper characterizes an hsc70 gene (likely HSPA8/HSC70, not HSPA2) as
      encoding a protein "very likely to be identical to a clathrin uncoating
      ATPase recently identified as a member of the hsp70-like protein family."
      This TAS annotation to HSPA2 appears to have been made based on the general
      understanding that HSP70 family members bind unfolded proteins, but the
      paper actually describes HSPA8, not HSPA2 specifically. Regardless of
      the attribution, GO:0051082 is being obsoleted (go-ontology#30962) and
      the appropriate replacement for HSP70 foldase-type chaperones is GO:0044183
      "protein folding chaperone." HSPA2, like other HSP70 members, functions
      as an ATP-dependent foldase.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted (go-ontology#30962). The cited paper
      (PMID:3037489) describes a cognate hsc70 gene that may actually correspond
      to HSPA8 rather than HSPA2. Nonetheless, HSPA2 is a well-established
      HSP70 family member with documented foldase chaperone activity
      (PMID:21231916). The correct replacement term is GO:0044183 "protein
      folding chaperone", reflecting the active ATP-dependent protein folding
      function of HSP70 family members.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
    additional_reference_ids:
      - go-ontology#30962
      - PMID:21231916
    supported_by:
      - reference_id: PMID:3037489
        supporting_text: >-
          In all eukaryotes examined so far, hsp70 gene families include cognate
          genes (hsc70) encoding proteins of about 70 Kd which are expressed
          constitutively during normal growth and development
      - reference_id: PMID:3037489
        supporting_text: >-
          The latter is very likely to be identical to a clathrin uncoating
          ATPase recently identified as a member of the hsp70-like protein
          family
- term:
    id: GO:0007140
    label: male meiotic nuclear division
  evidence_type: TAS
  original_reference_id: PMID:8622925
  review:
    summary: >-
      TAS annotation of HSPA2 for male meiotic nuclear division based on Dix
      et al. (PMID:8622925). This landmark paper demonstrated that targeted
      disruption of the mouse Hsp70-2 gene resulted in failed meiosis in male
      germ cells. Knockout males "lacked postmeiotic spermatids and mature
      sperm" and "development rarely progressed to the meiotic divisions."
      The study concluded that "HSP70-2 participates in synaptonemal complex
      function during meiosis in male germ cells." This is a core specialized
      function of HSPA2.
    action: ACCEPT
    reason: >-
      Male meiotic nuclear division is a core specialized function of HSPA2,
      directly demonstrated by the mouse knockout study where loss of Hsp70-2
      prevented meiotic progression (PMID:8622925). This is among the most
      well-supported annotations for HSPA2.
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not
          synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm,
          and were infertile.
      - reference_id: PMID:8622925
        supporting_text: >-
          These results suggest that HSP70-2 participates in synaptonemal
          complex function during meiosis in male germ cells and is linked
          to mechanisms that inhibit apoptosis.
- term:
    id: GO:0007286
    label: spermatid development
  evidence_type: TAS
  original_reference_id: PMID:8622925
  review:
    summary: >-
      TAS annotation of HSPA2 for spermatid development based on Dix et al.
      (PMID:8622925). The mouse knockout study showed that Hsp70-2 -/- males
      "lacked postmeiotic spermatids and mature sperm." This indicates that
      HSPA2 is required for the meiotic progression that precedes spermatid
      formation. However, the study shows that meiosis fails before spermatids
      are formed, so the absence of spermatids is an indirect consequence of
      failed meiosis rather than a direct role in spermatid development per se.
      The annotation is still appropriate under TAS evidence as a reasonable
      inference from the knockout phenotype.
    action: ACCEPT
    reason: >-
      Spermatid development failure is a consequence of HSPA2/Hsp70-2 loss
      (PMID:8622925). While the primary defect is in meiotic progression,
      the resulting absence of spermatids means HSPA2 is required for this
      process. The TAS evidence code is appropriate for this inference.
    supported_by:
      - reference_id: PMID:8622925
        supporting_text: >-
          Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not
          synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm,
          and were infertile. However, neither meiosis nor fertility was
          affected in female Hsp70-2 -/- mice.
core_functions:
- description: >-
    ATP-dependent protein folding chaperone that assists in refolding of
    heat-denatured proteins and suppresses aggregation of misfolded proteins
    (including polyQ-expanded substrates) in the cytosol, through cycles of
    ATP binding, hydrolysis, and ADP release mediated by J-domain and
    nucleotide exchange factor co-chaperones. The interaction network includes
    DNAJB12, STIP1, HSPBP1, HSPA1A, HSPA8, and HSP90AA1
    (DOI:10.62347/cwpe7813). HSPA2 is also an extracellular vesicle (EV)-
    associated protein; proteotoxic stress can redistribute HSPA2 from
    intracellular pools to EVs (DOI:10.1038/s41598-023-31962-5). This
    provides a biological route for HSPA2 detection in biofluids and
    potential roles in intercellular communication.
  molecular_function:
    id: GO:0044183
    label: protein folding chaperone
  directly_involved_in:
  - id: GO:0042026
    label: protein refolding
  - id: GO:0090084
    label: negative regulation of inclusion body assembly
  - id: GO:0006986
    label: response to unfolded protein
  locations:
  - id: GO:0005829
    label: cytosol
  - id: GO:0005634
    label: nucleus
  supported_by:
  - reference_id: PMID:21231916
    supporting_text: >-
      we assessed the effect of overexpression of each of these HSPs on
      refolding of heat-denatured luciferase and on the suppression of
      aggregation of a non-foldable polyQ (polyglutamine)-expanded
      Huntingtin fragment
- description: >-
    Essential chaperone for male meiosis and spermatogenesis. Associates with
    synaptonemal complexes during meiotic prophase and localizes to the
    meiotic spindle, where it is required for meiotic progression. Loss of
    the mouse ortholog Hsp70-2 causes failed meiosis, germ cell apoptosis,
    and male infertility. HSPA2 also supports post-meiotic sperm remodeling,
    including cytoplasmic extrusion and plasma membrane remodeling required
    for zona pellucida binding competence, with reported roles in enabling
    surface relocation of proteins needed for oocyte zona interaction during
    capacitation (DOI:10.3390/ijms23126497). Quantitative enrichment of
    HSPA2-positive cells in HA-bound sperm (68.9% vs 28.6% uncapacitated;
    DOI:10.1007/s43032-022-01031-9) connects HSPA2 with sperm functional
    maturity. HSPA2 interacts with SHCBP1L to support spindle integrity
    during male meiosis (DOI:10.62347/cwpe7813). Seminal plasma HSPA2 is a
    promising non-invasive biomarker for stratification of non-obstructive
    azoospermia, with 7.3-fold higher abundance in healthy controls vs
    Sertoli cell-only phenotype (DOI:10.3389/fendo.2024.1327800).
  molecular_function:
    id: GO:0044183
    label: protein folding chaperone
  directly_involved_in:
  - id: GO:0007140
    label: male meiotic nuclear division
  - id: GO:0007283
    label: spermatogenesis
  - id: GO:0007286
    label: spermatid development
  locations:
  - id: GO:0000795
    label: synaptonemal complex
  - id: GO:0072687
    label: meiotic spindle
  - id: GO:0001673
    label: male germ cell nucleus
  supported_by:
  - reference_id: PMID:8622925
    supporting_text: >-
      Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not
      synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm,
      and were infertile.
  - reference_id: PMID:8622925
    supporting_text: >-
      These results suggest that HSP70-2 participates in synaptonemal
      complex function during meiosis in male germ cells and is linked
      to mechanisms that inhibit apoptosis.
  - reference_id: PMID:7829106
    supporting_text: >-
      HSPA2 is constitutively expressed in most tissues, with very high
      levels in testis and skeletal muscle.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:16189514
  title: Towards a proteome-scale map of the human protein-protein interaction network.
  findings: []
- id: PMID:16713569
  title: A protein-protein interaction network for human inherited ataxias and disorders
    of Purkinje cell degeneration.
  findings: []
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings: []
- id: PMID:21231916
  title: The diverse members of the mammalian HSP70 machine show distinct chaperone-like
    activities.
  findings: []
- id: PMID:21630459
  title: Proteomic characterization of the human sperm nucleus.
  findings: []
- id: PMID:22516433
  title: Proteomic analysis of microvesicles from plasma of healthy donors reveals
    high individual variability.
  findings: []
- id: PMID:23921388
  title: Identification and characterization of a novel human methyltransferase modulating
    Hsp70 protein function through lysine methylation.
  findings: []
- id: PMID:25036637
  title: A quantitative chaperone interaction network reveals the architecture of
    cellular protein homeostasis pathways.
  findings: []
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
- id: PMID:3037489
  title: Structure and expression of a human gene coding for a 71 kd heat shock 'cognate'
    protein.
  findings: []
- id: PMID:31515488
  title: Extensive disruption of protein interactions by genetic variants across the
    allele frequency spectrum in human populations.
  findings: []
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
- id: PMID:32814053
  title: Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins
    and Uncovers Widespread Protein Aggregation in Affected Brains.
  findings: []
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
- id: PMID:35271311
  title: 'OpenCell: Endogenous tagging for the cartography of human cellular organization.'
  findings: []
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
- id: PMID:7829106
  title: Cloning, sequencing, and mapping of the human chromosome 14 heat shock protein
    gene (HSPA2).
  findings: []
- id: PMID:8622925
  title: Targeted gene disruption of Hsp70-2 results in failed meiosis, germ cell
    apoptosis, and male infertility.
  findings: []
- id: DOI:10.1038/s41598-023-31962-5
  title: Heat shock protein A2 is a novel extracellular vesicle-associated protein
  findings:
  - statement: >-
      Demonstrates HSPA2 is an EV-associated protein. Proteotoxic stress (proteasome
      inhibition with bortezomib) shifts HSPA2 from intracellular pools to extracellular
      release in EVs. Validated using CRISPR/Cas9 HSPA2 knockout pools and GFP-HSPA2
      overexpression. EV mean size approximately 105.6 nm.
- id: DOI:10.3390/ijms23126497
  title: Targeted Analysis of HSP70 Isoforms in Human Spermatozoa in the Context of
    Capacitation and Motility
  findings:
  - statement: >-
      HSPA2 supports spermatogenesis and post-meiotic sperm remodeling, including
      cytoplasmic extrusion and plasma membrane remodeling required for zona pellucida
      binding competence. Roles in enabling surface relocation of proteins needed for
      oocyte zona interaction during capacitation.
- id: DOI:10.1007/s43032-022-01031-9
  title: Molecular Chaperone HSPA2 Distribution During Hyaluronic Acid Selection in
    Human Sperm
  findings:
  - statement: >-
      Quantified HSPA2 in human sperm (16 donors, approximately 19,200 sperm assessed).
      HA-bound sperm showed 68.9% HSPA2 positivity vs 28.6% uncapacitated and 22.9%
      capacitated (p<0.001). HA-bound sperm fraction was 21.4 plus/minus 7.4%.
- id: DOI:10.3389/fendo.2024.1327800
  title: Proteomic biomarkers in seminal plasma as predictors of reproductive potential
    in azoospermic men
  findings:
  - statement: >-
      Among 917 quantified proteins in seminal plasma proteomics, HSPA2 was more
      abundant in healthy controls than Sertoli cell-only phenotype (fold-change
      HC/SCO = 7.31, adjusted p=0.0217). Identifies HSPA2 as a promising
      non-invasive biomarker for spermatogenic function.
- id: DOI:10.1093/cvr/cvae181
  title: The diabetic myocardial transcriptome reveals Erbb3 and Hspa2 as novel
    biomarkers of incident heart failure
  findings:
  - statement: >-
      GTEx analysis (425 RA and 428 LV samples) showed diabetes associated with
      higher Hspa2 expression in LV myocardium. Higher circulating HSPA2 (highest
      quartile) was associated with impaired LV contractility, higher LV mass, and
      increased incident heart failure and cardiovascular death.
- id: DOI:10.62347/cwpe7813
  title: Bioinformatics analysis and alternative polyadenylation in Heat Shock Proteins
    70 (HSP70) family members
  findings:
  - statement: >-
      Lists HSPA2-associated interactors including DNAJB12, STIP1, HSPBP1, HSPA1A,
      HSPA8, HSP90AA1. Notes HSPA2 role in spermatogenesis and proposed interaction
      with SHCBP1L to support spindle integrity during male meiosis.

HSPA2

Gene Description

Existing Annotations Review

Core Functions

References

📚 Additional Documentation

Deep Research Falcon

Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

Target Gene/Protein Identity (from UniProt):

MANDATORY VERIFICATION STEPS:

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Output

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

Target Gene/Protein Identity (from UniProt):

MANDATORY VERIFICATION STEPS:

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Citations

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