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this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.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.
The gene symbol gpi16 is consistent with the supplied target: UniProt O94380, ORF SPBC1604.15, from Schizosaccharomyces pombe strain 972/ATCC 24843. Published sequence comparisons explicitly recognize an S. pombe Gpi16 homolog, and the designation agrees with the conserved correspondence fungal Gpi16 ↔ mammalian PIG-T. The supplied PIG-T/Gpi16 domain assignments—InterPro PIG-T and Pfam Gpi16—therefore fit the literature. No evidence suggesting that this is an unrelated same-symbol gene was found. However, literature directly examining O94380/SPBC1604.15 is very limited; most mechanistic annotation necessarily derives from Saccharomyces cerevisiae Gpi16 and mammalian PIG-T orthologs. (fraering2001thegpitransamidase pages 4-5, zacks2006recentdevelopmentsin pages 10-11)
The best-supported annotation is: an endoplasmic-reticulum membrane component of the heteropentameric GPI transamidase complex, required for efficient recognition, positioning, and covalent GPI anchoring of precursor proteins, but not itself the catalytic cysteine protease. An independent catalytic reaction should not be assigned to Gpi16.
| Annotation claim | Best evidence | Evidence species/system | Confidence |
|---|---|---|---|
| Identity: O94380 is gpi16 / SPBC1604.15, a PIG-T-family Gpi16 homolog | The supplied UniProt identity is consistent with a published sequence comparison explicitly listing an S. pombe Gpi16 homolog; conserved correspondence is yeast Gpi16 ↔ mammalian PIG-T. No conflicting same-symbol protein was used. (fraering2001thegpitransamidase pages 4-5, zacks2006recentdevelopmentsin pages 10-11) | S. pombe sequence annotation plus cross-eukaryotic homology | High for family assignment; database-based for exact accession/ORF mapping |
| Primary function: noncatalytic component of GPI transamidase (GPIT), not the catalytic protease | S. cerevisiae Gpi16 copurifies with Gpi8 and Gaa1; conserved complexes contain Gpi8/GPI16/Gaa1/Gpi17/Gab1. Gpi8/PIG-K—not Gpi16/PIG-T—contains the catalytic cysteine-protease machinery. (gamage2013gpitransamidaseand pages 7-8, fraering2001thegpitransamidase pages 4-5, ness2022asolubleminimalistic pages 2-3, humphreys2021computedstructuresof pages 9-11) | Direct S. cerevisiae complex biochemistry; mammalian/conserved mechanism; orthology-based for S. pombe | High |
| Localization/topology: ER-resident, type-I single-pass membrane protein with a large ER-luminal domain and C-terminal transmembrane segment | Conserved Gpi16/PIG-T is predicted and experimentally contextualized as a type-I ER membrane subunit with one C-terminal transmembrane helix; yeast homologs may use a short cytosolic ER-retrieval signal. (zacks2006recentdevelopmentsin pages 10-11, ness2022asolubleminimalistic pages 2-3, gamage2013gpitransamidaseand pages 6-7) | Yeast/mammalian homologs; orthology-based prediction for O94380 | Moderate–high |
| Structural role: contributes to substrate-signal recognition and GPIT organization/stability | Structural modeling places Gpi16 beside Gpi8 and Gpi17 in a tunnel proposed to receive the substrate’s C-terminal GPI-attachment signal. Pairwise-complex and knockout evidence supports interactions with Gpi8/Gaa1 and stabilization of other subunits. (gamage2013gpitransamidaseand pages 7-8, ness2022asolubleminimalistic pages 2-3) | S. cerevisiae biochemical/computational studies and mammalian structures; orthology-based for S. pombe | Moderate–high; exact contribution remains incompletely resolved |
| Reaction: GPIT replaces a substrate protein’s C-terminal GPI signal peptide with preassembled GPI | The whole complex cleaves after the ω residue, forms a Gpi8–substrate thioester intermediate, and transfers the protein carbonyl to the terminal ethanolamine-phosphate amino group of GPI, creating an amide bond. Gpi16 supports this reaction but is not assigned an independent catalytic reaction. (gamage2013gpitransamidaseand pages 5-6, ness2022asolubleminimalistic pages 2-3, humphreys2021computedstructuresof pages 9-11) | Conserved yeast/mammalian GPIT mechanism; orthology-based for S. pombe | High for complex reaction; high that Gpi16 is noncatalytic |
| Substrate specificity: proteins bearing a lumen-exposed C-terminal GPI-attachment signal, rather than one named protein substrate | Recognition depends on an ω-site region, hydrophilic spacer, and terminal hydrophobic segment rather than a strict sequence consensus; the GPI cosubstrate is a preassembled, ethanolamine-phosphate-terminated anchor. (gamage2013gpitransamidaseand pages 5-6, ness2022asolubleminimalistic pages 2-3) | Mammalian/yeast mechanistic studies; orthology-based for S. pombe | High at the signal-class level; individual S. pombe clients uncharacterized |
| Evidence limitation: no direct biochemical characterization of S. pombe O94380 was identified | Retrieved target-specific evidence establishes homology, but complex purification, topology, catalytic-assay, mutational, and structural results concern S. cerevisiae or mammalian homologs. (fraering2001thegpitransamidase pages 4-5, nordlin2023productionpurificationanda pages 11-15, nordlin2023productionpurificationand pages 11-15, ness2022asolubleminimalistic pages 2-3) | Literature search outcome | High |
Table: Evidence grading for the proposed functional annotation of S. pombe gpi16/O94380. It distinguishes target-specific identification from mechanistic conclusions inferred through conserved yeast and mammalian orthologs.
The literature uses Gpi16 for the fungal homolog of mammalian PIG-T. A foundational S. cerevisiae transamidase study included an S. pombe Gpi16 homolog in its sequence comparison, supporting the family assignment independently of the supplied annotation. That study did not, however, experimentally investigate O94380 itself. (fraering2001thegpitransamidase pages 4-5)
Accordingly, the following evidence grades should be maintained:
Thus, the gene is not ambiguous in the available context, but target-specific experimental literature is sparse.
GPI transamidase, abbreviated GPIT or GPI-T, is the ER enzyme complex that covalently attaches a preassembled glycosylphosphatidylinositol anchor to the C terminus of an appropriate precursor protein. In budding yeast the mature complex consists of Gpi8, Gaa1, Gpi16, Gpi17 and Gab1/Cdc91; the corresponding mammalian proteins are PIG-K, GPAA1, PIG-T, PIG-S and PIG-U. Direct affinity purification in S. cerevisiae recovered Gpi16 with Gpi8 and Gaa1, establishing Gpi16 as a physical component of the complex. Early preparations migrated at approximately 430–650 kDa, substantially above the calculated mass of the initially recognized three-subunit assembly and consistent with a larger or oligomeric membrane complex. These experiments concern budding yeast, not S. pombe. (fraering2001thegpitransamidase pages 4-5, gamage2013gpitransamidaseand pages 5-6, humphreys2021computedstructuresof pages 9-11)
Catalytic cleavage of the precursor protein is assigned to Gpi8/PIG-K, a C13-family cysteine-protease-like subunit containing the catalytic cysteine–histidine machinery. Gpi16/PIG-T lacks that established catalytic assignment. Instead, PIG-T is required for full formation or productive use of the Gpi8–substrate acyl intermediate and contributes to complex organization and substrate handling. Loss of mammalian PIG-T also reduces levels of other GPIT components, supporting a stabilizing or assembly role. (gamage2013gpitransamidaseand pages 7-8, ness2022asolubleminimalistic pages 2-3, gamage2013gpitransamidaseand pages 6-7)
In mammals and trypanosomes, conserved cysteines in PIG-T and PIG-K form an intermolecular disulfide bond. Mutating the relevant cysteines reduced in-vitro transamidase activity and restoration of cell-surface GPI-anchored proteins, although the linkage was not absolutely required for complex assembly. Importantly, S. cerevisiae studies did not reproduce a Gpi8–Gpi16 disulfide and instead found species-specific interaction behavior. It would therefore be unsafe to annotate such a disulfide bond as experimentally established in S. pombe. (gamage2013gpitransamidaseand pages 7-8)
The net GPIT reaction is:
GPI-signal-bearing precursor protein + preassembled GPI → mature protein–C(O)–NH–CH₂–CH₂–phosphate–GPI + cleaved C-terminal signal peptide.
Mechanistically, Gpi8 cleaves the precursor between the amino acid designated the ω residue and ω+1. Its catalytic cysteine forms a transient thioester with the new protein C terminus. The terminal ethanolamine-phosphate amino group of preassembled GPI then attacks this intermediate, producing the final amide linkage. A soluble S. cerevisiae heterotrimer containing truncated Gpi8, Gaa1 and Gpi16 retained transamidation activity in a synthetic-peptide assay, showing that these soluble domains can support core chemistry outside the complete membrane pentamer. (ness2022asolubleminimalistic pages 2-3, humphreys2021computedstructuresof pages 9-11)
For annotation purposes, this is the reaction of the GPIT complex, not a separately demonstrated catalytic reaction of Gpi16. Gpi16 should therefore be described as an essential or facilitating transamidase component rather than as “the GPI transamidase enzyme” acting alone.
The protein substrates are secretory-pathway precursors that have entered the ER lumen and carry a suitable C-terminal GPI-attachment signal. Recognition does not depend on one strict consensus sequence. Instead, it reflects a signal architecture including an accessible ω-site region, residues compatible with cleavage near ω, an intervening hydrophilic segment, and a terminal hydrophobic segment. Consequently, Gpi16 is not expected to recognize one metabolite or one named protein; it participates in recognizing a structural class of precursor proteins. (gamage2013gpitransamidaseand pages 5-6, humphreys2021computedstructuresof pages 9-11)
The lipid cosubstrate is a preassembled GPI anchor bearing terminal ethanolamine phosphate, whose free amino group becomes linked to the substrate’s newly generated C terminus. The available studies do not establish whether S. pombe Gpi16 makes direct, sequence-specific contact with particular native clients.
GPIT acts in the endoplasmic reticulum, with precursor processing and GPI transfer occurring on the luminal side of the ER membrane. Conserved Gpi16/PIG-T proteins are type-I, single-pass membrane proteins with a large N-terminal luminal region and one C-terminal transmembrane helix, leaving only a short cytosolic tail. Yeast homologs have also been reported to contain a short cytosolic ER-retrieval signal near the C terminus. This topology places Gpi16’s principal domain in the correct compartment to contact luminal precursor proteins and other GPIT subunits. (zacks2006recentdevelopmentsin pages 10-11, ness2022asolubleminimalistic pages 2-3, gamage2013gpitransamidaseand pages 6-7)
For O94380, ER residence is highly credible but orthology-based; no retrieved paper directly imaged or biochemically fractionated S. pombe Gpi16. The protein description’s “precursor” flag should not be interpreted as evidence that Gpi16 itself is secreted. Rather, its predicted membrane topology is consistent with insertion into the ER membrane and retention as an integral component of the ER machinery.
A 2021 deep-learning/co-evolution study modeled 8.3 million pairs of budding-yeast proteins, ultimately constructing models for 106 previously unidentified and 806 previously structurally uncharacterized assemblies. Its S. cerevisiae GPIT model placed the catalytic Gpi8 site adjacent to a channel formed with noncatalytic subunits, providing a structural rationale for coordinated recognition of the hydrophobic C-terminal GPI signal. Published December 2021, DOI: https://doi.org/10.1126/science.abm4805. (humphreys2021computedstructuresof pages 9-11)
Subsequent structural comparison and biochemical work placed Gpi16 alongside Gpi8 and Gpi17 in the proposed precursor-signal tunnel. In comparisons of soluble yeast and human domains, structural RMSDs were 0.770 Å for Gpi8, 0.858 Å for Gaa1 and 1.182 Å for Gpi16, indicating strong conservation of the core architecture. A truncated soluble Gpi8–Gaa1–Gpi16 heterotrimer remained active, providing experimental support for functional cooperation among these three domains. Published June 2022, DOI: https://doi.org/10.1021/acs.biochem.2c00196. (ness2022asolubleminimalistic pages 2-3)
The most defensible expert interpretation is therefore that Gpi16 is a scaffolding and substrate-positioning subunit. Its luminal domain helps build the passage that receives the precursor’s C-terminal signal and positions it relative to catalytic Gpi8 and other components. Calling it merely “structural” may understate its functional importance, but assigning it protease or transferase chemistry would overstate the evidence.
The direct pathway is GPI-anchor attachment to proteins, the terminal transfer stage of GPI-anchored-protein biogenesis. After modification in the ER, successfully anchored proteins enter the secretory pathway and can reach the plasma membrane or, in fungi, become incorporated into the cell-wall environment. The broader GPI-biosynthesis pathway requires approximately 10–11 reactions and at least 23 proteins, emphasizing that Gpi16 acts at one late, highly coordinated step rather than synthesizing the lipid anchor itself. (nordlin2023productionpurificationanda pages 11-15, nordlin2023productionpurificationanda pages 8-11)
In fungi, GPI-anchored proteins commonly support cell-surface and cell-wall functions, and disruption of GPI biogenesis is associated across yeast systems with growth impairment, abnormal morphology and cell-wall defects. These outcomes explain why a Gpi16 defect could be pleiotropic, but they do not identify Gpi16 as a signaling protein. Its primary role is biochemical—protein lipidation in the ER—not signal transduction. (nordlin2023productionpurificationanda pages 8-11)
For S. pombe, effects on cell-wall integrity, morphology or separation are biologically plausible downstream consequences because this organism uses GPI-anchored surface proteins. Nevertheless, no retrieved study directly connected an O94380 mutation to those phenotypes, so they should not be entered as experimentally verified gene-specific functions.
No 2023–2024 primary paper directly characterizing S. pombe O94380/SPBC1604.15 was identified. The latest decisive advances available for mechanistic annotation are instead the 2021 computed pentameric architecture, the 2022 human cryo-EM era, and the 2022 soluble minimal-complex assay. A 2024 expert chapter, Structure and function of the glycosylphosphatidylinositol transamidase, a transmembrane complex catalyzing GPI anchoring of proteins, provides an updated synthesis (published 2024; DOI: https://doi.org/10.1007/978-3-031-58843-3_16), but target-specific S. pombe data remain absent.
This gap is itself important for annotation: recent structures strengthen the conserved mechanistic model but do not replace organism-specific validation. Particularly valuable future experiments would be endogenous tagging and ER colocalization, co-immunoprecipitation with predicted S. pombe GPIT partners, conditional depletion followed by GPI-anchored-protein profiling, and complementation with catalytic-site-independent Gpi16 variants.
O94380 can be used as a conserved ER-protein-processing marker or perturbation point in fission-yeast studies of GPI-anchored-protein biogenesis. Because the protein is a noncatalytic complex component, depletion may test assembly and substrate-recognition functions without directly mutating the Gpi8 catalytic center.
The active soluble Gpi8–Gaa1–Gpi16 complex provides a quantitative platform for testing GPIT activity and screening inhibitors. Gpi16-containing assemblies may therefore support biochemical assay development even if Gpi16 is not itself the catalytic target. (ness2022asolubleminimalistic pages 2-3)
Fungal GPI anchoring is attractive for antifungal discovery because many fungal GPI-anchored proteins are important for cell-wall construction and viability. However, conservation with the human complex creates selectivity concerns. There is currently no evidence that S. pombe Gpi16 is a clinically implemented drug target, and the organism itself is principally a research model rather than a major human pathogen.
Human PIG-T is a conserved ortholog, and GPIT defects affect cell-surface display of numerous GPI-anchored proteins. Such human findings establish the biomedical importance of the molecular machine but should not be conflated with evidence about fission-yeast O94380.
Name: GPI transamidase component Gpi16; PIG-T homolog.
Molecular function: Noncatalytic component of the ER GPI transamidase complex; contributes to precursor-signal recognition, substrate positioning, complex organization and efficient GPI transfer.
Process: GPI-anchor attachment to proteins; GPI-anchored-protein maturation in the ER.
Localization: Integral ER membrane protein, probably type-I single-pass, with a large luminal PIG-T/Gpi16 domain and C-terminal membrane anchor.
Substrates: As part of GPIT, ER-luminal precursor proteins bearing C-terminal GPI-attachment signals and a preassembled ethanolamine-phosphate-terminated GPI anchor.
Catalytic qualification: No independent catalytic activity established; Gpi8 is the cysteine-protease catalytic subunit.
Evidence qualifier: Strongly supported by conserved-family, budding-yeast biochemical and mammalian structural evidence; direct biochemical validation in S. pombe remains lacking.
References
(fraering2001thegpitransamidase pages 4-5): Patrick Fraering, Isabella Imhof, Urs Meyer, Jean-Marc Strub, Alain van Dorsselaer, Christine Vionnet, and Andreas Conzelmann. The gpi transamidase complex of saccharomyces cerevisiae contains gaa1p, gpi8p, and gpi16p. Molecular biology of the cell, 12 10:3295-306, Oct 2001. URL: https://doi.org/10.1091/mbc.12.10.3295, doi:10.1091/mbc.12.10.3295. This article has 146 citations and is from a domain leading peer-reviewed journal.
(zacks2006recentdevelopmentsin pages 10-11): Michele A. Zacks and Nisha Garg. Recent developments in the molecular, biochemical and functional characterization of gpi8 and the gpi-anchoring mechanism [review]. Molecular Membrane Biology, 23:209-225, Jan 2006. URL: https://doi.org/10.1080/09687860600601494, doi:10.1080/09687860600601494. This article has 52 citations and is from a peer-reviewed journal.
(gamage2013gpitransamidaseand pages 7-8): Dilani G. Gamage and Tamara L. Hendrickson. Gpi transamidase and gpi anchored proteins: oncogenes and biomarkers for cancer. Critical Reviews in Biochemistry and Molecular Biology, 48:446-464, Sep 2013. URL: https://doi.org/10.3109/10409238.2013.831024, doi:10.3109/10409238.2013.831024. This article has 69 citations and is from a peer-reviewed journal.
(ness2022asolubleminimalistic pages 2-3): Travis J. Ness, Dilani G. Gamage, Sandamali A. Ekanayaka, and Tamara L. Hendrickson. A soluble, minimalistic glycosylphosphatidylinositol transamidase (gpi-t) retains transamidation activity. Biochemistry, 61:1273-1285, Jun 2022. URL: https://doi.org/10.1021/acs.biochem.2c00196, doi:10.1021/acs.biochem.2c00196. This article has 11 citations and is from a peer-reviewed journal.
(humphreys2021computedstructuresof pages 9-11): Ian R. Humphreys, Jimin Pei, Minkyung Baek, Aditya Krishnakumar, Ivan Anishchenko, Sergey Ovchinnikov, Jing Zhang, Travis J. Ness, Sudeep Banjade, Saket R. Bagde, Viktoriya G. Stancheva, Xiao-Han Li, Kaixian Liu, Zhi Zheng, Daniel J. Barrero, Upasana Roy, Jochen Kuper, Israel S. Fernández, Barnabas Szakal, Dana Branzei, Josep Rizo, Caroline Kisker, Eric C. Greene, Sue Biggins, Scott Keeney, Elizabeth A. Miller, J. Christopher Fromme, Tamara L. Hendrickson, Qian Cong, and David Baker. Computed structures of core eukaryotic protein complexes. Dec 2021. URL: https://doi.org/10.1126/science.abm4805, doi:10.1126/science.abm4805. This article has 607 citations and is from a highest quality peer-reviewed journal.
(gamage2013gpitransamidaseand pages 6-7): Dilani G. Gamage and Tamara L. Hendrickson. Gpi transamidase and gpi anchored proteins: oncogenes and biomarkers for cancer. Critical Reviews in Biochemistry and Molecular Biology, 48:446-464, Sep 2013. URL: https://doi.org/10.3109/10409238.2013.831024, doi:10.3109/10409238.2013.831024. This article has 69 citations and is from a peer-reviewed journal.
(gamage2013gpitransamidaseand pages 5-6): Dilani G. Gamage and Tamara L. Hendrickson. Gpi transamidase and gpi anchored proteins: oncogenes and biomarkers for cancer. Critical Reviews in Biochemistry and Molecular Biology, 48:446-464, Sep 2013. URL: https://doi.org/10.3109/10409238.2013.831024, doi:10.3109/10409238.2013.831024. This article has 69 citations and is from a peer-reviewed journal.
(nordlin2023productionpurificationanda pages 11-15): P Nordlin. Production, purification, and characterization of recombinant gpi3-a catalytic subunit involved in gpi biosynthesis. Unknown journal, 2023.
(nordlin2023productionpurificationand pages 11-15): P Nordlin. Production, purification, and characterization of recombinant gpi3-a catalytic subunit involved in gpi biosynthesis. Unknown journal, 2023.
(nordlin2023productionpurificationanda pages 8-11): P Nordlin. Production, purification, and characterization of recombinant gpi3-a catalytic subunit involved in gpi biosynthesis. Unknown journal, 2023.