Cysteine-rich secretory protein 2 (CRISP2) is a testis-specific secretory protein that plays critical roles in male reproductive biology. It is incorporated into developing sperm during spermatogenesis and localizes primarily to the acrosome (particularly the equatorial segment), flagellum, and cytoplasmic droplet of mature sperm. CRISP2 functions as an ion channel regulator, particularly modulating calcium flux during sperm capacitation (including ryanodine receptor-mediated Ca2+ release), and is involved in the acrosome reaction and fertilization processes. The protein contains characteristic CAP and cysteine-rich (ShKT/CRISP) domains that mediate protein-protein interactions and ion channel regulation; recent biochemical evidence shows the CAP domain also binds sterols (e.g., cholesterol sulfate) and mediates sterol export, an activity inhibited by A1BG binding.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005615 extracellular space | IBA GO_REF:0000033 | ACCEPT | Summary: CRISP2 is a secretory protein that is released into extracellular space. The IBA annotation is based on phylogenetic inference across the CRISP family, which are characterized as secreted proteins. Reason: The annotation is correct and well-supported. CRISP2 contains a signal peptide (residues 1-21) and is annotated as "Secreted" in UniProt. The deep research confirms CRISP2 "is predicted to be active in the extracellular space, consistent with its secretory nature" and localizes to the acrosome and flagellum of sperm cells, which are extracellular compartments. The IBA evidence provides strong phylogenetic support across orthologous CRISP family members. Supporting Evidence: PMID:8665901 CRISP-2/TPX1 transcripts are...detected mainly in the testis and also in the epididymis file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is primarily localized to the acrosome and flagellum of sperm cells. It is predicted to be active in the extracellular space, consistent with its secretory nature file:human/CRISP2/CRISP2-uniprot.txt SUBCELLULAR LOCATION: Secreted file:human/CRISP2/CRISP2-deep-research-falcon.md In ejaculated sperm, CRISP2 is reported in the **cytoplasmic droplet**, **flagellum**, and **EqS**, consistent with roles in motility and gamete fusion |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: This is a broad extracellular localization term assigned by automated evidence based on InterPro domain signatures and UniProt subcellular location annotation. Reason: The annotation is correct as CRISP2 is a secreted protein found in extracellular regions. While GO:0005615 (extracellular space) is more specific, GO:0005576 (extracellular region) is also accurate and represents a valid parent term. The IEA annotation is appropriately conservative, providing broad localization information based on sequence features and subcellular location keywords. Having both the specific term (GO:0005615) and broader term (GO:0005576) is acceptable and provides complete annotation coverage. Supporting Evidence: GO_REF:0000120 Combined Automated Annotation using Multiple IEA Methods based on InterPro:IPR018244 and UniProtKB-SubCell:SL-0243 file:human/CRISP2/CRISP2-uniprot.txt SUBCELLULAR LOCATION: Secreted file:human/CRISP2/CRISP2-deep-research-falcon.md CRISPs as typically **two-domain proteins** comprising an N-terminal **CAP domain** plus a C-terminal **cysteine-rich CRISP domain** |
| GO:0005615 extracellular space | TAS PMID:8665901 The human cysteine-rich secretory protein (CRISP) family. Pr... | ACCEPT | Summary: This annotation is supported by the foundational characterization paper for the human CRISP family by Kraetzschmar et al. 1996, which described CRISP2 tissue distribution and confirmed it as a secreted protein. Reason: The TAS (Traceable Author Statement) annotation is well-founded. PMID:8665901 is the seminal paper characterizing CRISP2 (referred to as TPX1 in that work) as a secretory protein with testis and epididymis expression. The paper states "CRISP-2 cDNA corresponds to the previously described TPX1 form" and describes tissue distribution indicating secretory nature. While the abstract does not explicitly state "extracellular space," the characterization of CRISP proteins as secretory proteins with cysteine-rich domains supports extracellular localization. This represents core literature-based evidence for CRISP2 localization. Supporting Evidence: PMID:8665901 CRISP-2/TPX1 transcripts are...detected mainly in the testis and also in the epididymis... We report the isolation and characterisation of cDNAs encoding three different, human members of the cysteine-rich secretory protein (CRISP) family. file:human/CRISP2/CRISP2-deep-research-falcon.md In human epididymis, CRISP2 staining is observed in sperm within the lumen (including a dense spot at the basal head region and along the flagellum), while the epididymal epithelium is negative |
| GO:0005246 calcium channel regulator activity | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. Supporting Evidence: file:human/CRISP2/CRISP2-uniprot.txt May regulate some ion channels' activity and thereby regulate calcium fluxes during sperm capacitation. file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is predicted to regulate the activity of certain ion channels, particularly those involved in calcium fluxes during sperm capacitation, a process essential for fertilization file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is involved in the acrosome reaction, a key step in fertilization where the sperm releases enzymes to penetrate the egg file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is primarily localized to the acrosome and flagellum of sperm cells file:human/CRISP2/CRISP2-deep-research-falcon.md Review-level synthesis places CRISP2 in sperm Ca2+ signaling through **ryanodine receptor (RyR)-mediated Ca2+ release** and broader ion-channel modulation file:human/CRISP2/CRISP2-deep-research-falcon.md A 2023 ejaculate-based shotgun proteomics study explicitly annotates CRISP2 as potentially regulating **ion channels** and thereby **calcium fluxes during sperm capacitation** |
| GO:0001669 acrosomal vesicle | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. Supporting Evidence: file:human/CRISP2/CRISP2-uniprot.txt May regulate some ion channels' activity and thereby regulate calcium fluxes during sperm capacitation. file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is predicted to regulate the activity of certain ion channels, particularly those involved in calcium fluxes during sperm capacitation, a process essential for fertilization file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is involved in the acrosome reaction, a key step in fertilization where the sperm releases enzymes to penetrate the egg file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is primarily localized to the acrosome and flagellum of sperm cells file:human/CRISP2/CRISP2-deep-research-falcon.md Late elongated spermatids:** CRISP2 also seen in the **flagellum** and the **equatorial segment (EqS)** of the acrosome file:human/CRISP2/CRISP2-deep-research-falcon.md In ejaculated sperm, CRISP2 is reported in the **cytoplasmic droplet**, **flagellum**, and **EqS**, consistent with roles in motility and gamete fusion |
| GO:0048240 sperm capacitation | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. Supporting Evidence: file:human/CRISP2/CRISP2-uniprot.txt May regulate some ion channels' activity and thereby regulate calcium fluxes during sperm capacitation. file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is predicted to regulate the activity of certain ion channels, particularly those involved in calcium fluxes during sperm capacitation, a process essential for fertilization file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is involved in the acrosome reaction, a key step in fertilization where the sperm releases enzymes to penetrate the egg file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is primarily localized to the acrosome and flagellum of sperm cells file:human/CRISP2/CRISP2-deep-research-falcon.md A 2023 ejaculate-based shotgun proteomics study explicitly annotates CRISP2 as potentially regulating **ion channels** and thereby **calcium fluxes during sperm capacitation** |
| GO:0007340 acrosome reaction | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. Supporting Evidence: file:human/CRISP2/CRISP2-uniprot.txt May regulate some ion channels' activity and thereby regulate calcium fluxes during sperm capacitation. file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is predicted to regulate the activity of certain ion channels, particularly those involved in calcium fluxes during sperm capacitation, a process essential for fertilization file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is involved in the acrosome reaction, a key step in fertilization where the sperm releases enzymes to penetrate the egg file:human/CRISP2/CRISP2-deep-research-perplexity-lite.md CRISP2 is primarily localized to the acrosome and flagellum of sperm cells file:human/CRISP2/CRISP2-deep-research-falcon.md Late elongated spermatids:** CRISP2 also seen in the **flagellum** and the **equatorial segment (EqS)** of the acrosome |
| GO:0032934 sterol binding | NAS | NEW | Summary: Added based on 2024 biochemical evidence that the CRISP2 CAP domain binds cholesterol sulfate and mediates sterol export in a yeast assay; activity is inhibited by A1BG binding in a Mg2+-dependent manner. Reason: Novel mechanistic activity supported by PMID:39433128 (El Atab et al. 2024, J Biol Chem) demonstrating direct sterol binding via the CAP domain. This activity is not in current GOA but represents a credible biochemical function from a domain-leading peer-reviewed journal. Supporting Evidence: PMID:39433128 Alpha-1-b glycoprotein (a1bg) inhibits sterol-binding and export by crisp2 file:human/CRISP2/CRISP2-deep-research-falcon.md biochemical evidence that CRISP2 participates in **sterol binding and sterol export** in a yeast-based functional model and that this activity can be strongly regulated by A1BG file:human/CRISP2/CRISP2-deep-research-falcon.md Coexpression of A1BG with CRISP2 (or related CAP proteins) reduced sterol secretion by **>50%** in vivo (yeast export assay) |
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