SSA2

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005634 nucleus	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 nuclear localization is supported by NAS evidence from PMID:15102838 (HAP1 repressor complex). As a close paralog of SSA1 (97% identity), SSA2 is expected to share nuclear localization. SSA1 has direct IDA evidence for nuclear localization (PMID:10347213). Reason: Phylogenetically consistent. SSA2 is part of the HAP1 repressor complex in the nucleus (ComplexPortal CPX-1883). As a near-identical paralog of SSA1, nuclear localization is well-supported.
GO:0005737 cytoplasm	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 is a major cytoplasmic Hsp70. IBA is consistent with IDA evidence from PMID:8755907 and UniProt subcellular location annotation. Reason: Core localization. SSA2 is constitutively expressed and highly abundant in the cytoplasm.
GO:0005886 plasma membrane	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 has been detected at the plasma membrane by HDA (PMID:16622836). IBA is consistent. Reason: Supported by proteomics data. SSA2, like SSA1, is associated with the plasma membrane.
GO:0016887 ATP hydrolysis activity	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 has ATPase activity supported by ISS evidence from PMID:8151709. As a 97% identical paralog of SSA1, which has well-characterized ATPase activity (PMID:7737974), SSA2's ATPase activity is certain. Reason: Core molecular function. The ATPase activity drives the chaperone cycle. SSA2 is 97% identical to SSA1 whose ATPase activity is biochemically established. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md The N-terminal nucleotide-binding domain (NBD) is implicated in ATPase-cycle control (Ydj1 binds the NBD to stimulate ATPase activity).
GO:0031072 heat shock protein binding	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 interacts with numerous heat shock proteins including HSP82, HSC82, SSE1, SIS1, STI1, SBA1, and HSP26/HSP42. UniProt lists extensive IntAct interaction data. Reason: Well-supported by extensive IPI data. SSA2 physically interacts with HSP82 (4 experiments), HSC82 (3 experiments), SSE1 (4 experiments), SIS1 (5 experiments), STI1 (4 experiments), and other chaperones. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md Hsp90 (Hsp82): receives certain clients after Hsp70 processing; Ssa2 participates in upstream client handling and transfer toward Hsp90. file:yeast/SSA2/SSA2-deep-research-falcon.md Hsp40/J-domain cochaperone Ydj1: recruits misfolded clients to Hsp70 and stimulates Hsp70 ATPase activity and substrate transfer.
GO:0044183 protein folding chaperone	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 is a bona fide protein folding chaperone. PMID:8947547 demonstrated that immunodepletion of Ssa1/2p from yeast cytosol dramatically reduced refolding of denatured luciferase. PMID:9789005 showed SSA-dependent folding of newly translated OTC in vivo. Reason: Core molecular function. SSA2 is an ATP-dependent protein folding chaperone, functionally interchangeable with SSA1 for refolding activity. Supporting Evidence: PMID:8947547 Depletion of Ssa1/2p had no effect on the ability of the yeast lysate to synthesize enzymatically active luciferase, but had a dramatic effect on the ability of the lysate to refold chemically denatured luciferase. file:yeast/SSA2/SSA2-deep-research-falcon.md SSA2 encodes an ATP-dependent molecular chaperone of the Hsp70 family. Rather than catalyzing a metabolic reaction with a defined substrate/product, Ssa2 performs ATP-driven cycles of client binding and release to prevent aggregation and promote folding/refolding and quality control.
GO:0005829 cytosol	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 is primarily a cytosolic protein. IBA is consistent with IDA evidence from PMID:16806052. Reason: Core localization. SSA2 is the major cytosolic Hsp70 along with SSA1. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md Fluorescence microscopy of N-terminally tagged Ssa proteins (including Ssa2) shows predominantly diffuse signal in most cells, supporting predominant cytosolic localization under those conditions. file:yeast/SSA2/SSA2-deep-research-falcon.md Gaur et al. explicitly treat Ssa2 as one of four cytosolic Ssa Hsp70s acting in the Hsp90 pathway.
GO:0042026 protein refolding	IBA GO_REF:0000033	ACCEPT	Summary: SSA2 is directly involved in protein refolding. PMID:8947547 demonstrated that Ssa1/2p depletion dramatically reduced refolding capacity of yeast cytosol. Reason: Well-supported core function. Refolding of denatured proteins is a central activity of SSA2 as demonstrated by PMID:8947547. Supporting Evidence: PMID:8947547 These results demonstrate, for the first time, the refolding activity of Ssa1/2p in the context of the yeast cytosol, and define refolding activity as a chaperone function specific to Ssa1/2p file:yeast/SSA2/SSA2-deep-research-falcon.md Ydj1-assisted luciferase refolding activity was reported as ~25–30-fold higher with Ssa2 than with Ssa4, consistent with stronger Ydj1–Ssa2 functional coupling.
GO:0000049 tRNA binding	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: IEA annotation for tRNA binding. Consistent with IDA evidence from PMID:25853343 which demonstrated that SSA2 directly binds tRNA as part of a tRNA nuclear import system. Reason: Correct but non-core. Supported by direct experimental evidence (IDA from PMID:25853343). tRNA binding is a specialized moonlighting activity of SSA2.
GO:0000166 nucleotide binding	IEA GO_REF:0000043	ACCEPT	Summary: SSA2 binds ATP and ADP as part of its chaperone cycle. This is a parent term of ATP binding and is correct but overly general. Reason: Correct but general. More specific terms (ATP binding, ATP hydrolysis activity) are also annotated, so this broader IEA is acceptable as a redundant parent.
GO:0000329 fungal-type vacuole membrane	IEA GO_REF:0000117	ACCEPT	Summary: SSA2 localization to the vacuole membrane is supported by IDA evidence from PMID:10745074, which showed cytosolic Hsp70 involvement in aminopeptidase I transport to the vacuole. Reason: Correct. Consistent with direct experimental evidence (IDA from PMID:10745074).
GO:0005524 ATP binding	IEA GO_REF:0000120	ACCEPT	Summary: SSA2 binds ATP through its nucleotide-binding domain. This is core to its function. Also supported by IDA from PMID:10893257. Reason: Correct and fundamental. ATP binding is essential for the SSA2 chaperone cycle. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md This is evidenced in (i) biochemical handling consistent with ATP-binding Hsp70 behavior (purification via ATP-agarose and ATP elution) and (ii) mechanistic descriptions of cochaperone control of the Hsp70 ATPase cycle (Ydj1 stimulating ATPase activity and substrate transfer).
GO:0005737 cytoplasm	IEA GO_REF:0000044	ACCEPT	Summary: Duplicate of the IBA and IDA annotations for cytoplasm. Correct. Reason: Correct. Redundant with IBA and IDA annotations but acceptable.
GO:0006457 protein folding	IEA GO_REF:0000117	ACCEPT	Summary: SSA2 is directly involved in protein folding as demonstrated experimentally (IDA from PMID:7867784, IMP from PMID:9448096). IEA is consistent. Reason: Correct. Consistent with direct experimental evidence.
GO:0006616 SRP-dependent cotranslational protein targeting to membrane, translocation	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: SSA2 has been implicated in protein translocation to the ER membrane (IMP from PMID:8754838). However, PMID:8947547 found that depletion of Ssa1/2p had no effect on translocation efficiency in vitro. The role may be more indirect. Reason: Consistent with the existing IMP annotation from PMID:8754838, but this is not a core function. PMID:8947547 showed depletion had no effect on translocation efficiency in vitro, suggesting an indirect role. Supporting Evidence: PMID:8947547 Depletion of Ssa1/2p had no effect on the efficiency of translocation in this in vitro assay.
GO:0009277 fungal-type cell wall	IEA GO_REF:0000117	ACCEPT	Summary: SSA2 has been detected in the cell wall by IDA (PMID:8755907). IEA is consistent. UniProt also annotates SSA2 to the cell wall. Reason: Correct. Consistent with direct experimental evidence and UniProt annotation.
GO:0016887 ATP hydrolysis activity	IEA GO_REF:0000002	ACCEPT	Summary: Duplicate of IBA and ISS annotations. Correct InterPro-based annotation. Reason: Correct. Redundant with IBA and ISS annotations but acceptable.
GO:0033554 cellular response to stress	IEA GO_REF:0000117	ACCEPT	Summary: SSA2 is a heat shock protein involved in stress response. Although SSA2 is constitutively expressed (unlike the stress-induced SSA3/SSA4), it participates in protein quality control during stress. Reason: Correct but general. SSA2 responds to and helps manage various stresses through its chaperone activity. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md Disrupting the Hsf1-binding site in SSA2 (ssa2ΔHSE) was associated with elevated basal HSE-YFP reporter and reduced induction after prolonged heat shock, and the authors interpret the reduced induction as explained by the increased basal reporter level—consistent with SSA2 contributing to basal repression/feedback behavior in the Hsf1 regulon context.
GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: SSA2 participates in ubiquitin-dependent protein degradation. Consistent with IGI evidence from PMID:27178214. Reason: Correct but non-core. SSA2 assists in presenting misfolded substrates to the ubiquitin-proteasome system as part of its broader protein quality control role. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md SSA2 is an ATP-dependent molecular chaperone of the Hsp70 family that binds ATP and acts with Hsp40 cochaperones and nucleotide exchange factors to prevent aggregation, assist folding/refolding, and support degradation/translocation of client proteins.
GO:0051082 unfolded protein binding	IEA GO_REF:0000117	MODIFY	Summary: GO:0051082 (unfolded protein binding) is being considered for obsoletion. SSA2 does bind unfolded proteins, but this is part of its chaperone activity, not a standalone binding function. The appropriate replacement is GO:0140662 (ATP-dependent protein folding chaperone). Reason: GO:0051082 is targeted for obsoletion. SSA2 binds unfolded proteins as part of its ATP-dependent chaperone cycle. The correct annotation is GO:0140662 (ATP-dependent protein folding chaperone) or the already-present GO:0044183 (protein folding chaperone). Proposed replacements: ATP-dependent protein folding chaperone
GO:0051170 import into nucleus	IEA GO_REF:0000117	ACCEPT	Summary: SSA2 is involved in tRNA import into the nucleus (IMP from PMID:25853343, PMID:33074312). This IEA is a broader parent term consistent with the experimental evidence. Reason: Correct but general. Consistent with the more specific experimental annotation for tRNA import into nucleus.
GO:0005515 protein binding	IPI PMID:14729968 The ctf13-30/CTF13 genomic haploinsufficiency modifier scree...	MODIFY	Summary: IPI evidence from ctf13-30/CTF13 haploinsufficiency screen. SSA2 is a chaperone that binds many client proteins. Reason: Protein binding is uninformative for a chaperone that by definition binds many proteins. Better captured by GO:0044183 (protein folding chaperone). Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:15766533 Navigating the chaperone network: an integrative map of phys...	MODIFY	Summary: IPI evidence for SSA2 binding HSP82 and HSC82 from chaperone network mapping. These are well-known Hsp70-Hsp90 interactions. Reason: Protein binding is uninformative. The Hsp70-Hsp90 interaction is better captured by GO:0031072 (heat shock protein binding) which is already annotated via IBA. Proposed replacements: heat shock protein binding
GO:0005515 protein binding	IPI PMID:16284124 An integrated mass spectrometry-based proteomic approach: qu...	MODIFY	Summary: IPI evidence for SSA2 binding proteasome subunits from a proteasome interactome study. Reason: Protein binding is uninformative. The SSA2-proteasome interaction relates to its role in ubiquitin-dependent protein degradation. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:16429126 Proteome survey reveals modularity of the yeast cell machine...	MODIFY	Summary: Large-scale proteome survey (Gavin et al. 2006) identifying many SSA2 interaction partners by TAP-MS. Reason: Protein binding is uninformative for a chaperone. The interactions represent chaperone-client and chaperone-cochaperone relationships. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:16606443 Comparative analysis of Saccharomyces cerevisiae WW domains ...	MODIFY	Summary: IPI evidence from analysis of WW domain-containing proteins and their interacting partners. Reason: Protein binding is uninformative for a chaperone. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:17441508 SGT2 and MDY2 interact with molecular chaperone YDJ1 in Sacc...	MODIFY	Summary: IPI evidence for SSA2 binding SGT2 via Ydj1 co-chaperone. Reason: Protein binding is uninformative. The interaction with SGT2/Ydj1 relates to SSA2's chaperone function. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:17892321 Structure-templated predictions of novel protein interaction...	MODIFY	Summary: Structure-templated predictions of protein interactions. Reason: Protein binding is uninformative for a chaperone. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:19536198 An atlas of chaperone-protein interactions in Saccharomyces ...	MODIFY	Summary: Atlas of chaperone-protein interactions (Gong et al. 2009). Systematic mapping of SSA2 chaperone-client interactions. Reason: Protein binding is uninformative. These interactions represent chaperone-client relationships inherent to SSA2's chaperone function. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:37070168 RNA-dependent interactome allows network-based assignment of...	MODIFY	Summary: RNA-dependent interactome study. Reason: Protein binding is uninformative for a chaperone. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:37968396 The social and structural architecture of the yeast protein ...	MODIFY	Summary: Social and structural architecture of yeast protein interactome. Large-scale study. Reason: Protein binding is uninformative for a chaperone. Proposed replacements: protein folding chaperone
GO:0005515 protein binding	IPI PMID:9819422 Cns1 is an essential protein associated with the hsp90 chape...	MODIFY	Summary: IPI evidence for SSA2 binding HSP82 and CPR7 via Cns1. Reason: Protein binding is uninformative. The Ssa2-Hsp82/Cpr7 interaction is a chaperone network interaction better captured by GO:0031072. Proposed replacements: heat shock protein binding
GO:0005634 nucleus	NAS PMID:15102838 A novel mode of chaperone action: heme activation of Hap1 by...	ACCEPT	Summary: NAS annotation from ComplexPortal for SSA2 nuclear localization in context of the HAP1 repressor complex (CPX-1883). Consistent with IBA. Reason: Correct. SSA2 is present in the nucleus as part of the HAP1 repressor complex.
GO:0045892 negative regulation of DNA-templated transcription	NAS PMID:15102838 A novel mode of chaperone action: heme activation of Hap1 by...	KEEP AS NON CORE	Summary: SSA2 is part of the HAP1 transcriptional repressor complex (ComplexPortal CPX-1883) where it represses HAP1-dependent transcription in the absence of heme. Reason: Genuine but secondary function. SSA2 acts as a repressive chaperone holdase for HAP1, preventing transcriptional activation. This is not a core molecular function but rather a consequence of its chaperone activity on a specific client.
GO:0070482 response to oxygen levels	NAS PMID:15102838 A novel mode of chaperone action: heme activation of Hap1 by...	KEEP AS NON CORE	Summary: SSA2 is part of the HAP1 complex that responds to heme/oxygen levels. Reason: Secondary consequence of SSA2's role in the HAP1 repressor complex, not a core function.
GO:0070482 response to oxygen levels	NAS PMID:9632766 Molecular mechanism governing heme signaling in yeast: a hig...	KEEP AS NON CORE	Summary: Same process annotation from a different reference. PMID:9632766 describes the higher-order HAP1 complex mechanism. Reason: Duplicate process annotation for the same indirect role. SSA2 participates in oxygen/heme signaling through the HAP1 complex but this is not its core function.
GO:1903561 extracellular vesicle	IDA PMID:38711329 Thermotolerance in S. cerevisiae as a model to study extrace...	KEEP AS NON CORE	Summary: PMID:38711329 detected SSA2 in extracellular vesicles during thermotolerance studies. Reason: Genuine but peripheral localization. SSA2 in extracellular vesicles likely reflects its abundance rather than a specific targeting function.
GO:0009267 cellular response to starvation	IMP PMID:25853343 Cytosolic Hsp70 and co-chaperones constitute a novel system ...	KEEP AS NON CORE	Summary: PMID:25853343 showed SSA2 involvement in tRNA nuclear import which is regulated by nutrient status/starvation. Reason: Genuine but secondary function. The starvation response of SSA2 is related to its role in tRNA import regulation.
GO:0035719 tRNA import into nucleus	IMP PMID:33074312 A novel assay provides insight into tRNAPhe retrograde nucle...	KEEP AS NON CORE	Summary: PMID:33074312 demonstrated SSA2's role in tRNA nuclear import via mutant phenotype analysis. Reason: Genuine but specialized function. tRNA nuclear import is a moonlighting activity of SSA2 distinct from its core chaperone function.
GO:0005739 mitochondrion	HDA PMID:24769239 Quantitative variations of the mitochondrial proteome and ph...	ACCEPT	Summary: HDA evidence from mitochondrial proteome/phosphoproteome study. SSA2 was detected in mitochondrial fractions. Reason: Correct. SSA2 associates with mitochondria, consistent with IDA from PMID:16806052 and its role in protein translocation across mitochondrial membranes.
GO:0005886 plasma membrane	HDA PMID:16622836 The plasma membrane proteome of Saccharomyces cerevisiae and...	ACCEPT	Summary: HDA evidence from plasma membrane proteome study. SSA2 was detected in the plasma membrane fraction. Reason: Correct. SSA2 is associated with the plasma membrane, consistent with IBA.
GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process	IGI PMID:27178214 The requirements of yeast Hsp70 of SSA family for the ubiqui...	KEEP AS NON CORE	Summary: PMID:27178214 demonstrated SSA family requirement for ubiquitin-dependent degradation of short-lived and abnormal proteins via genetic interaction. Reason: Genuine but secondary function. SSA2 assists in presenting misfolded substrates to the ubiquitin-proteasome system as part of its broader protein quality control role.
GO:0000049 tRNA binding	IDA PMID:25853343 Cytosolic Hsp70 and co-chaperones constitute a novel system ...	KEEP AS NON CORE	Summary: PMID:25853343 demonstrated that cytosolic Hsp70 (SSA2) directly binds tRNA as part of a tRNA nuclear import system. Reason: Genuine but specialized function. tRNA binding is a moonlighting activity of SSA2 related to its role in tRNA nuclear import.
GO:0035719 tRNA import into nucleus	IMP PMID:25853343 Cytosolic Hsp70 and co-chaperones constitute a novel system ...	KEEP AS NON CORE	Summary: PMID:25853343 demonstrated SSA2's role in tRNA import into the nucleus. Reason: Genuine but specialized function. Same as the other tRNA import annotation, from a different PMID.
GO:0016887 ATP hydrolysis activity	ISS PMID:8151709 Molecular evolution of the HSP70 multigene family.	ACCEPT	Summary: ISS annotation based on molecular evolution of the HSP70 multigene family. Consistent with SSA2's function as an ATPase. Reason: Correct. SSA2 has ATPase activity essential for its chaperone cycle. Redundant with IBA but acceptable.
GO:0051082 unfolded protein binding	ISS PMID:8151709 Molecular evolution of the HSP70 multigene family.	MODIFY	Summary: GO:0051082 is targeted for obsoletion. SSA2 binds unfolded proteins as part of its ATP-dependent chaperone cycle, not as a standalone binding activity. Reason: GO:0051082 is being obsoleted. The correct replacement is GO:0140662 (ATP-dependent protein folding chaperone). SSA2 binds unfolded proteins as part of its chaperone function. Proposed replacements: ATP-dependent protein folding chaperone
GO:0000329 fungal-type vacuole membrane	IDA PMID:10745074 Cytosolic Hsp70s are involved in the transport of aminopepti...	ACCEPT	Summary: PMID:10745074 showed cytosolic Hsp70s are involved in transport of aminopeptidase I from cytoplasm into the vacuole, and SSA2 localizes to the vacuole membrane. Reason: Correct localization supported by direct experimental evidence.
GO:0005524 ATP binding	IDA PMID:10893257 The heat shock protein Ssa2p is required for import of fruct...	ACCEPT	Summary: PMID:10893257 demonstrated that SSA2 binds ATP, and this binding is required for import of fructose-1,6-bisphosphatase into Vid vesicles. Reason: Core molecular function with direct experimental evidence. Supporting Evidence: PMID:10893257 The heat shock protein Ssa2p was identified as one of the ATP binding proteins involved in FBPase import.
GO:0005737 cytoplasm	IDA PMID:8755907 Members of the Hsp70 family of proteins in the cell wall of ...	ACCEPT	Summary: PMID:8755907 identified Hsp70 family members including SSA2 in the cell wall and confirmed cytoplasmic localization. Reason: Correct core localization with direct experimental evidence.
GO:0005739 mitochondrion	IDA PMID:16806052 MMI1 (YKL056c, TMA19), the yeast orthologue of the translati...	ACCEPT	Summary: PMID:16806052 detected SSA2 in mitochondrial fractions. SSA2 likely associates with mitochondria in the context of protein import. Reason: Correct. SSA2 associates with mitochondria, consistent with HDA from PMID:24769239 and its role in maintaining precursors in import-competent conformations.
GO:0005829 cytosol	IDA PMID:16806052 MMI1 (YKL056c, TMA19), the yeast orthologue of the translati...	ACCEPT	Summary: PMID:16806052 confirmed SSA2 cytosolic localization. Reason: Correct core localization. SSA2 is predominantly cytosolic.
GO:0006457 protein folding	IDA PMID:7867784 Cooperation of the molecular chaperone Ydj1 with specific Hs...	ACCEPT	Summary: Direct assay demonstrating SSA2 involvement in protein folding. Reason: Core biological process. Direct experimental demonstration of SSA2's role in protein folding. Supporting Evidence: file:yeast/SSA2/SSA2-deep-research-falcon.md Using v-Src as an Hsp90 client, Gaur et al. show that the Hsp40 cochaperone Ydj1 binds misfolded client, recruits it to Hsp70, and transfers it preferentially to Ssa2 (relative to Ssa4). Transfer to Ssa2 supports subsequent engagement with Hsp90 and client maturation.
GO:0006457 protein folding	IMP PMID:9448096 Role of Hsp70 subfamily, Ssa, in protein folding in yeast ce...	ACCEPT	Summary: PMID:9448096 showed that ssa1ssa2 mutants had significantly lower luciferase activity than wild type, demonstrating SSA proteins are needed for folding of proteins. The reduced folding capacity in ssa1ssa2 cells closely correlated with the amount of Ssa proteins present. Reason: Core biological process. Mutant phenotype demonstrates SSA2 (with SSA1) is required for protein folding in vivo. Supporting Evidence: PMID:9448096 The luciferase activity was significantly lower in ssa1ssa2 transformants than in the wild type (wt) cell transformed with the same plasmid PMID:9448096 It is suggested that constitutional Ssa "chaperones" are needed for the folding of proteins and, in cells lacking Ssa1 and Ssa2, the increased Ssa4 is thought to partly compensate for their role in the folding of luciferase in vivo
GO:0006616 SRP-dependent cotranslational protein targeting to membrane, translocation	IMP PMID:8754838 Functional interaction of cytosolic hsp70 and a DnaJ-related...	KEEP AS NON CORE	Summary: PMID:8754838 showed that SSA-deficient mutants (ssa1ts ssa2 ssa3 ssa4) had translocation defects for prepro-alpha-factor and proteinase A. However, PMID:8947547 later showed depletion of Ssa1/2p had no effect on translocation efficiency in vitro. Reason: The direct role in SRP-dependent translocation is debated. PMID:8947547 showed depletion did not affect translocation efficiency. The in vivo phenotype from PMID:8754838 may reflect SSA2's general chaperone function keeping precursors translocation-competent. Supporting Evidence: PMID:8754838 Of six proteins destined for the endoplasmic reticulum, the translocation of only prepro-alpha-factor and proteinase A was inhibited. PMID:8947547 Depletion of Ssa1/2p had no effect on the efficiency of translocation in this in vitro assay.
GO:0009277 fungal-type cell wall	IDA PMID:8755907 Members of the Hsp70 family of proteins in the cell wall of ...	ACCEPT	Summary: PMID:8755907 directly identified SSA2 as a cell wall protein. UniProt also annotates SSA2 subcellular location as "Secreted, cell wall." Reason: Correct localization. SSA2 is present in the cell wall.
GO:0051082 unfolded protein binding	IGI PMID:9789005 Folding in vivo of a newly translated yeast cytosolic enzyme...	MODIFY	Summary: PMID:9789005 showed that the SSA class of Hsp70 proteins assists folding of newly translated OTC in vivo. The IGI evidence comes from genetic interaction among SSA family members. GO:0051082 is targeted for obsoletion. Reason: GO:0051082 is being obsoleted. PMID:9789005 actually demonstrates chaperone activity, not mere binding. The correct replacement is GO:0140662 (ATP-dependent protein folding chaperone). Proposed replacements: ATP-dependent protein folding chaperone Supporting Evidence: PMID:9789005 yeast cytosolic OTC is assisted to its native state by the SSA class of yeast cytosolic Hsp70 proteins
GO:0140662 ATP-dependent protein folding chaperone	IDA PMID:8947547 The refolding activity of the yeast heat shock proteins Ssa1...	NEW	Summary: SSA2 is an ATP-dependent protein folding chaperone. PMID:8947547 demonstrated that Ssa1/2p depletion dramatically reduced refolding of denatured luciferase in yeast cytosol, and PMID:9789005 showed SSA-dependent folding of newly translated OTC. GO:0140662 is the most specific and accurate MF term, replacing the obsoleting GO:0051082. UniProt already assigns this via InterPro (IEA). Reason: GO:0140662 (ATP-dependent protein folding chaperone) is the most specific and accurate molecular function term for SSA2. It replaces the obsoleting GO:0051082 and is more specific than GO:0044183. Supporting Evidence: PMID:8947547 These results demonstrate, for the first time, the refolding activity of Ssa1/2p in the context of the yeast cytosol PMID:9789005 yeast cytosolic OTC is assisted to its native state by the SSA class of yeast cytosolic Hsp70 proteins

Core Functions

SSA2 is the most abundant cytoplasmic Hsp70 in S. cerevisiae (364,000 molecules/cell), functioning as an ATP-dependent protein folding chaperone. It is 97% identical to SSA1 and functionally interchangeable for refolding of denatured proteins (PMID:8947547). SSA2 uses ATP hydrolysis cycles to assist both de novo folding of newly translated proteins (PMID:9789005) and refolding of stress-denatured proteins (PMID:8947547, PMID:9448096). It cooperates with J-domain co-chaperones (Ydj1, Sis1), nucleotide exchange factors (Sse1/Sse2, Fes1), and Hsp90 (HSP82/HSC82). SSA2 also has specialized roles in tRNA nuclear import (PMID:25853343), ubiquitin-dependent protein degradation (PMID:27178214), and transcriptional regulation via the HAP1 repressor complex (PMID:15102838).

Molecular Function:

ATP-dependent protein folding chaperone

Directly Involved In:

protein folding protein refolding

Cellular Locations:

cytosol

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

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:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:7867784

Cooperation of the molecular chaperone Ydj1 with specific Hsp70 homologs to suppress protein aggregation.

Ydj1 cooperated with Ssa Hsp70 proteins in the prevention of protein aggregation

"Ydj1p cooperated with Ssa Hsp70 proteins in the prevention of protein aggregation, but not with the Ssb Hsp70 proteins."

PMID:8151709

Molecular evolution of the HSP70 multigene family.

ISS-based annotation of ATPase and unfolded protein binding for SSA2

"The Saccharomyces cerevisiae HSP70 family is comprised of eight members"

PMID:8754838

Functional interaction of cytosolic hsp70 and a DnaJ-related protein, Ydj1p, in protein translocation in vivo.

SSA-deficient mutants show translocation defects for specific ER-targeted proteins

"Of six proteins destined for the endoplasmic reticulum, the translocation of only prepro-alpha-factor and proteinase A was inhibited"

PMID:8755907

Members of the Hsp70 family of proteins in the cell wall of Saccharomyces cerevisiae.

Identified SSA2 in the cell wall and confirmed cytoplasmic localization

"the heat shock protein 70 (Hsp70) products of these genes, previously thought to be restricted to the cell interior, are also present in the cell wall"

PMID:8947547

The refolding activity of the yeast heat shock proteins Ssa1 and Ssa2 defines their role in protein translocation.

Demonstrated Ssa1/2 refolding activity with denatured luciferase
Found Ssa1/2 depletion does not affect translocation in vitro

PMID:9448096

Role of Hsp70 subfamily, Ssa, in protein folding in yeast cells, seen in luciferase-transformed ssa mutants.

Demonstrated SSA proteins are needed for protein folding in vivo

PMID:9632766

Molecular mechanism governing heme signaling in yeast: a higher-order complex mediates heme regulation of the transcriptional activator HAP1.

Described the HAP1 higher-order complex mechanism with Hsp70

PMID:9789005

Folding in vivo of a newly translated yeast cytosolic enzyme is mediated by the SSA class of cytosolic yeast Hsp70 proteins.

SSA class Hsp70s assist de novo folding of newly translated cytosolic enzymes

PMID:9819422

Cns1 is an essential protein associated with the hsp90 chaperone complex in Saccharomyces cerevisiae that can restore cyclophilin 40-dependent functions in cpr7Delta cells.

SSA2 associates with the Hsp90 chaperone complex via Cns1/Cpr7

PMID:10745074

Cytosolic Hsp70s are involved in the transport of aminopeptidase 1 from the cytoplasm into the vacuole.

SSA2 involved in Ape1 transport to vacuole and localizes to vacuole membrane

PMID:10893257

The heat shock protein Ssa2p is required for import of fructose-1,6-bisphosphatase into Vid vesicles.

SSA2 binds ATP and is required for FBPase import into Vid vesicles

PMID:14562106

Global analysis of protein expression in yeast.

SSA2 present at 364,000 molecules/cell in log phase

PMID:14729968

The ctf13-30/CTF13 genomic haploinsufficiency modifier screen identifies the yeast chromatin remodeling complex RSC, which is required for the establishment of sister chromatid cohesion.

PMID:15102838

A novel mode of chaperone action: heme activation of Hap1 by enhanced association of Hsp90 with the repressed Hsp70-Hap1 complex.

SSA2 is part of the HAP1 repressor complex (CPX-1883)

PMID:15766533

Navigating the chaperone network: an integrative map of physical and genetic interactions mediated by the hsp90 chaperone.

Mapped SSA2 interactions with Hsp90 chaperone network

PMID:16284124

An integrated mass spectrometry-based proteomic approach: quantitative analysis of tandem affinity-purified in vivo cross-linked protein complexes (QTAX) to decipher the 26 S proteasome-interacting network.

SSA2 interacts with the 26S proteasome

PMID:16429126

Proteome survey reveals modularity of the yeast cell machinery.

Large-scale TAP-MS identifying numerous SSA2 interactors

PMID:16606443

Comparative analysis of Saccharomyces cerevisiae WW domains and their interacting proteins.

PMID:16622836

The plasma membrane proteome of Saccharomyces cerevisiae and its response to the antifungal calcofluor.

SSA2 detected in the plasma membrane proteome

PMID:16806052

MMI1 (YKL056c, TMA19), the yeast orthologue of the translationally controlled tumor protein (TCTP) has apoptotic functions and interacts with both microtubules and mitochondria.

SSA2 detected in cytosol and mitochondrial fractions

PMID:17441508

SGT2 and MDY2 interact with molecular chaperone YDJ1 in Saccharomyces cerevisiae.

SSA2 interacts with SGT2 via Ydj1 co-chaperone

PMID:17892321

Structure-templated predictions of novel protein interactions from sequence information.

PMID:19536198

An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications to protein folding pathways in the cell.

Systematic mapping of SSA2 chaperone-client interactions

PMID:24769239

Quantitative variations of the mitochondrial proteome and phosphoproteome during fermentative and respiratory growth in Saccharomyces cerevisiae.

SSA2 detected in mitochondrial fraction

PMID:25853343

Cytosolic Hsp70 and co-chaperones constitute a novel system for tRNA import into the nucleus.

SSA2 binds tRNA and facilitates its import into the nucleus

PMID:27178214

The requirements of yeast Hsp70 of SSA family for the ubiquitin-dependent degradation of short-lived and abnormal proteins.

SSA family required for ubiquitin-dependent degradation

PMID:33074312

A novel assay provides insight into tRNAPhe retrograde nuclear import and re-export in S. cerevisiae.

SSA2 role in tRNA nuclear import

"the Hsp70 protein Ssa2 mediates import specifically in the latter"

PMID:37070168

RNA-dependent interactome allows network-based assignment of RNA-binding protein function.

PMID:37968396

The social and structural architecture of the yeast protein interactome.

PMID:38711329

Thermotolerance in S. cerevisiae as a model to study extracellular vesicle biology.

SSA2 detected in extracellular vesicles

PMID:12761219

Candida albicans Ssa1/2p is the cell envelope binding protein for human salivary histatin 5.

SSA2 binds human histatin 5 and mediates its fungicidal activity

file:yeast/SSA2/SSA2-deep-research-falcon.md

Falcon deep research report on SSA2 (Saccharomyces cerevisiae, UniProt P10592/YLL024C)

SSA2 (YLL024C) encodes Ssa2, a cytosolic Hsp70 (Stress-Seventy subfamily A) chaperone; it is one of four cytosolic Ssa isoforms (Ssa1-4), with Ssa1/Ssa2 constitutively expressed and Ssa3/Ssa4 stress-inducible.

"In the retrieved literature, SSA2 is consistently described as one of four cytosolic Ssa Hsp70 isoforms (Ssa1–4), with **Ssa1/Ssa2 constitutively expressed** and **Ssa3/Ssa4 stress-inducible**, matching the UniProt-provided identity and family assignment."
SSA2 is an ATP-dependent molecular chaperone of the Hsp70 family that performs ATP-driven cycles of client binding and release to prevent aggregation and promote folding/refolding and quality control, rather than catalyzing a metabolic reaction.

"**SSA2 encodes an ATP-dependent molecular chaperone of the Hsp70 family.** Rather than catalyzing a metabolic reaction with a defined substrate/product, Ssa2 performs **ATP-driven cycles of client binding and release** to prevent aggregation and promote folding/refolding and quality control."
The N-terminal nucleotide-binding domain (NBD) mediates ATPase-cycle control (the Hsp40 cochaperone Ydj1 binds the NBD to stimulate ATPase activity), while the C-terminal region contributes to substrate transfer and isoform specificity.

"The **N-terminal nucleotide-binding domain (NBD)** is implicated in ATPase-cycle control (Ydj1 binds the NBD to stimulate ATPase activity)."
SSA2 functions within the Hsp70-Hsp90 chaperone pathway; Ydj1 recruits misfolded clients to Hsp70 and transfers them preferentially to Ssa2 (over Ssa4), supporting subsequent Hsp90 engagement and client maturation.

"Using v-Src as an Hsp90 client, Gaur et al. show that the Hsp40 cochaperone **Ydj1 binds misfolded client, recruits it to Hsp70, and transfers it preferentially to Ssa2** (relative to Ssa4). Transfer to Ssa2 supports subsequent engagement with Hsp90 and client maturation."
Ssa isoforms are not fully redundant; Ydj1-assisted luciferase refolding was ~25-30-fold higher with Ssa2 than with Ssa4, reflecting stronger Ydj1-Ssa2 functional coupling.

"Ydj1-assisted luciferase refolding activity was reported as **~25–30-fold higher with Ssa2 than with Ssa4**, consistent with stronger Ydj1–Ssa2 functional coupling."
Ssa2 is localized predominantly to the cytosol; tagged Ssa proteins including Ssa2 show predominantly diffuse cytosolic distribution by fluorescence microscopy.

"Fluorescence microscopy of N-terminally tagged Ssa proteins (including **Ssa2**) shows predominantly **diffuse** signal in most cells, supporting predominant **cytosolic localization** under those conditions."
Ssa1/Ssa2 are required for formation/localization of the cytoplasmic JUNQ compartment adjacent to the nucleus-vacuole junction (NVJ) and for degradation of cytoplasmic misfolded proteins routed there; loss of both shifts handling toward peripheral IPOD-like inclusions and inhibits clearance of a misfolded reporter.

"Ssa1/Ssa2 are required for formation/localization of the cytoplasmic **JUNQ** compartment adjacent to the **nucleus–vacuole junction (NVJ)** and for degradation of cytoplasmic misfolded proteins that are routed there."
In a 2024 heat-shock-response feedback study, SSA2 had the highest expression rank among SSA paralogs (Ssa3 < Ssa4 < Ssa1 < Ssa2), and deleting its Hsf1-binding site (ssa2-deltaHSE) elevated basal HSE-YFP reporter and reduced heat-shock induction, consistent with SSA2 contributing to basal repression/feedback of the Hsf1 regulon.

"Disrupting the Hsf1-binding site in SSA2 (**ssa2ΔHSE**) was associated with **elevated basal HSE-YFP reporter** and **reduced induction after prolonged heat shock**, and the authors interpret the reduced induction as explained by the increased basal reporter level—consistent with SSA2 contributing to basal repression/feedback behavior in the Hsf1 regulon context."

Deep Research

Falcon

(SSA2-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 16 citations 2 artifacts 2026-05-30T17:43:35.651057

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000014 Figures 2, 4, and 5 contain the requested information regarding NES-LuciTs localization and the effects of specific gene deletions: (image/png)

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.

Research report: Functional annotation of Saccharomyces cerevisiae SSA2 (UniProt P10592; YLL024C)

0) Target verification (mandatory)

The gene/protein addressed here is SSA2 (YLL024C) from Saccharomyces cerevisiae (S288c), encoding Ssa2, a cytosolic Hsp70 (Stress-Seventy subfamily A) chaperone. In the retrieved literature, SSA2 is consistently described as one of four cytosolic Ssa Hsp70 isoforms (Ssa1–4), with Ssa1/Ssa2 constitutively expressed and Ssa3/Ssa4 stress-inducible, matching the UniProt-provided identity and family assignment. No conflicting “SSA2” identities (other organisms/proteins) were encountered in the analyzed corpus. (gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 1-1, gaur2020theyeasthsp70 pages 1-2)

1) Key concepts and definitions (current understanding)

1.1 What SSA2 encodes (primary function)

SSA2 encodes an ATP-dependent molecular chaperone of the Hsp70 family. Rather than catalyzing a metabolic reaction with a defined substrate/product, Ssa2 performs ATP-driven cycles of client binding and release to prevent aggregation and promote folding/refolding and quality control. This is evidenced in (i) biochemical handling consistent with ATP-binding Hsp70 behavior (purification via ATP-agarose and ATP elution) and (ii) mechanistic descriptions of cochaperone control of the Hsp70 ATPase cycle (Ydj1 stimulating ATPase activity and substrate transfer). (gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 9-9, matveenko2025optimizationofconditions pages 1-3)

1.2 Canonical Hsp70 machine components relevant to SSA2

The evidence base emphasizes that Ssa2 functions as part of a chaperone system:
- Hsp40/J-domain cochaperone Ydj1: recruits misfolded clients to Hsp70 and stimulates Hsp70 ATPase activity and substrate transfer. (gaur2020theyeasthsp70 pages 12-13, gaur2020theyeasthsp70 pages 9-9)
- Hsp90 (Hsp82): receives certain clients after Hsp70 processing; Ssa2 participates in upstream client handling and transfer toward Hsp90. (gaur2020theyeasthsp70 pages 12-13, gaur2020theyeasthsp70 pages 1-1)
- Isoform specialization within cytosolic Ssa Hsp70s: although homologous, Ssa isoforms are not fully redundant; Ssa2 can differ from Ssa4 in client maturation contexts and prion propagation phenotypes. (gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 12-13)

1.3 Domain-level functional mapping (alignment with UniProt domain architecture)

The provided evidence supports Hsp70’s division of labor between regions:
- The N-terminal nucleotide-binding domain (NBD) is implicated in ATPase-cycle control (Ydj1 binds the NBD to stimulate ATPase activity). (gaur2020theyeasthsp70 pages 13-14)
- Functional differences between Ssa2 and Ssa4 in an Hsp90-client context map strongly to the C-terminal region, which is also implicated in substrate transfer and isoform specificity. (gaur2020theyeasthsp70 pages 13-14, gaur2020theyeasthsp70 pages 1-1)

2) Cellular localization and where SSA2 acts

Direct evidence in the corpus places Ssa2 primarily in the cytosol, consistent with its classification as a cytosolic Ssa Hsp70:
- Gaur et al. explicitly treat Ssa2 as one of four cytosolic Ssa Hsp70s acting in the Hsp90 pathway. (gaur2020theyeasthsp70 pages 1-1, gaur2020theyeasthsp70 pages 1-2)
- Fluorescence microscopy of N-terminally tagged Ssa proteins (including Ssa2) shows predominantly diffuse signal in most cells, supporting predominant cytosolic localization under those conditions. (matveenko2025optimizationofconditions pages 7-9)

In addition, recent work connects Ssa1/Ssa2 activity to spatial protein quality control compartments at the cytoplasm–organelle interface:
- Ssa1/Ssa2 are required for formation/localization of the cytoplasmic JUNQ compartment adjacent to the nucleus–vacuole junction (NVJ) and for degradation of cytoplasmic misfolded proteins that are routed there. (rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 12-13)

3) Pathways and biological processes involving SSA2

3.1 Hsp70–Hsp90 client processing and maturation

A detailed mechanistic model for Ssa2 in a client maturation pathway comes from an Hsp90-client system:
- Using v-Src as an Hsp90 client, Gaur et al. show that the Hsp40 cochaperone Ydj1 binds misfolded client, recruits it to Hsp70, and transfers it preferentially to Ssa2 (relative to Ssa4). Transfer to Ssa2 supports subsequent engagement with Hsp90 and client maturation. (gaur2020theyeasthsp70 pages 12-13)
- Although Ssa2 and Ssa4 bind Hsp90 similarly, the key discriminant is weaker Ydj1 interaction with Ssa4, reducing Ydj1-assisted folding/transfer efficiency and lowering client maturation efficiency when Ssa4 is the sole Ssa. (gaur2020theyeasthsp70 pages 9-9, gaur2020theyeasthsp70 pages 1-1)

3.2 Heat shock response (HSR) feedback control involving SSA2 (2024 development)

A 2024 preprint directly interrogates gene-by-gene contributions to HSR feedback:
- Among SSA paralogs in that dataset, expression rank was reported as Ssa3 < Ssa4 < Ssa1 < Ssa2, placing SSA2 highest among SSA paralogs measured. (garde2024feedbackcontrolof pages 4-7)
- Disrupting the Hsf1-binding site in SSA2 (ssa2ΔHSE) was associated with elevated basal HSE-YFP reporter and reduced induction after prolonged heat shock, and the authors interpret the reduced induction as explained by the increased basal reporter level—consistent with SSA2 contributing to basal repression/feedback behavior in the Hsf1 regulon context. The study reports significance testing for reporter changes after 4 h heat shock (p < 0.05; two-tailed t-test) and identifies ssa2ΔHSE among specific mutants with these reporter phenotypes. (garde2024feedbackcontrolof pages 4-7)

3.3 Spatial proteostasis: JUNQ/IPOD sorting and microautophagy-linked clearance (2024 review)

Rolli et al. (2024) synthesize and extend evidence for how misfolded proteins are sorted and cleared:
- Ssa1/Ssa2 requirement: loss of Ssa1 and Ssa2 together shifts cytoplasmic misfolded-protein handling away from perinuclear JUNQ sorting and toward a peripheral, IPOD-like inclusion; the double deletion inhibits clearance of a misfolded cytosolic reporter (NES-LuciTs) and produces inclusions with limited FRAP recovery (static behavior). (rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 5-7)
- Sorting factors: sequestrase Btn2 is required for perinuclear foci (JUNQ-like), whereas Hsp42 promotes peripheral foci (IPOD-like); genetic deletions bias the reporter localization accordingly. (rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 7-9)
- Clearance mechanism: components associated with piecemeal microautophagy of the nucleus (PMN) and NVJ structure—Atg1, Atg8, Nvj1, Vac8—are implicated in JUNQ formation/clearance; Atg1 or Atg8 deletion decreases reporter clearance compared to wild type. Proteasome inhibition with 50 μM bortezomib did not show a strong effect on degradation of the cytoplasmic NES-LuciTs reporter in the described assay conditions, supporting a vacuole/autophagy-linked route for that substrate. (rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 1-2)

4) Recent developments (prioritizing 2023–2024)

The most SSA2-relevant 2023–2024 developments captured in the retrieved set are:
1. HSR systems-level feedback dissection: SSA2 emerges as (i) highly expressed relative to other SSA paralogs in a reporter dataset and (ii) a locus where deleting the Hsf1 binding site changes basal and induced Hsf1 reporter output, supporting models in which Hsp70-family expression shapes negative feedback and basal repression dynamics. (Publication date: 2024-01; URL: https://doi.org/10.1101/2024.01.09.574867) (garde2024feedbackcontrolof pages 4-7)
2. Spatial quality control emphasis: a 2024 JUNQ-focused synthesis identifies Ssa1/Ssa2 as required for JUNQ localization to NVJ and degradation of cytosolic misfolded proteins, integrating Hsp70 function with NVJ/microautophagy factors (Atg1/Atg8; Nvj1/Vac8) and sorting factors (Btn2/Hsp42). (Publication date: 2024-08; URL: https://doi.org/10.3389/fmolb.2024.1427542) (rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 12-13)

5) Current applications and real-world implementations

Within the provided evidence, SSA2’s “applications” are primarily as a core tool gene/protein in experimental and engineering workflows around proteostasis:
- Client maturation pathway dissection: SSA2 is used as a defined isoform background (including chimeras between Ssa2 and Ssa4) to map determinants of Hsp70 isoform specificity in the Hsp90 pathway and to understand how cochaperones (Ydj1) route clients through the Hsp70→Hsp90 pipeline. (gaur2020theyeasthsp70 pages 12-13, gaur2020theyeasthsp70 pages 13-14)
- Proteostasis compartment assays: the Ssa1/Ssa2 requirement for JUNQ routing and clearance makes SSA2 relevant for modeling cytosolic proteotoxic stress management, including imaging (localization, FRAP) and biochemical clearance assays (time-course Western blot). (rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 5-7)
- Recombinant production and localization validation: constructs expressing tagged SSA2 were used to optimize cytosolic Hsp70 production in yeast and confirm a largely cytosolic distribution, supporting practical purification/biochemical study pipelines. (Publication date: 2025-06; URL: https://doi.org/10.17816/ecogen676918) (matveenko2025optimizationofconditions pages 7-9)

6) Expert opinions / analysis from authoritative sources (within the retrieved evidence)

Isoform specialization is functionally meaningful: despite high homology among Ssa paralogs, Gaur et al. emphasize that isoforms can be functionally distinct in defined pathways (Hsp90 client maturation), and map those distinctions to specific regions (C-terminal determinants) and cochaperone affinities (Ydj1). This positions SSA2 not as a generic “redundant” Hsp70 but as an isoform with measurable pathway-specific capabilities. (gaur2020theyeasthsp70 pages 13-14, gaur2020theyeasthsp70 pages 9-9, gaur2020theyeasthsp70 pages 1-1)
Proteostasis is spatially organized and chaperone-dependent: Rolli et al. frame Ssa1/Ssa2 as required components that help determine whether cytosolic misfolded proteins are routed to JUNQ vs IPOD and whether they are cleared efficiently, integrating Hsp70 function into emerging models where subcellular localization (NVJ proximity) links to clearance route (microautophagy-associated processes). (rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 12-13)

7) Statistics and quantitative data (from cited studies)

Key quantitative points directly extractable from the evidence include:
- ~25–30× difference: Ydj1-assisted luciferase refolding activity was reported as ~25–30-fold higher with Ssa2 than with Ssa4, consistent with stronger Ydj1–Ssa2 functional coupling. (Gaur et al., 2020-07; https://doi.org/10.1534/genetics.120.303190) (gaur2020theyeasthsp70 pages 13-14)
- HSR reporter statistics: after 4 h heat shock, the HSR feedback study reports groups of ΔHSE mutants with significantly increased/decreased HSE-YFP relative to wild type (p < 0.05, two-tailed t-test) and identifies ssa2ΔHSE among those with elevated basal HSE-YFP and reduced inducibility. (Garde et al., 2024-01; https://doi.org/10.1101/2024.01.09.574867) (garde2024feedbackcontrolof pages 4-7)
- Proteostasis clearance assays: JUNQ/IPOD work reports significant differences in quantified degradation/phenotypes in certain comparisons (P = 0.0061 and P = 0.0392; unpaired t-tests) in time-course/clearance measurements, and notes that one cytosolic reporter (NES-VHL) cleared in about half the time of another (NES-Luci). (Rolli et al., 2024-08; https://doi.org/10.3389/fmolb.2024.1427542) (rolli2024clearingthejunq pages 7-9, rolli2024clearingthejunq pages 12-13)

8) Visual evidence (figures)

Rolli et al. (2024) figures provide visual support for SSA2-relevant claims: the requirement for Ssa1/Ssa2 in JUNQ formation and routing, Btn2/Hsp42 sorting effects, and the involvement of Atg1/Atg8 in clearance are shown in cropped figure panels retrieved from the paper. (rolli2024clearingthejunq media fa7c60b5, rolli2024clearingthejunq media b834e7ef, rolli2024clearingthejunq media 33462aaf)

9) Evidence map (compact)

The following table is an evidence-mapped summary of SSA2 functional annotation from the retrieved corpus.

Aspect	Evidence summary	Key source(s) with year, URL, and context citation IDs
identity/domains	SSA2 matches the target protein as a Saccharomyces cerevisiae cytosolic Ssa Hsp70 and is one of four SSA-family Hsp70 isoforms (Ssa1–4); Ssa1/2 are constitutive, whereas Ssa3/4 are stress inducible. Hsp70 functional architecture is supported by evidence that the N-terminal nucleotide-binding domain (NBD) mediates ATPase regulation and the C-terminal region contributes to substrate transfer/isoform specificity; the cited work maps functional distinction between Ssa2 and Ssa4 largely to the C-terminal domain. (gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 13-14, gaur2020theyeasthsp70 pages 1-1, gaur2020theyeasthsp70 pages 1-2)	Gaur et al., 2020, Genetics, https://doi.org/10.1534/genetics.120.303190 (gaur2020theyeasthsp70 pages 13-14, gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 1-1, gaur2020theyeasthsp70 pages 1-2)
biochemical activity	SSA2 is an ATP-dependent molecular chaperone of the Hsp70 family that binds ATP and acts with Hsp40 cochaperones and nucleotide exchange factors to prevent aggregation, assist folding/refolding, and support degradation/translocation of client proteins. Experimental handling of purified Ssa2 with ATP-agarose and mechanistic interpretation of Ydj1 action support ATP-linked chaperone cycling rather than enzyme-like substrate conversion. (gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 9-9, matveenko2025optimizationofconditions pages 9-10, matveenko2025optimizationofconditions pages 1-3)	Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (gaur2020theyeasthsp70 pages 2-3, gaur2020theyeasthsp70 pages 9-9); Matveenko et al., 2025, https://doi.org/10.17816/ecogen676918 (matveenko2025optimizationofconditions pages 9-10, matveenko2025optimizationofconditions pages 1-3)
localization	The strongest direct localization evidence in the provided context places SSA2 in the cytosol. Tagged Ssa proteins, including Ssa2, showed a predominantly diffuse cytosolic distribution in fluorescence microscopy, and Gaur et al. also describe SSA2 as a cytosolic Hsp70 acting upstream of Hsp90. (gaur2020theyeasthsp70 pages 1-1, gaur2020theyeasthsp70 pages 1-2, matveenko2025optimizationofconditions pages 7-9)	Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (gaur2020theyeasthsp70 pages 1-1, gaur2020theyeasthsp70 pages 1-2); Matveenko et al., 2025, https://doi.org/10.17816/ecogen676918 (matveenko2025optimizationofconditions pages 7-9)
pathways/complexes	SSA2 functions in the Hsp70–Hsp90 chaperone pathway, where Ydj1 recruits misfolded clients to Hsp70 and promotes transfer toward Hsp90-dependent maturation; Ssa2 supports this process better than Ssa4. In proteostasis compartment biology, Ssa1/Ssa2 are required for JUNQ sorting/localization to the nucleus–vacuole junction (NVJ) and for clearance of cytoplasmic misfolded proteins, with Btn2 favoring JUNQ sorting, Hsp42 favoring IPOD sorting, and Atg1/Atg8 plus Nvj1/Vac8 implicated in JUNQ clearance via microautophagy-related mechanisms. (gaur2020theyeasthsp70 pages 12-13, gaur2020theyeasthsp70 pages 9-9, rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 7-9, rolli2024clearingthejunq pages 5-7)	Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (gaur2020theyeasthsp70 pages 12-13, gaur2020theyeasthsp70 pages 9-9); Rolli et al., 2024, Front. Mol. Biosci., https://doi.org/10.3389/fmolb.2024.1427542 (rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 7-9, rolli2024clearingthejunq pages 5-7)
recent 2023-2024 findings	In a 2024 heat-shock feedback study, SSA2 had the highest expression rank among SSA paralogs in the reported reporter dataset (Ssa3 < Ssa4 < Ssa1 < Ssa2), and deleting the Hsf1-binding site at SSA2 altered Hsf1 reporter behavior, consistent with SSA2 contributing to basal repression/feedback control of Hsf1-regulated heat-shock expression. A separate 2024 study showed that loss of Ssa1/Ssa2 shifts cytoplasmic misfolded-protein management away from JUNQ and toward IPOD-like inclusions, linking SSA2 to modern models of spatial proteostasis. (garde2024feedbackcontrolof pages 4-7, rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 7-9)	Garde et al., 2024, bioRxiv, https://doi.org/10.1101/2024.01.09.574867 (garde2024feedbackcontrolof pages 4-7); Rolli et al., 2024, https://doi.org/10.3389/fmolb.2024.1427542 (rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 1-2, rolli2024clearingthejunq pages 7-9)
quantitative/statistical data	Quantitative findings in the provided context include: Ydj1-assisted luciferase refolding was ~25–30× higher with Ssa2 than Ssa4 in the Hsp90-client study; in the heat-shock feedback study, six ΔHSE mutants had significantly increased and three had significantly reduced HSE-YFP after 4 h heat shock (p < 0.05), with ssa2ΔHSE among mutants showing elevated basal reporter signal; and in JUNQ studies, NES-LuciTs degradation phenotypes showed significant differences (P = 0.0061 and P = 0.0392 in unpaired t-tests), while 50 μM bortezomib did not significantly alter NES-LuciTs degradation in one assay and NES-VHL cleared in about half the time of NES-Luci. (gaur2020theyeasthsp70 pages 13-14, garde2024feedbackcontrolof pages 4-7, rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 7-9)	Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (gaur2020theyeasthsp70 pages 13-14); Garde et al., 2024, https://doi.org/10.1101/2024.01.09.574867 (garde2024feedbackcontrolof pages 4-7); Rolli et al., 2024, https://doi.org/10.3389/fmolb.2024.1427542 (rolli2024clearingthejunq pages 12-13, rolli2024clearingthejunq pages 7-9)
applications	Within the provided evidence, SSA2 is most useful as a model proteostasis factor for dissecting client maturation, stress-response feedback, prion biology, and spatial quality control rather than as a dedicated metabolic enzyme or transporter. The studies use SSA2 in practical experimental contexts including purified chaperone biochemistry, isoform-swapping to map domain specificity, and reporter-based assays for misfolded-protein clearance and heat-shock regulation. (gaur2020theyeasthsp70 pages 13-14, gaur2020theyeasthsp70 pages 12-13, matveenko2025optimizationofconditions pages 1-3, garde2024feedbackcontrolof pages 4-7, rolli2024clearingthejunq pages 1-2)	Gaur et al., 2020, https://doi.org/10.1534/genetics.120.303190 (gaur2020theyeasthsp70 pages 13-14, gaur2020theyeasthsp70 pages 12-13); Matveenko et al., 2025, https://doi.org/10.17816/ecogen676918 (matveenko2025optimizationofconditions pages 1-3); Garde et al., 2024, https://doi.org/10.1101/2024.01.09.574867 (garde2024feedbackcontrolof pages 4-7); Rolli et al., 2024, https://doi.org/10.3389/fmolb.2024.1427542 (rolli2024clearingthejunq pages 1-2)

Table: This table summarizes identity, activity, localization, pathways, recent findings, quantitative data, and practical research uses for yeast SSA2 (UniProt P10592/YLL024C) using only the provided evidence contexts. It is useful as a compact evidence map for functional annotation and literature-backed reporting.

10) Limitations of this report (scope of retrieved evidence)

Although the user requested prioritization of 2023–2024 sources, the retrieved corpus contains SSA2-focused mechanistic details mostly in 2020 and 2024 sources, with no additional 2023 peer-reviewed SSA2-specific primary paper content beyond what was captured by the available texts. Database-level details (e.g., UniProt catalytic residue annotations, comprehensive interaction networks) were not directly retrieved via tools in this run; therefore, statements here are restricted to tool-retrieved primary/review evidence.

References

(gaur2020theyeasthsp70 pages 2-3): Deepika Gaur, Prashant Singh, Jyoti Guleria, Arpit Gupta, Satinderdeep Kaur, and Deepak Sharma. The yeast hsp70 cochaperone ydj1 regulates functional distinction of ssa hsp70s in the hsp90 chaperoning pathway. Genetics, 215:683-698, Jul 2020. URL: https://doi.org/10.1534/genetics.120.303190, doi:10.1534/genetics.120.303190. This article has 25 citations and is from a domain leading peer-reviewed journal.
(gaur2020theyeasthsp70 pages 1-1): Deepika Gaur, Prashant Singh, Jyoti Guleria, Arpit Gupta, Satinderdeep Kaur, and Deepak Sharma. The yeast hsp70 cochaperone ydj1 regulates functional distinction of ssa hsp70s in the hsp90 chaperoning pathway. Genetics, 215:683-698, Jul 2020. URL: https://doi.org/10.1534/genetics.120.303190, doi:10.1534/genetics.120.303190. This article has 25 citations and is from a domain leading peer-reviewed journal.
(gaur2020theyeasthsp70 pages 1-2): Deepika Gaur, Prashant Singh, Jyoti Guleria, Arpit Gupta, Satinderdeep Kaur, and Deepak Sharma. The yeast hsp70 cochaperone ydj1 regulates functional distinction of ssa hsp70s in the hsp90 chaperoning pathway. Genetics, 215:683-698, Jul 2020. URL: https://doi.org/10.1534/genetics.120.303190, doi:10.1534/genetics.120.303190. This article has 25 citations and is from a domain leading peer-reviewed journal.
(gaur2020theyeasthsp70 pages 9-9): Deepika Gaur, Prashant Singh, Jyoti Guleria, Arpit Gupta, Satinderdeep Kaur, and Deepak Sharma. The yeast hsp70 cochaperone ydj1 regulates functional distinction of ssa hsp70s in the hsp90 chaperoning pathway. Genetics, 215:683-698, Jul 2020. URL: https://doi.org/10.1534/genetics.120.303190, doi:10.1534/genetics.120.303190. This article has 25 citations and is from a domain leading peer-reviewed journal.
(matveenko2025optimizationofconditions pages 1-3): A. Matveenko, A. A. Tsvetkov, Tatiana M Rogoza, Yury A. Barbitoff, and G. Zhouravleva. Optimization of conditions for the productionof hsp70 chaperones in saccharomyces cerevisiae cells. Ecological genetics, Jun 2025. URL: https://doi.org/10.17816/ecogen676918, doi:10.17816/ecogen676918. This article has 0 citations.
(gaur2020theyeasthsp70 pages 12-13): Deepika Gaur, Prashant Singh, Jyoti Guleria, Arpit Gupta, Satinderdeep Kaur, and Deepak Sharma. The yeast hsp70 cochaperone ydj1 regulates functional distinction of ssa hsp70s in the hsp90 chaperoning pathway. Genetics, 215:683-698, Jul 2020. URL: https://doi.org/10.1534/genetics.120.303190, doi:10.1534/genetics.120.303190. This article has 25 citations and is from a domain leading peer-reviewed journal.
(gaur2020theyeasthsp70 pages 13-14): Deepika Gaur, Prashant Singh, Jyoti Guleria, Arpit Gupta, Satinderdeep Kaur, and Deepak Sharma. The yeast hsp70 cochaperone ydj1 regulates functional distinction of ssa hsp70s in the hsp90 chaperoning pathway. Genetics, 215:683-698, Jul 2020. URL: https://doi.org/10.1534/genetics.120.303190, doi:10.1534/genetics.120.303190. This article has 25 citations and is from a domain leading peer-reviewed journal.
(matveenko2025optimizationofconditions pages 7-9): A. Matveenko, A. A. Tsvetkov, Tatiana M Rogoza, Yury A. Barbitoff, and G. Zhouravleva. Optimization of conditions for the productionof hsp70 chaperones in saccharomyces cerevisiae cells. Ecological genetics, Jun 2025. URL: https://doi.org/10.17816/ecogen676918, doi:10.17816/ecogen676918. This article has 0 citations.
(rolli2024clearingthejunq pages 1-2): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(rolli2024clearingthejunq pages 12-13): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(garde2024feedbackcontrolof pages 4-7): Rania Garde, Annisa Dea, Madeline F. Herwig, and David Pincus. Feedback control of the heat shock response by spatiotemporal regulation of hsp70. bioRxiv, Jan 2024. URL: https://doi.org/10.1101/2024.01.09.574867, doi:10.1101/2024.01.09.574867. This article has 17 citations.
(rolli2024clearingthejunq pages 5-7): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(rolli2024clearingthejunq pages 7-9): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(rolli2024clearingthejunq media fa7c60b5): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(rolli2024clearingthejunq media b834e7ef): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(rolli2024clearingthejunq media 33462aaf): Sarah Rolli, Chloe A. Langridge, and Emily M. Sontag. Clearing the junq: the molecular machinery for sequestration, localization, and degradation of the junq compartment. Frontiers in Molecular Biosciences, Aug 2024. URL: https://doi.org/10.3389/fmolb.2024.1427542, doi:10.3389/fmolb.2024.1427542. This article has 8 citations.
(matveenko2025optimizationofconditions pages 9-10): A. Matveenko, A. A. Tsvetkov, Tatiana M Rogoza, Yury A. Barbitoff, and G. Zhouravleva. Optimization of conditions for the productionof hsp70 chaperones in saccharomyces cerevisiae cells. Ecological genetics, Jun 2025. URL: https://doi.org/10.17816/ecogen676918, doi:10.17816/ecogen676918. This article has 0 citations.

Artifacts

Edison artifact artifact-00

Citations

matveenko2025optimizationofconditions pages 7-9
garde2024feedbackcontrolof pages 4-7
matveenko2025optimizationofconditions pages 1-3
rolli2024clearingthejunq pages 1-2
rolli2024clearingthejunq pages 12-13
rolli2024clearingthejunq pages 5-7
rolli2024clearingthejunq pages 7-9
matveenko2025optimizationofconditions pages 9-10
https://doi.org/10.1101/2024.01.09.574867
https://doi.org/10.3389/fmolb.2024.1427542
https://doi.org/10.17816/ecogen676918
https://doi.org/10.1534/genetics.120.303190
https://doi.org/10.1534/genetics.120.303190,
https://doi.org/10.17816/ecogen676918,
https://doi.org/10.3389/fmolb.2024.1427542,
https://doi.org/10.1101/2024.01.09.574867,

📄 View Raw YAML

id: P10592
gene_symbol: SSA2
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:559292
  label: Saccharomyces cerevisiae
description: >-
  SSA2 encodes a constitutively expressed cytoplasmic Hsp70 chaperone in S. cerevisiae,
  highly homologous to SSA1 (97% amino acid identity). SSA2 is one of four SSA family
  members (SSA1-4) and is the most abundant, with approximately 364,000 molecules/cell
  (PMID:14562106), even more than SSA1. SSA2 functions as an ATP-dependent molecular
  chaperone that assists protein folding and refolding, interacts with Hsp90 and J-domain
  co-chaperones, participates in ubiquitin-dependent protein degradation, tRNA nuclear
  import, and is part of the HAP1 transcriptional repressor complex. SSA2 also binds
  human histatin 5 (HTN3) and mediates its fungicidal activity (PMID:12761219). SSA2 is
  found in the cytoplasm, cytosol, nucleus, plasma membrane, cell wall, vacuole membrane,
  mitochondria, and extracellular vesicles.
existing_annotations:
# ============================================================
# IBA ANNOTATIONS (phylogenetically inferred)
# ============================================================
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 nuclear localization is supported by NAS evidence from PMID:15102838 (HAP1
      repressor complex). As a close paralog of SSA1 (97% identity), SSA2 is expected to
      share nuclear localization. SSA1 has direct IDA evidence for nuclear localization
      (PMID:10347213).
    action: ACCEPT
    reason: >-
      Phylogenetically consistent. SSA2 is part of the HAP1 repressor complex in the
      nucleus (ComplexPortal CPX-1883). As a near-identical paralog of SSA1, nuclear
      localization is well-supported.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 is a major cytoplasmic Hsp70. IBA is consistent with IDA evidence from
      PMID:8755907 and UniProt subcellular location annotation.
    action: ACCEPT
    reason: >-
      Core localization. SSA2 is constitutively expressed and highly abundant in the
      cytoplasm.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 has been detected at the plasma membrane by HDA (PMID:16622836). IBA is
      consistent.
    action: ACCEPT
    reason: >-
      Supported by proteomics data. SSA2, like SSA1, is associated with the plasma
      membrane.
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 has ATPase activity supported by ISS evidence from PMID:8151709. As a 97%
      identical paralog of SSA1, which has well-characterized ATPase activity (PMID:7737974),
      SSA2's ATPase activity is certain.
    action: ACCEPT
    reason: >-
      Core molecular function. The ATPase activity drives the chaperone cycle. SSA2 is
      97% identical to SSA1 whose ATPase activity is biochemically established.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          The **N-terminal nucleotide-binding domain (NBD)** is implicated in ATPase-cycle control (Ydj1 binds the NBD to stimulate ATPase activity).
- term:
    id: GO:0031072
    label: heat shock protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 interacts with numerous heat shock proteins including HSP82, HSC82, SSE1,
      SIS1, STI1, SBA1, and HSP26/HSP42. UniProt lists extensive IntAct interaction data.
    action: ACCEPT
    reason: >-
      Well-supported by extensive IPI data. SSA2 physically interacts with HSP82 (4
      experiments), HSC82 (3 experiments), SSE1 (4 experiments), SIS1 (5 experiments),
      STI1 (4 experiments), and other chaperones.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          **Hsp90 (Hsp82)**: receives certain clients after Hsp70 processing; Ssa2 participates in upstream client handling and transfer toward Hsp90.
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          **Hsp40/J-domain cochaperone Ydj1**: recruits misfolded clients to Hsp70 and stimulates Hsp70 ATPase activity and substrate transfer.
- term:
    id: GO:0044183
    label: protein folding chaperone
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 is a bona fide protein folding chaperone. PMID:8947547 demonstrated that
      immunodepletion of Ssa1/2p from yeast cytosol dramatically reduced refolding of
      denatured luciferase. PMID:9789005 showed SSA-dependent folding of newly translated
      OTC in vivo.
    action: ACCEPT
    reason: >-
      Core molecular function. SSA2 is an ATP-dependent protein folding chaperone,
      functionally interchangeable with SSA1 for refolding activity.
    supported_by:
      - reference_id: PMID:8947547
        supporting_text: "Depletion of Ssa1/2p had no effect on the ability of the yeast lysate to synthesize enzymatically active luciferase, but had a dramatic effect on the ability of the lysate to refold chemically denatured luciferase."
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          **SSA2 encodes an ATP-dependent molecular chaperone of the Hsp70 family.** Rather than catalyzing a metabolic reaction with a defined substrate/product, Ssa2 performs **ATP-driven cycles of client binding and release** to prevent aggregation and promote folding/refolding and quality control.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 is primarily a cytosolic protein. IBA is consistent with IDA evidence from
      PMID:16806052.
    action: ACCEPT
    reason: >-
      Core localization. SSA2 is the major cytosolic Hsp70 along with SSA1.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          Fluorescence microscopy of N-terminally tagged Ssa proteins (including **Ssa2**) shows predominantly **diffuse** signal in most cells, supporting predominant **cytosolic localization** under those conditions.
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          Gaur et al. explicitly treat Ssa2 as one of four **cytosolic** Ssa Hsp70s acting in the Hsp90 pathway.
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SSA2 is directly involved in protein refolding. PMID:8947547 demonstrated that
      Ssa1/2p depletion dramatically reduced refolding capacity of yeast cytosol.
    action: ACCEPT
    reason: >-
      Well-supported core function. Refolding of denatured proteins is a central activity
      of SSA2 as demonstrated by PMID:8947547.
    supported_by:
      - reference_id: PMID:8947547
        supporting_text: "These results demonstrate, for the first time, the refolding activity of Ssa1/2p in the context of the yeast cytosol, and define refolding activity as a chaperone function specific to Ssa1/2p"
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          Ydj1-assisted luciferase refolding activity was reported as **~25–30-fold higher with Ssa2 than with Ssa4**, consistent with stronger Ydj1–Ssa2 functional coupling.
# ============================================================
# IEA ANNOTATIONS (computationally inferred)
# ============================================================
- term:
    id: GO:0000049
    label: tRNA binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      IEA annotation for tRNA binding. Consistent with IDA evidence from PMID:25853343
      which demonstrated that SSA2 directly binds tRNA as part of a tRNA nuclear import
      system.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct but non-core. Supported by direct experimental evidence (IDA from
      PMID:25853343). tRNA binding is a specialized moonlighting activity of SSA2.
- term:
    id: GO:0000166
    label: nucleotide binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      SSA2 binds ATP and ADP as part of its chaperone cycle. This is a parent term of ATP
      binding and is correct but overly general.
    action: ACCEPT
    reason: >-
      Correct but general. More specific terms (ATP binding, ATP hydrolysis activity) are
      also annotated, so this broader IEA is acceptable as a redundant parent.
- term:
    id: GO:0000329
    label: fungal-type vacuole membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 localization to the vacuole membrane is supported by IDA evidence from
      PMID:10745074, which showed cytosolic Hsp70 involvement in aminopeptidase I
      transport to the vacuole.
    action: ACCEPT
    reason: >-
      Correct. Consistent with direct experimental evidence (IDA from PMID:10745074).
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      SSA2 binds ATP through its nucleotide-binding domain. This is core to its function.
      Also supported by IDA from PMID:10893257.
    action: ACCEPT
    reason: >-
      Correct and fundamental. ATP binding is essential for the SSA2 chaperone cycle.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          This is evidenced in (i) biochemical handling consistent with ATP-binding Hsp70 behavior (purification via ATP-agarose and ATP elution) and (ii) mechanistic descriptions of cochaperone control of the Hsp70 ATPase cycle (Ydj1 stimulating ATPase activity and substrate transfer).
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Duplicate of the IBA and IDA annotations for cytoplasm. Correct.
    action: ACCEPT
    reason: >-
      Correct. Redundant with IBA and IDA annotations but acceptable.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 is directly involved in protein folding as demonstrated experimentally
      (IDA from PMID:7867784, IMP from PMID:9448096). IEA is consistent.
    action: ACCEPT
    reason: >-
      Correct. Consistent with direct experimental evidence.
- term:
    id: GO:0006616
    label: SRP-dependent cotranslational protein targeting to membrane, translocation
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 has been implicated in protein translocation to the ER membrane (IMP from
      PMID:8754838). However, PMID:8947547 found that depletion of Ssa1/2p had no effect
      on translocation efficiency in vitro. The role may be more indirect.
    action: KEEP_AS_NON_CORE
    reason: >-
      Consistent with the existing IMP annotation from PMID:8754838, but this is not a
      core function. PMID:8947547 showed depletion had no effect on translocation
      efficiency in vitro, suggesting an indirect role.
    supported_by:
      - reference_id: PMID:8947547
        supporting_text: "Depletion of Ssa1/2p had no effect on the efficiency of translocation in this in vitro assay."
- term:
    id: GO:0009277
    label: fungal-type cell wall
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 has been detected in the cell wall by IDA (PMID:8755907). IEA is consistent.
      UniProt also annotates SSA2 to the cell wall.
    action: ACCEPT
    reason: >-
      Correct. Consistent with direct experimental evidence and UniProt annotation.
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      Duplicate of IBA and ISS annotations. Correct InterPro-based annotation.
    action: ACCEPT
    reason: >-
      Correct. Redundant with IBA and ISS annotations but acceptable.
- term:
    id: GO:0033554
    label: cellular response to stress
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 is a heat shock protein involved in stress response. Although SSA2 is
      constitutively expressed (unlike the stress-induced SSA3/SSA4), it participates in
      protein quality control during stress.
    action: ACCEPT
    reason: >-
      Correct but general. SSA2 responds to and helps manage various stresses through its
      chaperone activity.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          Disrupting the Hsf1-binding site in SSA2 (**ssa2ΔHSE**) was associated with **elevated basal HSE-YFP reporter** and **reduced induction after prolonged heat shock**, and the authors interpret the reduced induction as explained by the increased basal reporter level—consistent with SSA2 contributing to basal repression/feedback behavior in the Hsf1 regulon context.
- term:
    id: GO:0043161
    label: proteasome-mediated ubiquitin-dependent protein catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 participates in ubiquitin-dependent protein degradation. Consistent with IGI
      evidence from PMID:27178214.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct but non-core. SSA2 assists in presenting misfolded substrates to the
      ubiquitin-proteasome system as part of its broader protein quality control role.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          SSA2 is an **ATP-dependent molecular chaperone** of the Hsp70 family that binds ATP and acts with **Hsp40 cochaperones** and **nucleotide exchange factors** to prevent aggregation, assist folding/refolding, and support degradation/translocation of client proteins.
- 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 considered for obsoletion. SSA2 does
      bind unfolded proteins, but this is part of its chaperone activity, not a standalone
      binding function. The appropriate replacement is GO:0140662 (ATP-dependent protein
      folding chaperone).
    action: MODIFY
    reason: >-
      GO:0051082 is targeted for obsoletion. SSA2 binds unfolded proteins as part of its
      ATP-dependent chaperone cycle. The correct annotation is GO:0140662 (ATP-dependent
      protein folding chaperone) or the already-present GO:0044183 (protein folding
      chaperone).
    proposed_replacement_terms:
      - id: GO:0140662
        label: ATP-dependent protein folding chaperone
- term:
    id: GO:0051170
    label: import into nucleus
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      SSA2 is involved in tRNA import into the nucleus (IMP from PMID:25853343,
      PMID:33074312). This IEA is a broader parent term consistent with the experimental
      evidence.
    action: ACCEPT
    reason: >-
      Correct but general. Consistent with the more specific experimental annotation for
      tRNA import into nucleus.
# ============================================================
# PROTEIN BINDING IPI ANNOTATIONS
# ============================================================
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:14729968
  review:
    summary: >-
      IPI evidence from ctf13-30/CTF13 haploinsufficiency screen. SSA2 is a chaperone
      that binds many client proteins.
    action: MODIFY
    reason: >-
      Protein binding is uninformative for a chaperone that by definition binds many
      proteins. Better captured by GO:0044183 (protein folding chaperone).
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:15766533
  review:
    summary: >-
      IPI evidence for SSA2 binding HSP82 and HSC82 from chaperone network mapping.
      These are well-known Hsp70-Hsp90 interactions.
    action: MODIFY
    reason: >-
      Protein binding is uninformative. The Hsp70-Hsp90 interaction is better captured
      by GO:0031072 (heat shock protein binding) which is already annotated via IBA.
    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:16284124
  review:
    summary: >-
      IPI evidence for SSA2 binding proteasome subunits from a proteasome interactome
      study.
    action: MODIFY
    reason: >-
      Protein binding is uninformative. The SSA2-proteasome interaction relates to its
      role in ubiquitin-dependent protein degradation.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16429126
  review:
    summary: >-
      Large-scale proteome survey (Gavin et al. 2006) identifying many SSA2 interaction
      partners by TAP-MS.
    action: MODIFY
    reason: >-
      Protein binding is uninformative for a chaperone. The interactions represent
      chaperone-client and chaperone-cochaperone relationships.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16606443
  review:
    summary: >-
      IPI evidence from analysis of WW domain-containing proteins and their interacting
      partners.
    action: MODIFY
    reason: >-
      Protein binding is uninformative for a chaperone.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17441508
  review:
    summary: >-
      IPI evidence for SSA2 binding SGT2 via Ydj1 co-chaperone.
    action: MODIFY
    reason: >-
      Protein binding is uninformative. The interaction with SGT2/Ydj1 relates to SSA2's
      chaperone function.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17892321
  review:
    summary: >-
      Structure-templated predictions of protein interactions.
    action: MODIFY
    reason: >-
      Protein binding is uninformative for a chaperone.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19536198
  review:
    summary: >-
      Atlas of chaperone-protein interactions (Gong et al. 2009). Systematic mapping of
      SSA2 chaperone-client interactions.
    action: MODIFY
    reason: >-
      Protein binding is uninformative. These interactions represent chaperone-client
      relationships inherent to SSA2's chaperone function.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:37070168
  review:
    summary: >-
      RNA-dependent interactome study.
    action: MODIFY
    reason: >-
      Protein binding is uninformative for a chaperone.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:37968396
  review:
    summary: >-
      Social and structural architecture of yeast protein interactome. Large-scale study.
    action: MODIFY
    reason: >-
      Protein binding is uninformative for a chaperone.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:9819422
  review:
    summary: >-
      IPI evidence for SSA2 binding HSP82 and CPR7 via Cns1.
    action: MODIFY
    reason: >-
      Protein binding is uninformative. The Ssa2-Hsp82/Cpr7 interaction is a chaperone
      network interaction better captured by GO:0031072.
    proposed_replacement_terms:
      - id: GO:0031072
        label: heat shock protein binding
# ============================================================
# NAS ANNOTATIONS
# ============================================================
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: NAS
  original_reference_id: PMID:15102838
  review:
    summary: >-
      NAS annotation from ComplexPortal for SSA2 nuclear localization in context of the
      HAP1 repressor complex (CPX-1883). Consistent with IBA.
    action: ACCEPT
    reason: >-
      Correct. SSA2 is present in the nucleus as part of the HAP1 repressor complex.
- term:
    id: GO:0045892
    label: negative regulation of DNA-templated transcription
  evidence_type: NAS
  original_reference_id: PMID:15102838
  review:
    summary: >-
      SSA2 is part of the HAP1 transcriptional repressor complex (ComplexPortal CPX-1883)
      where it represses HAP1-dependent transcription in the absence of heme.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but secondary function. SSA2 acts as a repressive chaperone holdase for
      HAP1, preventing transcriptional activation. This is not a core molecular function
      but rather a consequence of its chaperone activity on a specific client.
- term:
    id: GO:0070482
    label: response to oxygen levels
  evidence_type: NAS
  original_reference_id: PMID:15102838
  review:
    summary: >-
      SSA2 is part of the HAP1 complex that responds to heme/oxygen levels.
    action: KEEP_AS_NON_CORE
    reason: >-
      Secondary consequence of SSA2's role in the HAP1 repressor complex, not a core
      function.
- term:
    id: GO:0070482
    label: response to oxygen levels
  evidence_type: NAS
  original_reference_id: PMID:9632766
  review:
    summary: >-
      Same process annotation from a different reference. PMID:9632766 describes the
      higher-order HAP1 complex mechanism.
    action: KEEP_AS_NON_CORE
    reason: >-
      Duplicate process annotation for the same indirect role. SSA2 participates in
      oxygen/heme signaling through the HAP1 complex but this is not its core function.
# ============================================================
# IDA/IMP/IGI/ISS/HDA ANNOTATIONS (experimental evidence)
# ============================================================
- term:
    id: GO:1903561
    label: extracellular vesicle
  evidence_type: IDA
  original_reference_id: PMID:38711329
  review:
    summary: >-
      PMID:38711329 detected SSA2 in extracellular vesicles during thermotolerance
      studies.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but peripheral localization. SSA2 in extracellular vesicles likely reflects
      its abundance rather than a specific targeting function.
- term:
    id: GO:0009267
    label: cellular response to starvation
  evidence_type: IMP
  original_reference_id: PMID:25853343
  review:
    summary: >-
      PMID:25853343 showed SSA2 involvement in tRNA nuclear import which is regulated by
      nutrient status/starvation.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but secondary function. The starvation response of SSA2 is related to its
      role in tRNA import regulation.
- term:
    id: GO:0035719
    label: tRNA import into nucleus
  evidence_type: IMP
  original_reference_id: PMID:33074312
  review:
    summary: >-
      PMID:33074312 demonstrated SSA2's role in tRNA nuclear import via mutant phenotype
      analysis.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but specialized function. tRNA nuclear import is a moonlighting activity
      of SSA2 distinct from its core chaperone function.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HDA
  original_reference_id: PMID:24769239
  review:
    summary: >-
      HDA evidence from mitochondrial proteome/phosphoproteome study. SSA2 was detected
      in mitochondrial fractions.
    action: ACCEPT
    reason: >-
      Correct. SSA2 associates with mitochondria, consistent with IDA from PMID:16806052
      and its role in protein translocation across mitochondrial membranes.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: HDA
  original_reference_id: PMID:16622836
  review:
    summary: >-
      HDA evidence from plasma membrane proteome study. SSA2 was detected in the plasma
      membrane fraction.
    action: ACCEPT
    reason: >-
      Correct. SSA2 is associated with the plasma membrane, consistent with IBA.
- term:
    id: GO:0043161
    label: proteasome-mediated ubiquitin-dependent protein catabolic process
  evidence_type: IGI
  original_reference_id: PMID:27178214
  review:
    summary: >-
      PMID:27178214 demonstrated SSA family requirement for ubiquitin-dependent
      degradation of short-lived and abnormal proteins via genetic interaction.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but secondary function. SSA2 assists in presenting misfolded substrates to
      the ubiquitin-proteasome system as part of its broader protein quality control role.
- term:
    id: GO:0000049
    label: tRNA binding
  evidence_type: IDA
  original_reference_id: PMID:25853343
  review:
    summary: >-
      PMID:25853343 demonstrated that cytosolic Hsp70 (SSA2) directly binds tRNA as part
      of a tRNA nuclear import system.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but specialized function. tRNA binding is a moonlighting activity of SSA2
      related to its role in tRNA nuclear import.
- term:
    id: GO:0035719
    label: tRNA import into nucleus
  evidence_type: IMP
  original_reference_id: PMID:25853343
  review:
    summary: >-
      PMID:25853343 demonstrated SSA2's role in tRNA import into the nucleus.
    action: KEEP_AS_NON_CORE
    reason: >-
      Genuine but specialized function. Same as the other tRNA import annotation, from
      a different PMID.
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: ISS
  original_reference_id: PMID:8151709
  review:
    summary: >-
      ISS annotation based on molecular evolution of the HSP70 multigene family.
      Consistent with SSA2's function as an ATPase.
    action: ACCEPT
    reason: >-
      Correct. SSA2 has ATPase activity essential for its chaperone cycle. Redundant with
      IBA but acceptable.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: ISS
  original_reference_id: PMID:8151709
  review:
    summary: >-
      GO:0051082 is targeted for obsoletion. SSA2 binds unfolded proteins as part of its
      ATP-dependent chaperone cycle, not as a standalone binding activity.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. The correct replacement is GO:0140662 (ATP-dependent
      protein folding chaperone). SSA2 binds unfolded proteins as part of its chaperone
      function.
    proposed_replacement_terms:
      - id: GO:0140662
        label: ATP-dependent protein folding chaperone
- term:
    id: GO:0000329
    label: fungal-type vacuole membrane
  evidence_type: IDA
  original_reference_id: PMID:10745074
  review:
    summary: >-
      PMID:10745074 showed cytosolic Hsp70s are involved in transport of aminopeptidase I
      from cytoplasm into the vacuole, and SSA2 localizes to the vacuole membrane.
    action: ACCEPT
    reason: >-
      Correct localization supported by direct experimental evidence.
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IDA
  original_reference_id: PMID:10893257
  review:
    summary: >-
      PMID:10893257 demonstrated that SSA2 binds ATP, and this binding is required for
      import of fructose-1,6-bisphosphatase into Vid vesicles.
    action: ACCEPT
    reason: >-
      Core molecular function with direct experimental evidence.
    supported_by:
      - reference_id: PMID:10893257
        supporting_text: "The heat shock protein Ssa2p was identified as one of the ATP binding proteins involved in FBPase import."
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:8755907
  review:
    summary: >-
      PMID:8755907 identified Hsp70 family members including SSA2 in the cell wall and
      confirmed cytoplasmic localization.
    action: ACCEPT
    reason: >-
      Correct core localization with direct experimental evidence.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: PMID:16806052
  review:
    summary: >-
      PMID:16806052 detected SSA2 in mitochondrial fractions. SSA2 likely associates with
      mitochondria in the context of protein import.
    action: ACCEPT
    reason: >-
      Correct. SSA2 associates with mitochondria, consistent with HDA from PMID:24769239
      and its role in maintaining precursors in import-competent conformations.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: PMID:16806052
  review:
    summary: >-
      PMID:16806052 confirmed SSA2 cytosolic localization.
    action: ACCEPT
    reason: >-
      Correct core localization. SSA2 is predominantly cytosolic.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IDA
  original_reference_id: PMID:7867784
  review:
    summary: >-
      Direct assay demonstrating SSA2 involvement in protein folding.
    action: ACCEPT
    reason: >-
      Core biological process. Direct experimental demonstration of SSA2's role in protein
      folding.
    supported_by:
      - reference_id: file:yeast/SSA2/SSA2-deep-research-falcon.md
        reference_section_type: OTHER
        supporting_text: |-
          Using v-Src as an Hsp90 client, Gaur et al. show that the Hsp40 cochaperone **Ydj1 binds misfolded client, recruits it to Hsp70, and transfers it preferentially to Ssa2** (relative to Ssa4). Transfer to Ssa2 supports subsequent engagement with Hsp90 and client maturation.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IMP
  original_reference_id: PMID:9448096
  review:
    summary: >-
      PMID:9448096 showed that ssa1ssa2 mutants had significantly lower luciferase
      activity than wild type, demonstrating SSA proteins are needed for folding of
      proteins. The reduced folding capacity in ssa1ssa2 cells closely correlated with
      the amount of Ssa proteins present.
    action: ACCEPT
    reason: >-
      Core biological process. Mutant phenotype demonstrates SSA2 (with SSA1) is required
      for protein folding in vivo.
    supported_by:
      - reference_id: PMID:9448096
        supporting_text: "The luciferase activity was significantly lower in ssa1ssa2 transformants than in the wild type (wt) cell transformed with the same plasmid"
      - reference_id: PMID:9448096
        supporting_text: "It is suggested that constitutional Ssa \"chaperones\" are needed for the folding of proteins and, in cells lacking Ssa1 and Ssa2, the increased Ssa4 is thought to partly compensate for their role in the folding of luciferase in vivo"
- term:
    id: GO:0006616
    label: SRP-dependent cotranslational protein targeting to membrane, translocation
  evidence_type: IMP
  original_reference_id: PMID:8754838
  review:
    summary: >-
      PMID:8754838 showed that SSA-deficient mutants (ssa1ts ssa2 ssa3 ssa4) had
      translocation defects for prepro-alpha-factor and proteinase A. However,
      PMID:8947547 later showed depletion of Ssa1/2p had no effect on translocation
      efficiency in vitro.
    action: KEEP_AS_NON_CORE
    reason: >-
      The direct role in SRP-dependent translocation is debated. PMID:8947547 showed
      depletion did not affect translocation efficiency. The in vivo phenotype from
      PMID:8754838 may reflect SSA2's general chaperone function keeping precursors
      translocation-competent.
    supported_by:
      - reference_id: PMID:8754838
        supporting_text: "Of six proteins destined for the endoplasmic reticulum, the translocation of only prepro-alpha-factor and proteinase A was inhibited."
      - reference_id: PMID:8947547
        supporting_text: "Depletion of Ssa1/2p had no effect on the efficiency of translocation in this in vitro assay."
- term:
    id: GO:0009277
    label: fungal-type cell wall
  evidence_type: IDA
  original_reference_id: PMID:8755907
  review:
    summary: >-
      PMID:8755907 directly identified SSA2 as a cell wall protein. UniProt also
      annotates SSA2 subcellular location as "Secreted, cell wall."
    action: ACCEPT
    reason: >-
      Correct localization. SSA2 is present in the cell wall.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IGI
  original_reference_id: PMID:9789005
  review:
    summary: >-
      PMID:9789005 showed that the SSA class of Hsp70 proteins assists folding of newly
      translated OTC in vivo. The IGI evidence comes from genetic interaction among SSA
      family members. GO:0051082 is targeted for obsoletion.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. PMID:9789005 actually demonstrates chaperone
      activity, not mere binding. The correct replacement is GO:0140662 (ATP-dependent
      protein folding chaperone).
    proposed_replacement_terms:
      - id: GO:0140662
        label: ATP-dependent protein folding chaperone
    supported_by:
      - reference_id: PMID:9789005
        supporting_text: "yeast cytosolic OTC is assisted to its native state by the SSA class of yeast cytosolic Hsp70 proteins"
# ============================================================
# NEW ANNOTATIONS (suggested additions)
# ============================================================
- term:
    id: GO:0140662
    label: ATP-dependent protein folding chaperone
  evidence_type: IDA
  original_reference_id: PMID:8947547
  review:
    summary: >-
      SSA2 is an ATP-dependent protein folding chaperone. PMID:8947547 demonstrated that
      Ssa1/2p depletion dramatically reduced refolding of denatured luciferase in yeast
      cytosol, and PMID:9789005 showed SSA-dependent folding of newly translated OTC.
      GO:0140662 is the most specific and accurate MF term, replacing the obsoleting
      GO:0051082. UniProt already assigns this via InterPro (IEA).
    action: NEW
    reason: >-
      GO:0140662 (ATP-dependent protein folding chaperone) is the most specific and
      accurate molecular function term for SSA2. It replaces the obsoleting GO:0051082
      and is more specific than GO:0044183.
    additional_reference_ids:
      - PMID:9789005
      - PMID:9448096
    supported_by:
      - reference_id: PMID:8947547
        supporting_text: "These results demonstrate, for the first time, the refolding activity of Ssa1/2p in the context of the yeast cytosol"
      - reference_id: PMID:9789005
        supporting_text: "yeast cytosolic OTC is assisted to its native state by the SSA class of yeast cytosolic Hsp70 proteins"
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  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: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:7867784
  title: Cooperation of the molecular chaperone Ydj1 with specific Hsp70 homologs to
    suppress protein aggregation.
  findings:
    - statement: Ydj1 cooperated with Ssa Hsp70 proteins in the prevention of protein aggregation
      supporting_text: "Ydj1p cooperated with Ssa Hsp70 proteins in the prevention of protein aggregation, but not with the Ssb Hsp70 proteins."
- id: PMID:8151709
  title: Molecular evolution of the HSP70 multigene family.
  findings:
    - statement: ISS-based annotation of ATPase and unfolded protein binding for SSA2
      supporting_text: "The Saccharomyces cerevisiae HSP70 family is comprised of eight members"
- id: PMID:8754838
  title: Functional interaction of cytosolic hsp70 and a DnaJ-related protein, Ydj1p,
    in protein translocation in vivo.
  findings:
    - statement: SSA-deficient mutants show translocation defects for specific ER-targeted proteins
      supporting_text: "Of six proteins destined for the endoplasmic reticulum, the translocation of only prepro-alpha-factor and proteinase A was inhibited"
- id: PMID:8755907
  title: Members of the Hsp70 family of proteins in the cell wall of Saccharomyces cerevisiae.
  findings:
    - statement: Identified SSA2 in the cell wall and confirmed cytoplasmic localization
      supporting_text: "the heat shock protein 70 (Hsp70) products of these genes, previously thought to be restricted to the cell interior, are also present in the cell wall"
- id: PMID:8947547
  title: The refolding activity of the yeast heat shock proteins Ssa1 and Ssa2 defines
    their role in protein translocation.
  findings:
    - statement: Demonstrated Ssa1/2 refolding activity with denatured luciferase
    - statement: Found Ssa1/2 depletion does not affect translocation in vitro
- id: PMID:9448096
  title: Role of Hsp70 subfamily, Ssa, in protein folding in yeast cells, seen in
    luciferase-transformed ssa mutants.
  findings:
    - statement: Demonstrated SSA proteins are needed for protein folding in vivo
- id: PMID:9632766
  title: 'Molecular mechanism governing heme signaling in yeast: a higher-order complex
    mediates heme regulation of the transcriptional activator HAP1.'
  findings:
    - statement: Described the HAP1 higher-order complex mechanism with Hsp70
- id: PMID:9789005
  title: Folding in vivo of a newly translated yeast cytosolic enzyme is mediated by
    the SSA class of cytosolic yeast Hsp70 proteins.
  findings:
    - statement: SSA class Hsp70s assist de novo folding of newly translated cytosolic enzymes
- id: PMID:9819422
  title: Cns1 is an essential protein associated with the hsp90 chaperone complex in
    Saccharomyces cerevisiae that can restore cyclophilin 40-dependent functions in
    cpr7Delta cells.
  findings:
    - statement: SSA2 associates with the Hsp90 chaperone complex via Cns1/Cpr7
- id: PMID:10745074
  title: Cytosolic Hsp70s are involved in the transport of aminopeptidase 1 from the
    cytoplasm into the vacuole.
  findings:
    - statement: SSA2 involved in Ape1 transport to vacuole and localizes to vacuole membrane
- id: PMID:10893257
  title: The heat shock protein Ssa2p is required for import of fructose-1,6-bisphosphatase
    into Vid vesicles.
  findings:
    - statement: SSA2 binds ATP and is required for FBPase import into Vid vesicles
- id: PMID:14562106
  title: Global analysis of protein expression in yeast.
  findings:
    - statement: SSA2 present at 364,000 molecules/cell in log phase
- id: PMID:14729968
  title: The ctf13-30/CTF13 genomic haploinsufficiency modifier screen identifies the
    yeast chromatin remodeling complex RSC, which is required for the establishment of
    sister chromatid cohesion.
  findings: []
- id: PMID:15102838
  title: 'A novel mode of chaperone action: heme activation of Hap1 by enhanced association
    of Hsp90 with the repressed Hsp70-Hap1 complex.'
  findings:
    - statement: SSA2 is part of the HAP1 repressor complex (CPX-1883)
- id: PMID:15766533
  title: 'Navigating the chaperone network: an integrative map of physical and genetic
    interactions mediated by the hsp90 chaperone.'
  findings:
    - statement: Mapped SSA2 interactions with Hsp90 chaperone network
- id: PMID:16284124
  title: 'An integrated mass spectrometry-based proteomic approach: quantitative analysis
    of tandem affinity-purified in vivo cross-linked protein complexes (QTAX) to decipher
    the 26 S proteasome-interacting network.'
  findings:
    - statement: SSA2 interacts with the 26S proteasome
- id: PMID:16429126
  title: Proteome survey reveals modularity of the yeast cell machinery.
  findings:
    - statement: Large-scale TAP-MS identifying numerous SSA2 interactors
- id: PMID:16606443
  title: Comparative analysis of Saccharomyces cerevisiae WW domains and their interacting
    proteins.
  findings: []
- id: PMID:16622836
  title: The plasma membrane proteome of Saccharomyces cerevisiae and its response to
    the antifungal calcofluor.
  findings:
    - statement: SSA2 detected in the plasma membrane proteome
- id: PMID:16806052
  title: MMI1 (YKL056c, TMA19), the yeast orthologue of the translationally controlled
    tumor protein (TCTP) has apoptotic functions and interacts with both microtubules
    and mitochondria.
  findings:
    - statement: SSA2 detected in cytosol and mitochondrial fractions
- id: PMID:17441508
  title: SGT2 and MDY2 interact with molecular chaperone YDJ1 in Saccharomyces cerevisiae.
  findings:
    - statement: SSA2 interacts with SGT2 via Ydj1 co-chaperone
- id: PMID:17892321
  title: Structure-templated predictions of novel protein interactions from sequence
    information.
  findings: []
- id: PMID:19536198
  title: 'An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications
    to protein folding pathways in the cell.'
  findings:
    - statement: Systematic mapping of SSA2 chaperone-client interactions
- id: PMID:24769239
  title: Quantitative variations of the mitochondrial proteome and phosphoproteome during
    fermentative and respiratory growth in Saccharomyces cerevisiae.
  findings:
    - statement: SSA2 detected in mitochondrial fraction
- id: PMID:25853343
  title: Cytosolic Hsp70 and co-chaperones constitute a novel system for tRNA import
    into the nucleus.
  findings:
    - statement: SSA2 binds tRNA and facilitates its import into the nucleus
- id: PMID:27178214
  title: The requirements of yeast Hsp70 of SSA family for the ubiquitin-dependent degradation
    of short-lived and abnormal proteins.
  findings:
    - statement: SSA family required for ubiquitin-dependent degradation
- id: PMID:33074312
  title: A novel assay provides insight into tRNAPhe retrograde nuclear import and re-export
    in S. cerevisiae.
  findings:
    - statement: SSA2 role in tRNA nuclear import
      supporting_text: "the Hsp70 protein Ssa2 mediates import specifically in the latter"
- id: PMID:37070168
  title: RNA-dependent interactome allows network-based assignment of RNA-binding protein
    function.
  findings: []
- id: PMID:37968396
  title: The social and structural architecture of the yeast protein interactome.
  findings: []
- id: PMID:38711329
  title: Thermotolerance in S. cerevisiae as a model to study extracellular vesicle
    biology.
  findings:
    - statement: SSA2 detected in extracellular vesicles
- id: PMID:12761219
  title: Candida albicans Ssa1/2p is the cell envelope binding protein for human salivary
    histatin 5.
  findings:
    - statement: SSA2 binds human histatin 5 and mediates its fungicidal activity
- id: file:yeast/SSA2/SSA2-deep-research-falcon.md
  title: Falcon deep research report on SSA2 (Saccharomyces cerevisiae, UniProt P10592/YLL024C)
  findings:
    - statement: >-
        SSA2 (YLL024C) encodes Ssa2, a cytosolic Hsp70 (Stress-Seventy subfamily A)
        chaperone; it is one of four cytosolic Ssa isoforms (Ssa1-4), with Ssa1/Ssa2
        constitutively expressed and Ssa3/Ssa4 stress-inducible.
      reference_section_type: OTHER
      supporting_text: |-
        In the retrieved literature, SSA2 is consistently described as one of four cytosolic Ssa Hsp70 isoforms (Ssa1–4), with **Ssa1/Ssa2 constitutively expressed** and **Ssa3/Ssa4 stress-inducible**, matching the UniProt-provided identity and family assignment.
    - statement: >-
        SSA2 is an ATP-dependent molecular chaperone of the Hsp70 family that performs
        ATP-driven cycles of client binding and release to prevent aggregation and promote
        folding/refolding and quality control, rather than catalyzing a metabolic reaction.
      reference_section_type: OTHER
      supporting_text: |-
        **SSA2 encodes an ATP-dependent molecular chaperone of the Hsp70 family.** Rather than catalyzing a metabolic reaction with a defined substrate/product, Ssa2 performs **ATP-driven cycles of client binding and release** to prevent aggregation and promote folding/refolding and quality control.
    - statement: >-
        The N-terminal nucleotide-binding domain (NBD) mediates ATPase-cycle control (the
        Hsp40 cochaperone Ydj1 binds the NBD to stimulate ATPase activity), while the
        C-terminal region contributes to substrate transfer and isoform specificity.
      reference_section_type: OTHER
      supporting_text: |-
        The **N-terminal nucleotide-binding domain (NBD)** is implicated in ATPase-cycle control (Ydj1 binds the NBD to stimulate ATPase activity).
    - statement: >-
        SSA2 functions within the Hsp70-Hsp90 chaperone pathway; Ydj1 recruits misfolded
        clients to Hsp70 and transfers them preferentially to Ssa2 (over Ssa4), supporting
        subsequent Hsp90 engagement and client maturation.
      reference_section_type: OTHER
      supporting_text: |-
        Using v-Src as an Hsp90 client, Gaur et al. show that the Hsp40 cochaperone **Ydj1 binds misfolded client, recruits it to Hsp70, and transfers it preferentially to Ssa2** (relative to Ssa4). Transfer to Ssa2 supports subsequent engagement with Hsp90 and client maturation.
    - statement: >-
        Ssa isoforms are not fully redundant; Ydj1-assisted luciferase refolding was
        ~25-30-fold higher with Ssa2 than with Ssa4, reflecting stronger Ydj1-Ssa2
        functional coupling.
      reference_section_type: OTHER
      supporting_text: |-
        Ydj1-assisted luciferase refolding activity was reported as **~25–30-fold higher with Ssa2 than with Ssa4**, consistent with stronger Ydj1–Ssa2 functional coupling.
    - statement: >-
        Ssa2 is localized predominantly to the cytosol; tagged Ssa proteins including Ssa2
        show predominantly diffuse cytosolic distribution by fluorescence microscopy.
      reference_section_type: OTHER
      supporting_text: |-
        Fluorescence microscopy of N-terminally tagged Ssa proteins (including **Ssa2**) shows predominantly **diffuse** signal in most cells, supporting predominant **cytosolic localization** under those conditions.
    - statement: >-
        Ssa1/Ssa2 are required for formation/localization of the cytoplasmic JUNQ
        compartment adjacent to the nucleus-vacuole junction (NVJ) and for degradation of
        cytoplasmic misfolded proteins routed there; loss of both shifts handling toward
        peripheral IPOD-like inclusions and inhibits clearance of a misfolded reporter.
      reference_section_type: OTHER
      supporting_text: |-
        Ssa1/Ssa2 are required for formation/localization of the cytoplasmic **JUNQ** compartment adjacent to the **nucleus–vacuole junction (NVJ)** and for degradation of cytoplasmic misfolded proteins that are routed there.
    - statement: >-
        In a 2024 heat-shock-response feedback study, SSA2 had the highest expression rank
        among SSA paralogs (Ssa3 < Ssa4 < Ssa1 < Ssa2), and deleting its Hsf1-binding site
        (ssa2-deltaHSE) elevated basal HSE-YFP reporter and reduced heat-shock induction,
        consistent with SSA2 contributing to basal repression/feedback of the Hsf1 regulon.
      reference_section_type: OTHER
      supporting_text: |-
        Disrupting the Hsf1-binding site in SSA2 (**ssa2ΔHSE**) was associated with **elevated basal HSE-YFP reporter** and **reduced induction after prolonged heat shock**, and the authors interpret the reduced induction as explained by the increased basal reporter level—consistent with SSA2 contributing to basal repression/feedback behavior in the Hsf1 regulon context.
core_functions:
  - molecular_function:
      id: GO:0140662
      label: ATP-dependent protein folding chaperone
    directly_involved_in:
      - id: GO:0006457
        label: protein folding
      - id: GO:0042026
        label: protein refolding
    locations:
      - id: GO:0005829
        label: cytosol
    description: >-
      SSA2 is the most abundant cytoplasmic Hsp70 in S. cerevisiae (364,000 molecules/cell),
      functioning as an ATP-dependent protein folding chaperone. It is 97% identical to SSA1
      and functionally interchangeable for refolding of denatured proteins (PMID:8947547).
      SSA2 uses ATP hydrolysis cycles to assist both de novo folding of newly translated
      proteins (PMID:9789005) and refolding of stress-denatured proteins (PMID:8947547,
      PMID:9448096). It cooperates with J-domain co-chaperones (Ydj1, Sis1), nucleotide
      exchange factors (Sse1/Sse2, Fes1), and Hsp90 (HSP82/HSC82). SSA2 also has specialized
      roles in tRNA nuclear import (PMID:25853343), ubiquitin-dependent protein degradation
      (PMID:27178214), and transcriptional regulation via the HAP1 repressor complex
      (PMID:15102838).

Gene Description

Existing Annotations Review

Core Functions

References

Deep Research

Falcon

Research report: Functional annotation of Saccharomyces cerevisiae SSA2 (UniProt P10592; YLL024C)

0) Target verification (mandatory)

1) Key concepts and definitions (current understanding)

1.1 What SSA2 encodes (primary function)

1.2 Canonical Hsp70 machine components relevant to SSA2

1.3 Domain-level functional mapping (alignment with UniProt domain architecture)

2) Cellular localization and where SSA2 acts

3) Pathways and biological processes involving SSA2

3.1 Hsp70–Hsp90 client processing and maturation

3.2 Heat shock response (HSR) feedback control involving SSA2 (2024 development)

3.3 Spatial proteostasis: JUNQ/IPOD sorting and microautophagy-linked clearance (2024 review)

4) Recent developments (prioritizing 2023–2024)

5) Current applications and real-world implementations

6) Expert opinions / analysis from authoritative sources (within the retrieved evidence)

7) Statistics and quantitative data (from cited studies)

8) Visual evidence (figures)

9) Evidence map (compact)

10) Limitations of this report (scope of retrieved evidence)

Artifacts

Citations

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