GLIPR1L1 is a testis-enriched, secretory-pathway CAP/CRISP-family protein produced as a precursor with an N-terminal signal peptide and a predicted C-terminal GPI anchor. Mammalian ortholog studies place GLIPR1L1 on the sperm head plasma membrane, acrosomal region, membrane rafts, and connecting piece. In mouse sperm it associates directly with IZUMO1 in maturation-dependent, high-molecular-weight oolemma-binding complexes and promotes IZUMO1 redistribution during the acrosome reaction, thereby supporting optimal sperm-oocyte membrane fusion. This role is modulatory rather than essential: mouse single-gene loss impairs acrosome reaction and in-vitro fertilization, whereas natural fertility remains intact even after deletion of all three neighboring Glipr1-like genes. Direct functional characterization of the endogenous human protein remains limited.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference places GLIPR1L1 in the extracellular region, which is consistent with its signal peptide, predicted GPI anchor, and the extracellular sperm-surface localization of mammalian orthologs. Reason: A GPI-anchored sperm-surface protein acts on the non-cytoplasmic side of the plasma membrane. Direct bovine experiments and mouse sperm-surface localization independently support this broad IBA assignment, and the human sequence retains the required secretory-pathway features. Supporting Evidence: PMID:22552861 GliPr1L1 is glycosyl phosphatidyl inositol (GPI) anchored to caput and cauda spermatozoa |
| GO:0060090 molecular adaptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: GLIPR1L1 is inferred to act as a nonenzymatic organizer of an IZUMO1-containing sperm-surface complex during acrosome remodeling. Reason: Mouse GLIPR1L1 directly co-immunoprecipitates with IZUMO1, occurs with it in several high-molecular-weight complexes, and is required for normal IZUMO1 redistribution after acrosomal exocytosis. Molecular adaptor activity captures this bridging/organizing role without asserting an unproven direct fusogenic activity. Transfer to the conserved human ortholog is supported by the IBA tree and shared testis-enriched CAP architecture. Supporting Evidence: PMID:31672133 Firstly, co-immunoprecipitation using the IZUMO1 antibody from lysates of acrosome-reacted spermatozoa pulled down GLIPR1L1, and a reciprocal co-immunoprecipitation with the GLIPR1L1 antibody successfully isolated IZUMO1 PMID:31672133 our data show that the movement of IZUMO1 is dependent on GLIPR1L1 function file:human/GLIPR1L1/GLIPR1L1-deep-research-manual.md The core inferred human activity is molecular adaptor activity at acrosomal/sperm-head membrane rafts as part of an IZUMO1-containing adhesion complex, directly contributing to IZUMO1 localization during the acrosome reaction and supporting sperm–egg plasma-membrane fusion. |
| GO:0001669 acrosomal vesicle | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping assigns the acrosomal-vesicle localization inferred from the mouse ortholog. Reason: Mouse GLIPR1L1 localizes to the peri-acrosomal/anterior sperm-head region and redistributes during the acrosome reaction. Human GLIPR1L1 is strongly testis enriched and has the same secretory-pathway CAP-family architecture, making the conservative acrosomal-vesicle mapping credible. Supporting Evidence: PMID:31672133 Both proteins displayed strong colocalization with GM1 gangliosides in the peri-acrosomal region of the head of capacitated spermatozoa |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: The combined automated annotation integrates the extracellular CAP-domain family signature and UniProt secretory-location mapping. Reason: The term is broad but correct for a signal-peptide-bearing, predicted GPI-anchored protein that acts at the extracellular face of the sperm plasma membrane. Ortholog experiments provide independent localization support. Supporting Evidence: PMID:22552861 Western blots demonstrated that GliPr1L1 was associated with the sperm plasma membrane preparation |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt maps its sperm-surface localization statement to plasma membrane. Reason: Direct bovine biochemical fractionation and GPI-anchor release place GLIPR1L1 at the sperm plasma membrane, while mouse experiments place the ortholog in live sperm-surface rafts. The human protein has a predicted GPI anchor, supporting conservation of this location. Supporting Evidence: PMID:22552861 Western blots demonstrated that GliPr1L1 was associated with the sperm plasma membrane preparation |
| GO:0045121 membrane raft | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping assigns a membrane-raft location from mammalian sperm studies. Reason: Bovine GLIPR1L1 was biochemically recovered in sperm lipid-raft fractions, and mouse GLIPR1L1 colocalized with the GM1 raft marker in live capacitated sperm. Concordance in two mammalian orthologs plus the predicted human GPI anchor makes the mapping well supported. Supporting Evidence: PMID:22552861 GliPr1L1 was immunodetectable in the low buoyant density fractions where lipid rafts are distributed PMID:31672133 Both proteins displayed strong colocalization with GM1 gangliosides in the peri-acrosomal region of the head of capacitated spermatozoa |
| GO:0005576 extracellular region | ISS GO_REF:0000024 | ACCEPT | Summary: Curator-judged transfer from mouse Q9DAG6 assigns the extracellular sperm-surface pool to human GLIPR1L1. Reason: The orthology transfer agrees with the human signal peptide and predicted GPI anchor and with independent bovine sperm-surface evidence. Although secretion/acquisition routes vary between species, an extracellular-facing pool is consistently supported. Supporting Evidence: PMID:31672133 GLIPR1L1 is also present on the plasma membrane of at least rat, bovine, and macaque sperm |
| GO:0005886 plasma membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Curator-judged transfer from mouse Q9DAG6 places human GLIPR1L1 at the sperm plasma membrane. Reason: Mouse and bovine experiments independently identify sperm-surface pools, and the predicted human GPI-anchor signal provides sequence-level corroboration. Species differ in how GLIPR1L1 reaches the surface, not in the existence of a sperm plasma-membrane pool. Supporting Evidence: PMID:22552861 Western blots demonstrated that GliPr1L1 was associated with the sperm plasma membrane preparation |
| GO:0045121 membrane raft | ISS GO_REF:0000024 | ACCEPT | Summary: Curator-judged transfer from bovine Q32LB5 places the human ortholog in sperm membrane rafts. Reason: The bovine lipid-raft fractionation is direct, and the same localization was subsequently observed by GM1 colocalization in live mouse sperm. This cross-species agreement makes the human ISS assignment credible. Supporting Evidence: PMID:22552861 GliPr1L1 was immunodetectable in the low buoyant density fractions where lipid rafts are distributed |
| GO:0001669 acrosomal vesicle | ISS GO_REF:0000024 | ACCEPT | Summary: Curator-judged transfer from mouse Q9DAG6 places human GLIPR1L1 in the sperm acrosomal region. Reason: Direct mouse imaging shows peri-acrosomal/anterior-head GLIPR1L1 and its dynamic redistribution after acrosomal exocytosis. Testis-enriched human expression and conserved orthology support this conservative transfer. Supporting Evidence: PMID:20219979 After sperm capacitation, however, GLIPR1L1 is also localized to the anterior regions of the sperm head |
| GO:0007342 fusion of sperm to egg plasma membrane involved in single fertilization | ISS GO_REF:0000024 | ACCEPT | Summary: Curator-judged transfer from mouse Q9DAG6 assigns a role in sperm-oocyte membrane fusion to human GLIPR1L1. Reason: Mouse Glipr1l1 loss leaves zona-pellucida binding intact but reduces two-cell embryos after IVF, localizing the defect to a later fertilization stage. The annotation denotes participation, not absolute requirement, so it remains compatible with normal natural fertility in single- and triple-knockout mice. Supporting Evidence: PMID:31672133 the loss of Glipr1l1 did not affect the ability of sperm to bind to the zona pellucida, but did significantly reduced their ability to fertilize oocytes PMID:40572022 depletion of all three genes does not significantly affect male fertility |
| GO:0098635 protein complex involved in cell-cell adhesion | ISS GO_REF:0000024 | ACCEPT | Summary: Curator-judged transfer from mouse Q9DAG6 places human GLIPR1L1 in an IZUMO1-containing sperm adhesion complex. Reason: In mouse sperm, mass spectrometry, native electrophoresis, reciprocal immunoprecipitation, and proximity ligation support GLIPR1L1-IZUMO1 complex membership, and the high-molecular-weight complex binds oolemmal proteins. The precise additional components remain unknown, but the complex-level annotation is well supported for the ortholog. Supporting Evidence: PMID:31672133 Collectively, these results confirm that IZUMO1 and GLIPR1L1 form a protein complex within male germ cells |
| GO:0060476 protein localization involved in acrosome reaction | ISS PMID:31672133 GLIPR1L1 is an IZUMO-binding protein required for optimal fe... | NEW | Summary: Proposed human annotation by orthology. Mouse Glipr1l1 loss severely attenuates IZUMO1 redistribution across the sperm head after the acrosome reaction. Reason: This is the most specific process term for the directly observed adaptor consequence. It avoids overinterpreting GLIPR1L1 as the membrane fusogen while capturing its causal role in acrosome-reaction-dependent IZUMO1 localization. Assignment to human is by mammalian orthology. Supporting Evidence: PMID:31672133 Specifically, in WT sperm following the acrosome reaction, IZUMO1 was relocated throughout the sperm head in 85% of sperm, compared to 21% of acrosome-reacted Glipr1l1−/− sperm |
| GO:0120212 sperm head-tail coupling apparatus | ISS PMID:31672133 GLIPR1L1 is an IZUMO-binding protein required for optimal fe... | NEW | Summary: Proposed human annotation by orthology. Mouse GLIPR1L1 localizes to the sperm connecting piece, the region corresponding to the head-tail coupling apparatus. Reason: The connecting-piece localization was observed independently in the 2010 characterization and the 2019 knockout-controlled imaging study. It is a credible additional location for the conserved human ortholog, although no distinct function at this site is yet established. Supporting Evidence: PMID:31672133 additional GLIPR1L1 labeling was detected in a discrete spot at the posterior aspect of the sperm head corresponding to the connecting piece |
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Download this section (compressed HTML)Q: Does endogenous human GLIPR1L1 occupy the acrosomal membrane, sperm-head plasma membrane rafts, connecting piece, and an IZUMO1-containing complex in the same maturation-dependent pattern observed in mouse?
Suggested experts: Brett Nixon, Moira O'Bryan
Q: What molecules besides IZUMO1 contact GLIPR1L1, and does GLIPR1L1 bridge partners, organize membrane domains, or directly alter membrane biophysics?
Suggested experts: Brett Nixon
Q: Do the human GLIPR1L1alpha and GLIPR1L1beta isoforms differ in GPI-anchor processing, sperm localization, complex assembly, or acrosome-reaction function?
Suggested experts: Thomas Thompson
Q: Is human GLIPR1L1 delivered to sperm during spermatogenesis, transferred by epididymal extracellular vesicles, or present through both routes?
Suggested experts: Robert Sullivan
Experiment: Endogenously tag each GLIPR1L1 isoform in human testis organoids and analyze its appearance during germ-cell maturation; complement this with super-resolution imaging and detergent-free raft fractionation of donor sperm.
Hypothesis: Human GLIPR1L1 is processed into a GPI-anchored sperm-head protein enriched in acrosomal membrane rafts, with isoform-dependent abundance or trafficking.
Type: isoform-specific genome editing, organoid differentiation, microscopy, and membrane proteomics
Experiment: In donor human sperm, acutely block or enzymatically release GLIPR1L1 and quantify progesterone-induced acrosome reaction, IZUMO1 redistribution, and binding to recombinant JUNO-bearing supported membranes, with matched nonimmune and unrelated GPI-protein controls.
Hypothesis: Human GLIPR1L1 promotes acrosome-reaction-dependent IZUMO1 redistribution and efficient engagement of an oolemma-like membrane without being absolutely required.
Type: perturbation, quantitative imaging, flow cytometry, and membrane-binding assay
Experiment: Reconstitute purified human GLIPR1L1 and IZUMO1 in composition-controlled membranes and identify additional partners by cross-linking mass spectrometry; test complex formation, lateral redistribution, membrane curvature, and fusion.
Hypothesis: GLIPR1L1 acts as an adaptor or membrane-domain organizer for IZUMO1 rather than as an autonomous membrane fusogen.
Type: biochemical reconstitution, structural proteomics, and membrane biophysics
Experiment: Replace mouse Glipr1l1 with each human isoform on the Glipr1l1-null background and assay acrosome reaction, IZUMO1 redistribution, IVF, and natural fertility.
Hypothesis: At least one human isoform rescues the subtle mouse acrosome-reaction and IVF phenotypes, establishing functional conservation despite dispensability for natural fertility.
Type: mouse humanization and isoform-resolved functional rescue
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The precise molecular activity of GLIPR1L1 within the IZUMO1-containing complex is unknown.
OPEN BIOLOGYCURATION MF_DARK
What is known: Complex membership, direct IZUMO1 interaction, and GLIPR1L1-dependent IZUMO1 redistribution support molecular adaptor activity, but they do not distinguish direct bridging, membrane-domain organization, or an intrinsic effect on membrane fusion.
Significance: Resolving this mechanism would determine whether molecular adaptor activity is sufficient or whether a more specific molecular-function term is needed.
What would resolve it: Define the full complex by endogenous cross-linking proteomics, map direct binding interfaces, and test purified components in membrane-reconstitution assays.
Provenance (the field's own admissions):
Gap: Endogenous human GLIPR1L1 localization, IZUMO1 interaction, and fertilization function have not been directly demonstrated.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: Human evidence establishes sequence and reproductive-tissue expression; the functional annotation is transferred from mouse and bovine orthologs whose localization is concordant but whose membrane-acquisition mechanisms differ.
Significance: Direct human evidence is required to establish that the conserved ortholog model applies to human sperm and to assess clinical relevance.
What would resolve it: Combine isoform-specific antibodies or endogenous tagging with human sperm imaging, complex proteomics, acrosome-reaction perturbation, and non-clinical oolemma-mimetic assays.
Provenance (the field's own admissions):
Gap: The route by which human GLIPR1L1 reaches the sperm surface is unresolved.
OPEN BIOLOGY CC_DARK
What is known: Bovine GLIPR1L1 is transferred in epididymal microvesicles and is GPI anchored, whereas mouse GLIPR1L1 is acquired during spermatogenesis and lacks the same GPI-anchor mechanism; human GLIPR1L1 has a predicted GPI anchor but no direct trafficking study.
Significance: The trafficking route may determine isoform processing, membrane-raft incorporation, and when GLIPR1L1 can assemble with IZUMO1.
What would resolve it: Track isoform-specific GLIPR1L1 through human spermatogenesis and epididymal extracellular-vesicle exposure, using glycan/GPI-anchor profiling and pulse-chase proteomics.
Provenance (the field's own admissions):
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