PRRT1 (Proline-rich transmembrane protein 1), also known as SynDIG4 (Synapse differentiation-induced protein 4), is a single-pass type II transmembrane protein that functions as an auxiliary subunit of AMPA receptor (AMPAR) complexes. It belongs to the CD225/Dispanin family. PRRT1 regulates AMPAR trafficking, gating, and synaptic availability through mechanisms including: (1) direct modulation of AMPAR gating by slowing deactivation of GluA1 homomers and GluA1/2 heteromers and reducing desensitization; (2) regulation of AMPAR endocytic recycling via its YxxPhi endocytic motif (YVPV) that binds the AP-2 mu2 cargo-sorting subunit; and (3) maintaining extrasynaptic AMPAR pools through Rab4/Rab11-dependent endosomal recycling. Loss of SynDIG4 impairs basal AMPAR recycling, reduces synaptic surface GluA1, and abolishes single-tetanus-induced LTP and NMDAR-dependent LTD, leading to deficits in hippocampal-dependent learning and memory.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0030545
signaling receptor regulator activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: PRRT1/SynDIG4 directly modulates AMPA receptor (AMPAR) function as an auxiliary subunit. It binds to AMPAR complexes and regulates their gating properties, slowing deactivation and reducing desensitization. This constitutes regulation of a signaling receptor (AMPAR is an ionotropic glutamate receptor). The term is appropriate as PRRT1 modulates receptor activity rather than acting as the receptor itself (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: SynDIG4 functions as an AMPAR auxiliary factor that co-purifies with native AMPAR complexes and modulates gating (file:human/PRRT1/PRRT1-deep-research-falcon.md). Evidence shows it slows deactivation of GluA1 homomers and GluA1/2 heteromers and reduces desensitization of GluA1. IBA annotations have undergone phylogenetic review and this function is well-supported by the conserved role across orthologs.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 co-purifies with native AMPAR complexes and modulates gating. Evidence indicates it slows deactivation of GluA1 homomers and GluA1/2 heteromers and reduces desensitization of GluA1
|
|
GO:0045211
postsynaptic membrane
|
IBA
GO_REF:0000033 |
MODIFY |
Summary: While PRRT1/SynDIG4 is present at synapses as part of AMPAR complexes, recent evidence indicates it is largely intracellular and enriched OUTSIDE the postsynaptic density (PSD). The protein localizes predominantly to endosomal compartments and extrasynaptic AMPAR pools rather than the postsynaptic membrane proper (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Literature shows SynDIG4 is "largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools" (file:human/PRRT1/PRRT1-deep-research-falcon.md). Quantitative colocalization data shows: vGLUT1 15.6%, GluA1 41.2%, transferrin receptor ~20%, EEA1 ~25%, Rab7 <10%, supporting enrichment in early/recycling pathways.
Proposed replacements:
recycling endosome
early endosome
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools. Quantitatively, reported colocalization values in neurons include vGLUT1 15.6%, GluA1 41.2%, transferrin receptor ~20%, EEA1 ~25%, and Rab7 <10%
|
|
GO:0050808
synapse organization
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: PRRT1/SynDIG4 plays a role in synapse organization through its regulation of AMPAR availability at synapses. The protein maintains extrasynaptic AMPAR pools which are necessary for synapse development and function. Knockout of SynDIG4 results in reduced synaptic surface GluA1 and impaired synaptic plasticity (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: UniProt states PRRT1 is "Required to maintain a pool of extrasynaptic AMPA-regulated glutamate receptors which is necessary for synapse development and function" (UniProtKB:Q99946). SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline and impaired LTP/LTD, indicating a role in organizing functional synapses.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline
|
|
GO:0098978
glutamatergic synapse
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: PRRT1/SynDIG4 functions specifically at glutamatergic synapses as an auxiliary subunit of AMPA-type glutamate receptors. All functional studies demonstrate its role in regulating glutamatergic synaptic transmission (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: SynDIG4/PRRT1 is exclusively associated with AMPAR complexes at excitatory glutamatergic synapses. The protein regulates AMPAR trafficking and gating, and SynDIG4 KO specifically affects glutamatergic transmission (LTP/LTD at hippocampal synapses).
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 is an auxiliary protein which regulates trafficking, gating, and synaptic plasticity of AMPA-type receptors
|
|
GO:2000311
regulation of AMPA receptor activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: This is the core biological process annotation for PRRT1/SynDIG4. The protein directly regulates AMPAR activity through multiple mechanisms: modulating gating kinetics, controlling receptor trafficking and recycling, and maintaining surface AMPAR availability (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Extensive evidence supports SynDIG4 as a bona fide AMPAR auxiliary factor. It modulates AMPAR gating (slows deactivation, reduces desensitization), regulates AMPAR endocytic recycling via its YVPV motif, and maintains extrasynaptic/synaptic AMPAR pools through Rab4/Rab11 dynamics. This is the most precise annotation for the core function.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4/PRRT1 functions as an AMPAR auxiliary factor that regulates receptor trafficking, surface/synaptic availability, and gating properties, thereby contributing to basal synaptic transmission and activity-dependent plasticity
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 contains a canonical tyrosine-based endocytic motif, 178-YVPV-181 (YxxPhi), which binds the AP-2 mu2 cargo-sorting subunit
|
|
GO:0005886
plasma membrane
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: PRRT1/SynDIG4 is a transmembrane protein that does localize to the plasma membrane, but this annotation is overly broad. The protein cycles between plasma membrane and endosomal compartments, and is enriched in endosomes and extrasynaptic membrane pools rather than being a constitutive plasma membrane protein (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: While PRRT1 does transit through the plasma membrane as a type II transmembrane protein, its primary functional localization is in endosomal compartments (early endosomes, recycling endosomes) where it regulates AMPAR recycling. The plasma membrane annotation is not wrong but does not capture the primary localization.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
In hippocampal neurons, SynDIG4 localizes partially to early and recycling endosomes and regulates GluA1-containing AMPAR recycling under basal conditions
|
|
GO:0016020
membrane
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: This is a very broad cellular component annotation from InterPro domain mapping. PRRT1 is indeed a membrane protein with a transmembrane domain, so this is technically correct but uninformative.
Reason: PRRT1 contains a transmembrane helix (residues 224-244 per UniProt FT annotation) and is classified as a single-pass type II membrane protein. The IEA annotation from InterPro is technically accurate, if broad. More specific annotations (recycling endosome, early endosome, glutamatergic synapse) provide better localization information.
|
|
GO:0045202
synapse
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: PRRT1/SynDIG4 does localize to synapses as part of the AMPAR complex, but is more accurately described as being enriched at extrasynaptic sites and in endosomal compartments that support synaptic function (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: UniProt subcellular location indicates "Synapse" but literature shows SynDIG4 is "enriched outside the postsynaptic density". While the protein affects synaptic function and synaptic AMPARs, its primary localization is extrasynaptic/endosomal. The broader "synapse" term is acceptable as a general descriptor but not a core localization.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools
|
|
GO:0030545
signaling receptor regulator activity
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Duplicate of the IBA annotation (same GO term). This IEA annotation from Ensembl Compara transfer also supports the role of PRRT1 as an AMPAR regulator (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: This annotation duplicates the IBA annotation for the same term. Both are valid and supported by the literature showing PRRT1 modulates AMPAR gating and activity. Duplicate annotations with different evidence codes are acceptable.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 co-purifies with native AMPAR complexes and modulates gating
|
|
GO:0030672
synaptic vesicle membrane
|
IEA
GO_REF:0000107 |
REMOVE |
Summary: This annotation appears to be incorrect. PRRT1/SynDIG4 is a postsynaptic protein associated with AMPAR complexes and postsynaptic endosomes. There is no evidence for localization to synaptic vesicle membrane, which is a presynaptic structure.
Reason: All functional evidence for SynDIG4/PRRT1 places it at postsynaptic sites as an AMPAR auxiliary subunit. Synaptic vesicles are presynaptic organelles that release neurotransmitters. PRRT1 is not involved in neurotransmitter release or presynaptic function. This appears to be an erroneous orthology transfer - no primary literature supports synaptic vesicle localization.
|
|
GO:0034394
protein localization to cell surface
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: PRRT1/SynDIG4 promotes AMPAR surface expression. UniProt states it "promotes GRIA1 and GRIA2 cell surface expression." This annotation is appropriate as PRRT1 plays a role in localizing these receptor proteins to the cell surface (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: UniProt annotation and literature support that PRRT1 promotes AMPAR surface expression. SynDIG4 regulates GluA1-containing AMPAR recycling which maintains surface receptor pools. KO neurons show "reduced synaptic surface GluA1 at baseline". The process annotation is appropriate.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline, consistent with a deficit in maintaining AMPARs at or near synapses via endosomal recycling
|
|
GO:0060292
long-term synaptic depression
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: PRRT1/SynDIG4 is required for NMDAR-dependent LTD. SynDIG4 KO mice show impaired LTD. This annotation is appropriate as the protein is involved in this form of synaptic plasticity (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Literature shows SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP and show impaired LTD. The involvement in LTD is mechanistically linked to regulation of AMPAR trafficking and recycling dynamics.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP and show impaired LTD
|
|
GO:0098839
postsynaptic density membrane
|
IEA
GO_REF:0000107 |
MODIFY |
Summary: This annotation conflicts with evidence that SynDIG4 is enriched OUTSIDE the postsynaptic density. While some protein may be present in the PSD as part of AMPAR complexes, the primary localization is extrasynaptic and endosomal (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Literature explicitly states SynDIG4 is "enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools". Colocalization with vGLUT1 (a synaptic marker) is only 15.6%. The PSD membrane annotation overstates synaptic enrichment and should be replaced with more accurate endosomal localizations.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools. Quantitatively, reported colocalization values in neurons include vGLUT1 15.6%
|
|
GO:0098978
glutamatergic synapse
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Duplicate of the IBA annotation. PRRT1/SynDIG4 functions at glutamatergic synapses as an AMPAR auxiliary subunit. This is well-supported (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: This annotation duplicates the IBA annotation for glutamatergic synapse. Both are valid and supported by extensive literature showing SynDIG4 specifically regulates AMPAR function at excitatory glutamatergic synapses.
|
|
GO:0006468
protein phosphorylation
|
ISS
GO_REF:0000024 |
REMOVE |
Summary: PRRT1/SynDIG4 is NOT a kinase and does not directly catalyze protein phosphorylation. UniProt states it "Plays a role in regulating basal phosphorylation levels of glutamate receptor GRIA1" - this means it REGULATES phosphorylation indirectly (likely through AMPAR complex dynamics), not that it catalyzes the reaction. PRRT1 has no kinase domain.
Reason: This is an over-annotation. The protein phosphorylation term (GO:0006468) implies direct involvement in the phosphorylation process. PRRT1 lacks any kinase domain and is a single-pass transmembrane protein that functions as an AMPAR auxiliary subunit. Its effect on GRIA1 phosphorylation levels is indirect, mediated through its effects on AMPAR trafficking and complex assembly. Annotation to "regulation of protein phosphorylation" would be more appropriate if needed, but even this may be too specific given the indirect mechanism.
|
|
GO:0034394
protein localization to cell surface
|
ISS
GO_REF:0000024 |
ACCEPT |
Summary: Duplicate of the IEA annotation (same GO term). PRRT1 promotes GRIA1/GRIA2 surface expression through its role in AMPAR recycling (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: This ISS annotation duplicates the IEA annotation and is well-supported by UniProt function description ("promotes GRIA1 and GRIA2 cell surface expression") and literature showing SynDIG4 maintains surface AMPAR pools through endosomal recycling.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline, consistent with a deficit in maintaining AMPARs at or near synapses via endosomal recycling
|
|
GO:0060292
long-term synaptic depression
|
ISS
GO_REF:0000024 |
ACCEPT |
Summary: Duplicate of the IEA annotation. SynDIG4 KO impairs NMDAR-dependent LTD. This annotation is appropriate (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: This ISS annotation duplicates the IEA annotation for LTD involvement. Literature supports that SynDIG4 is required for normal LTD. The mechanism involves regulation of AMPAR recycling dynamics that are required for LTD expression.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP and show impaired LTD
|
|
GO:2000311
regulation of AMPA receptor activity
|
ISS
GO_REF:0000024 |
ACCEPT |
Summary: Duplicate of the IBA annotation. This is the core function of PRRT1/SynDIG4 as an AMPAR auxiliary subunit (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: This ISS annotation duplicates the IBA annotation for AMPAR regulation. This is the most accurate and specific annotation for PRRT1's core function as an AMPAR auxiliary subunit that modulates receptor gating and trafficking.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4/PRRT1 functions as an AMPAR auxiliary factor that regulates receptor trafficking, surface/synaptic availability, and gating properties
|
|
GO:0060291
long-term synaptic potentiation
|
ISS
GO_REF:0000024 |
NEW |
Summary: SynDIG4/PRRT1 is required for single-tetanus-induced LTP. This is a key function that is well-documented but missing from the current annotation set (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Literature clearly shows SynDIG4/PRRT1 is required for single-tetanus-induced LTP and SD4-KO abolishes single-tetanus induced LTP. This is a core function of the protein that should be annotated. The mechanism involves regulation of calcium-permeable AMPAR recruitment and endosomal recycling dynamics.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP
file:human/PRRT1/PRRT1-deep-research-falcon.md
SD4-KO abolishes single-tetanus induced LTP and reduces extrasynaptic GluA1 pools
|
|
GO:0001881
receptor recycling
|
ISS
GO_REF:0000024 |
NEW |
Summary: A core function of SynDIG4/PRRT1 is regulating AMPAR recycling through endosomal compartments. This is a key function missing from current annotations (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Recent literature shows SynDIG4 contains a canonical YxxPhi endocytic motif (YVPV) that binds AP-2 and regulates AMPAR recycling. SynDIG4 KO does not alter baseline endocytosis but reduces recycling of GluA1-containing receptors. This receptor recycling function is central to the protein's role and should be annotated.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
Knockout (KO) does not alter baseline endocytosis but reduces recycling of GluA1-containing receptors, leading to elevated intracellular GluA1/GluA2
file:human/PRRT1/PRRT1-deep-research-falcon.md
SynDIG4 contains a canonical tyrosine-based endocytic motif, 178-YVPV-181 (YxxPhi), which binds the AP-2 mu2 cargo-sorting subunit
|
|
GO:0055037
recycling endosome
|
ISS
GO_REF:0000024 |
NEW |
Summary: SynDIG4/PRRT1 localizes to recycling endosomes where it regulates AMPAR recycling. This is a key localization missing from current annotations (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Reason: Literature shows in hippocampal neurons, SynDIG4 localizes partially to early and recycling endosomes. Colocalization data shows ~20% overlap with transferrin receptor and ~25% with EEA1. SynDIG4 regulates Rab4/Rab11 endosomal dynamics that maintain surface AMPARs.
Supporting Evidence:
file:human/PRRT1/PRRT1-deep-research-falcon.md
In hippocampal neurons, SynDIG4 localizes partially to early and recycling endosomes and regulates GluA1-containing AMPAR recycling under basal conditions
file:human/PRRT1/PRRT1-deep-research-falcon.md
Reported colocalization values in neurons include transferrin receptor ~20%, EEA1 ~25%
|
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template_file: templates/gene_research_go_focused.md
template_variables:
organism: human
gene_id: PRRT1
gene_symbol: PRRT1
uniprot_accession: Q99946
protein_description: 'RecName: Full=Proline-rich transmembrane protein 1; AltName:
Full=Dispanin subfamily D member 1; Short=DSPD1; AltName: Full=Synapse differentiation-induced
protein 4 {ECO:0000250|UniProtKB:O35449}; Short=SynDIG4 {ECO:0000250|UniProtKB:O35449};'
gene_info: Name=PRRT1 {ECO:0000312|HGNC:HGNC:13943}; Synonyms=C6orf31 {ECO:0000312|HGNC:HGNC:13943},
NG5 {ECO:0000250|UniProtKB:Q6MG82};
organism_full: Homo sapiens (Human).
protein_family: Belongs to the CD225/Dispanin family. .
protein_domains: CD225/Dispanin. (IPR051423); CD225/Dispanin_fam. (IPR007593); CD225
(PF04505)
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BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'PRRT1' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene PRRT1 (gene ID: PRRT1, UniProt: Q99946) in human.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Question: You are an expert researcher providing comprehensive, well-cited information.
Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies
Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'PRRT1' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene PRRT1 (gene ID: PRRT1, UniProt: Q99946) in human.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Plan and verification
- Target verification: Human PRRT1 (UniProt Q99946) encodes Proline-rich transmembrane protein 1, also known as Synapse differentiation-induced protein 4 (SynDIG4) and Dispanin subfamily D member 1 (DSPD1). It belongs to the CD225/Dispanin family and is distinct from PRRT2. All evidence cited below refers specifically to SynDIG4/PRRT1 in neurons. (he2025molecularmechanismsof pages 14-19, speca2025functionalcharacterizationof pages 1-2)
Comprehensive research report
1) Key concepts and definitions
- Identity and domain family: PRRT1 encodes SynDIG4/PRRT1, a single-pass, type II transmembrane protein classified within the Dispanin/CD225 family. Type II topology indicates an intracellular N-terminus and an extracellular C-terminus. Recent mechanistic work aligns SynDIG4’s transmembrane helix near the GluA1 M4 helix within AMPA receptor (AMPAR) complexes, positioning SynDIG4 as an auxiliary AMPAR subunit. (he2025molecularmechanismsof pages 14-19, he2025molecularmechanismsof pages 46-52)
- Molecular role at excitatory synapses: SynDIG4/PRRT1 functions as an AMPAR auxiliary factor that regulates receptor trafficking, surface/synaptic availability, and gating properties, thereby contributing to basal synaptic transmission and activity-dependent plasticity (LTP/LTD). (plambeck2023syndig4isan pages 92-102, he2025molecularmechanismsof pages 46-52)
2) Molecular function and mechanism
- AMPAR association and gating: SynDIG4 co-purifies with native AMPAR complexes and modulates gating. Evidence indicates it slows deactivation of GluA1 homomers and GluA1/2 heteromers and reduces desensitization of GluA1, with potential synergy with TARPγ8; a C-terminal hydrophobic segment near AMPAR M4 is important for interaction. (he2025molecularmechanismsof pages 14-19)
- Endocytic sorting signal: SynDIG4 contains a canonical tyrosine-based endocytic motif, 178-YVPV-181 (YxxΦ), which binds the AP‑2 μ2 cargo-sorting subunit; mutating this motif to 178-AVPA-181 disrupts μ2 binding and causes aberrant plasma-membrane accumulation in heterologous cells and primary neurons, indicating a direct role for SynDIG4’s cytoplasmic tail in endocytic trafficking. (Frontiers in Cellular Neuroscience; 23 Jan 2025; https://doi.org/10.3389/fncel.2024.1526034) (speca2025functionalcharacterizationof pages 1-2)
- Endosomal trafficking and recycling: In hippocampal neurons, SynDIG4 localizes partially to early and recycling endosomes and regulates GluA1-containing AMPAR recycling under basal conditions. Knockout (KO) does not alter baseline endocytosis but reduces recycling of GluA1-containing receptors, leading to elevated intracellular GluA1/GluA2 and increased colocalization with Rab4-positive (rapid recycling) endosomes; Rab4–Rab11 overlap is increased and Rab11 endosomes enlarge, consistent with impaired trafficking/fission between Rab4 and Rab11 compartments. (Frontiers in Pharmacology; 21 May 2025; https://doi.org/10.3389/fphar.2025.1568908) (he2025lossofsyndig4prrt1 pages 9-13, he2025lossofsyndig4prrt1 pages 1-2)
3) Subcellular localization
- Extrasynaptic enrichment and endosomes: SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools. Quantitatively, reported colocalization values in neurons include vGLUT1 15.6%, GluA1 41.2%, transferrin receptor ~20%, EEA1 ~25%, and Rab7 <10%, supporting enrichment in early/recycling pathways over late endosomes. (he2025molecularmechanismsof pages 14-19)
- Reduced synaptic surface AMPARs in KO: SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline, consistent with a deficit in maintaining AMPARs at or near synapses via endosomal recycling. (he2025lossofsyndig4prrt1 pages 9-13, he2025lossofsyndig4prrt1 pages 1-2)
4) Role in synaptic plasticity and circuit function
- LTP and LTD: SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP and show impaired LTD while baseline transmission can be relatively intact. This has been linked to regulation of calcium-permeable AMPAR recruitment and endosomal recycling dynamics. (plambeck2023syndig4isan pages 92-102, he2025molecularmechanismsof pages 46-52, he2025lossofsyndig4prrt1 pages 1-2)
- Behavior: SynDIG4 deficiency has been associated with deficits in hippocampal-dependent behaviors such as Morris water maze and novel object recognition, connecting SynDIG4-mediated AMPAR regulation to learning and memory. (he2025molecularmechanismsof pages 14-19)
5) Recent developments and latest research (priority 2023–2024, plus 2025 to capture latest mechanistic advances)
- 2023 doctoral work consolidated SynDIG4’s role as an AMPAR auxiliary subunit, with evidence for bidirectional clustering with GluA1/GluA2 and activity-dependent changes in extrasynaptic vs synaptic distribution; co-expression with GluA1 in oocytes altered AMPAR gating, supporting direct functional modulation. (plambeck2023syndig4isan pages 92-102, plambeck2023syndig4isan pages 1-9)
- 2024–2025 advances defined SynDIG4’s endocytic motif (YVPV) and its AP‑2 μ2 interaction, providing a direct sequence-level mechanism for SynDIG4 internalization and compartment targeting. (Frontiers in Cellular Neuroscience; 23 Jan 2025; https://doi.org/10.3389/fncel.2024.1526034) (speca2025functionalcharacterizationof pages 1-2)
- 2025 cell-biological studies pinpointed SynDIG4’s role in Rab4‑dependent rapid recycling and suggested SynDIG4 modulates Rab4↔Rab11 endosomal dynamics that maintain surface/synaptic AMPARs under basal conditions. (Frontiers in Pharmacology; 21 May 2025; https://doi.org/10.3389/fphar.2025.1568908) (he2025lossofsyndig4prrt1 pages 9-13, he2025lossofsyndig4prrt1 pages 1-2)
6) Current applications and real-world implementations
- Mechanistic framework for AMPAR-targeted interventions: By specifying an AP‑2–dependent endocytic signal and a Rab4→Rab11 recycling checkpoint, recent work positions SynDIG4/PRRT1 as a defined node for modulating extrasynaptic and synaptic AMPAR availability—potentially relevant to disorders of plasticity and cognition where AMPAR trafficking is altered. (speca2025functionalcharacterizationof pages 1-2, he2025lossofsyndig4prrt1 pages 9-13)
7) Expert opinions and analysis
- Converging evidence supports SynDIG4 as a bona fide AMPAR auxiliary factor with a primary role in endosomal sorting/recycling rather than initial biosynthesis or global AMPAR expression. The YxxΦ/AP‑2 interaction explains its internalization dynamics, while Rab4-linked recycling explains reduced synaptic AMPARs and impaired LTP/LTD in KO contexts. Together, these mechanisms are sufficient to account for behavioral phenotypes tied to hippocampal plasticity. (speca2025functionalcharacterizationof pages 1-2, he2025lossofsyndig4prrt1 pages 9-13, he2025molecularmechanismsof pages 46-52)
8) Relevant statistics and data
- Localization (neurons): vGLUT1 15.6%, GluA1 41.2%, transferrin receptor ~20%, EEA1 ~25%, Rab7 <10% (colocalization/overlap). (he2025molecularmechanismsof pages 14-19)
- Recycling assays: Multiple independent dendrite stretches (~40/condition) across 3 biological replicates showed significant decreases in GluA1 recycling and increased Rab4–Rab11 overlap in SynDIG4 KO neurons (p < 0.01 to p < 0.0001). (Frontiers in Pharmacology; 21 May 2025; https://doi.org/10.3389/fphar.2025.1568908) (he2025lossofsyndig4prrt1 pages 9-13)
Gene/protein identification safeguards
- The evidence base consistently uses SynDIG4/PRRT1 (human ortholog) and distinguishes it from PRRT2, which is a different dispanin with separate disease implications. All mechanistic inferences relate to AMPAR trafficking/gating in excitatory neurons. (plambeck2023syndig4isan pages 92-102, speca2025functionalcharacterizationof pages 1-2)
Embedded summary of recent primary sources
| Year | Reference (authors; journal) | Focus / Key findings | Methods / Model | Notable quantitative data | URL / DOI | Citation ID |
|------|-----------------------------|----------------------|-----------------|--------------------------|-----------|-------------|
| 2025 | He C-W & Díaz E.; Frontiers in Pharmacology | SynDIG4/PRRT1 regulates AMPAR recycling via Rab4→Rab11; loss impairs basal recycling, increases GluA1/GluA2 intracellular accumulation, raises Rab4–Rab11 overlap, and reduces synaptic surface GluA1; KO impairs single-tetanus LTP, NMDAR-dependent LTD, and hippocampal-dependent behaviors | Cultured hippocampal neurons, SynDIG4 KO mice, confocal colocalization, recycling assays | ~40 dendrite stretches/condition, 3 biological replicates; significant decreases in GluA1 recycling (reported p-values: p < 0.01, p < 0.001, ***p < 0.0001) | https://doi.org/10.3389/fphar.2025.1568908 | (he2025lossofsyndig4prrt1 pages 9-13) |
| 2025 | Speca DJ et al.; Frontiers in Cellular Neuroscience | Identified canonical YxxΦ endocytic motif (178‑YVPV‑181) in SynDIG4 that binds AP‑2 μ2; mutation (178‑AVPA‑181) disrupts μ2 binding, causes plasma‑membrane accumulation and alters surface co‑localization with GluA2 | Heterologous cells and primary rat hippocampal neurons, site‑directed mutagenesis, co‑localization assays | Mutant 178‑AVPA‑181 induces aberrant PM accumulation vs WT (qualitative; imaging quantification reported in paper) | https://doi.org/10.3389/fncel.2024.1526034 | (speca2025functionalcharacterizationof pages 1-2) |
| 2023 | Plambeck KE; PhD dissertation (UC Davis) | Demonstrated SynDIG4/PRRT1 as an AMPAR auxiliary protein that regulates trafficking, gating, and synaptic plasticity; SD4-KO abolishes single‑tetanus induced LTP and reduces extrasynaptic GluA1 pools | Primary neuronal cultures, Xenopus oocytes (co‑expression), SD4 KO mice, electrophysiology, imaging | Imaging: N = 15 cells/condition for puncta analyses; LTP abolished after single tetanus in KO (qualitative/experimental values reported in dissertation) | N/A (PhD thesis) | (plambeck2023syndig4isan pages 92-102) |
| 2025 | He CW; thesis / monograph (molecular mechanisms chapter) | Reports type II transmembrane topology and TM alignment near GluA1 M4; localization metrics in neurons (extrasynaptic enrichment) and link to PP2B (calcineurin); KO reduces surface GluA1/GluA2 without changing total AMPAR, implicates SynDIG4 in CP‑AMPAR dependent LTP and behavior | Biochemical fractionation, imaging (colocalization), electrophysiology, behavioral assays (Morris water maze, novel object recognition) | Reported localization overlaps: vGLUT1 15.6%, GluA1 41.2%, TfR ~20%, EEA1 ~25%, Rab7 <10%; behavioral deficits noted (qualitative/assay results in thesis) | N/A (Monograph / thesis) | (he2025molecularmechanismsof pages 14-19) |
| 2023 | Plambeck KE; dissertation (intro/results chapter) | Overexpressed SD4 largely intracellular; co‑expression with GluA1 alters gating in oocytes; SD4‑KO shifts extrasynaptic vs synaptic GluA1 distribution (changes in puncta density/area/integrated density) | Imaging of primary neurons, oocyte electrophysiology, KO mouse neuronal analyses | Puncta metrics: N = 15 cells/condition; statistically significant changes in puncta density/area/integrated density reported in chapter | N/A (PhD thesis) | (plambeck2023syndig4isan pages 1-9) |
Table: A concise reference table of recent primary sources (2023–2025) summarizing major findings on human PRRT1/SynDIG4, including its AMPAR‑auxiliary role, endocytic motif, Rab4/Rab11 recycling effects, localization metrics, methods, quantitative notes, and pqac citation IDs for each entry.
Limitations and open questions
- While endocytic and recycling mechanisms are now better defined, quantitative rate constants for specific AMPAR cargo flows through Rab4 vs Rab11 in human neurons remain limited. Additional structural data resolving SynDIG4’s transmembrane contacts with AMPAR M4 in human complexes and in situ dynamics at synapses would refine models of auxiliary subunit cooperation with TARPs/CNIHs/GSG1L. (he2025molecularmechanismsof pages 14-19)
References (with publication details and URLs where available)
- He C‑W and Díaz E. Loss of SynDIG4/PRRT1 alters distribution of AMPA receptors in Rab4- and Rab11-positive endosomes and impairs basal AMPA receptor recycling. Frontiers in Pharmacology. Published 21 May 2025. DOI: 10.3389/fphar.2025.1568908. URL: https://doi.org/10.3389/fphar.2025.1568908 (he2025lossofsyndig4prrt1 pages 9-13, he2025lossofsyndig4prrt1 pages 1-2)
- Speca DJ, He C‑W, Meyer CM, Scott EC, Díaz E. Functional characterization of endocytic signals in the SynDIG/PRRT family members SynDIG1 and SynDIG4 in heterologous cells and neurons. Frontiers in Cellular Neuroscience. Published 23 Jan 2025. DOI: 10.3389/fncel.2024.1526034. URL: https://doi.org/10.3389/fncel.2024.1526034 (speca2025functionalcharacterizationof pages 1-2)
- Plambeck KE. SynDIG4 is an auxiliary protein which regulates trafficking, gating, and synaptic plasticity of AMPA-type receptors. Doctoral dissertation (UC Davis). 2023. (plambeck2023syndig4isan pages 92-102, plambeck2023syndig4isan pages 1-9)
- He CW. Molecular mechanisms of SynDIG4 in regulating AMPA receptor trafficking. Thesis/monograph chapters. 2025. (he2025molecularmechanismsof pages 14-19, he2025molecularmechanismsof pages 46-52)
Citations for major claims in text correspond to context IDs: (he2025molecularmechanismsof pages 14-19, he2025lossofsyndig4prrt1 pages 9-13, he2025molecularmechanismsof pages 68-73, speca2025functionalcharacterizationof pages 1-2, he2025molecularmechanismsof pages 46-52, he2025lossofsyndig4prrt1 pages 1-2, plambeck2023syndig4isan pages 92-102, plambeck2023syndig4isan pages 1-9).
References
(he2025molecularmechanismsof pages 14-19): CW He. Molecular mechanisms of syndig4 in regulating ampa receptor trafficking. Unknown journal, 2025.
(speca2025functionalcharacterizationof pages 1-2): David J. Speca, Chun-Wei He, Christina M. Meyer, Erin C. Scott, and Elva Díaz. Functional characterization of endocytic signals in the syndig/prrt family members syndig1 and syndig4 in heterologous cells and neurons. Frontiers in Cellular Neuroscience, Jan 2025. URL: https://doi.org/10.3389/fncel.2024.1526034, doi:10.3389/fncel.2024.1526034. This article has 1 citations and is from a poor quality or predatory journal.
(he2025molecularmechanismsof pages 46-52): CW He. Molecular mechanisms of syndig4 in regulating ampa receptor trafficking. Unknown journal, 2025.
(plambeck2023syndig4isan pages 92-102): KE Plambeck. Syndig4 is an auxiliary protein which regulates trafficking, gating, and synaptic plasticity of ampa-type receptors. Unknown journal, 2023.
(he2025lossofsyndig4prrt1 pages 9-13): Chun-Wei He and Elva Díaz. Loss of syndig4/prrt1 alters distribution of ampa receptors in rab4- and rab11-positive endosomes and impairs basal ampa receptor recycling. Frontiers in Pharmacology, May 2025. URL: https://doi.org/10.3389/fphar.2025.1568908, doi:10.3389/fphar.2025.1568908. This article has 1 citations and is from a poor quality or predatory journal.
(he2025lossofsyndig4prrt1 pages 1-2): Chun-Wei He and Elva Díaz. Loss of syndig4/prrt1 alters distribution of ampa receptors in rab4- and rab11-positive endosomes and impairs basal ampa receptor recycling. Frontiers in Pharmacology, May 2025. URL: https://doi.org/10.3389/fphar.2025.1568908, doi:10.3389/fphar.2025.1568908. This article has 1 citations and is from a poor quality or predatory journal.
(plambeck2023syndig4isan pages 1-9): KE Plambeck. Syndig4 is an auxiliary protein which regulates trafficking, gating, and synaptic plasticity of ampa-type receptors. Unknown journal, 2023.
(he2025molecularmechanismsof pages 68-73): CW He. Molecular mechanisms of syndig4 in regulating ampa receptor trafficking. Unknown journal, 2025.
id: Q99946
gene_symbol: PRRT1
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
PRRT1 (Proline-rich transmembrane protein 1), also known as SynDIG4 (Synapse
differentiation-induced protein 4), is a single-pass type II transmembrane protein
that functions as an auxiliary subunit of AMPA receptor (AMPAR) complexes. It belongs
to the CD225/Dispanin family. PRRT1 regulates AMPAR trafficking, gating, and synaptic
availability through mechanisms including: (1) direct modulation of AMPAR gating by
slowing deactivation of GluA1 homomers and GluA1/2 heteromers and reducing desensitization;
(2) regulation of AMPAR endocytic recycling via its YxxPhi endocytic motif (YVPV) that
binds the AP-2 mu2 cargo-sorting subunit; and (3) maintaining extrasynaptic AMPAR pools
through Rab4/Rab11-dependent endosomal recycling. Loss of SynDIG4 impairs basal AMPAR
recycling, reduces synaptic surface GluA1, and abolishes single-tetanus-induced LTP
and NMDAR-dependent LTD, leading to deficits in hippocampal-dependent learning and memory.
alternative_products:
- name: '1'
id: Q99946-1
- name: '2'
id: Q99946-2
sequence_note: VSP_003808
existing_annotations:
- term:
id: GO:0030545
label: signaling receptor regulator activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
PRRT1/SynDIG4 directly modulates AMPA receptor (AMPAR) function as an auxiliary
subunit. It binds to AMPAR complexes and regulates their gating properties,
slowing deactivation and reducing desensitization. This constitutes regulation
of a signaling receptor (AMPAR is an ionotropic glutamate receptor). The term
is appropriate as PRRT1 modulates receptor activity rather than acting as the
receptor itself (file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
SynDIG4 functions as an AMPAR auxiliary factor that co-purifies with native
AMPAR complexes and modulates gating (file:human/PRRT1/PRRT1-deep-research-falcon.md).
Evidence shows it slows deactivation of GluA1 homomers and GluA1/2 heteromers
and reduces desensitization of GluA1. IBA annotations have undergone phylogenetic
review and this function is well-supported by the conserved role across orthologs.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 co-purifies with native AMPAR complexes and modulates gating. Evidence indicates it slows deactivation of GluA1 homomers and GluA1/2 heteromers and reduces desensitization of GluA1"
- term:
id: GO:0045211
label: postsynaptic membrane
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
While PRRT1/SynDIG4 is present at synapses as part of AMPAR complexes, recent
evidence indicates it is largely intracellular and enriched OUTSIDE the postsynaptic
density (PSD). The protein localizes predominantly to endosomal compartments and
extrasynaptic AMPAR pools rather than the postsynaptic membrane proper
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: MODIFY
reason: >-
Literature shows SynDIG4 is "largely intracellular and enriched outside the
postsynaptic density, with localization to endosomal compartments and extrasynaptic
AMPAR pools" (file:human/PRRT1/PRRT1-deep-research-falcon.md). Quantitative
colocalization data shows: vGLUT1 15.6%, GluA1 41.2%, transferrin receptor ~20%,
EEA1 ~25%, Rab7 <10%, supporting enrichment in early/recycling pathways.
proposed_replacement_terms:
- id: GO:0055037
label: recycling endosome
- id: GO:0005769
label: early endosome
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools. Quantitatively, reported colocalization values in neurons include vGLUT1 15.6%, GluA1 41.2%, transferrin receptor ~20%, EEA1 ~25%, and Rab7 <10%"
- term:
id: GO:0050808
label: synapse organization
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
PRRT1/SynDIG4 plays a role in synapse organization through its regulation of
AMPAR availability at synapses. The protein maintains extrasynaptic AMPAR pools
which are necessary for synapse development and function. Knockout of SynDIG4
results in reduced synaptic surface GluA1 and impaired synaptic plasticity
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
UniProt states PRRT1 is "Required to maintain a pool of extrasynaptic AMPA-regulated
glutamate receptors which is necessary for synapse development and function"
(UniProtKB:Q99946). SynDIG4 KO neurons show reduced synaptic surface GluA1 at
baseline and impaired LTP/LTD, indicating a role in organizing functional synapses.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline"
- term:
id: GO:0098978
label: glutamatergic synapse
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
PRRT1/SynDIG4 functions specifically at glutamatergic synapses as an auxiliary
subunit of AMPA-type glutamate receptors. All functional studies demonstrate
its role in regulating glutamatergic synaptic transmission
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
SynDIG4/PRRT1 is exclusively associated with AMPAR complexes at excitatory
glutamatergic synapses. The protein regulates AMPAR trafficking and gating,
and SynDIG4 KO specifically affects glutamatergic transmission (LTP/LTD at
hippocampal synapses).
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 is an auxiliary protein which regulates trafficking, gating, and synaptic plasticity of AMPA-type receptors"
- term:
id: GO:2000311
label: regulation of AMPA receptor activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
This is the core biological process annotation for PRRT1/SynDIG4. The protein
directly regulates AMPAR activity through multiple mechanisms: modulating gating
kinetics, controlling receptor trafficking and recycling, and maintaining surface
AMPAR availability (file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
Extensive evidence supports SynDIG4 as a bona fide AMPAR auxiliary factor. It
modulates AMPAR gating (slows deactivation, reduces desensitization), regulates
AMPAR endocytic recycling via its YVPV motif, and maintains extrasynaptic/synaptic
AMPAR pools through Rab4/Rab11 dynamics. This is the most precise annotation
for the core function.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4/PRRT1 functions as an AMPAR auxiliary factor that regulates receptor trafficking, surface/synaptic availability, and gating properties, thereby contributing to basal synaptic transmission and activity-dependent plasticity"
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 contains a canonical tyrosine-based endocytic motif, 178-YVPV-181 (YxxPhi), which binds the AP-2 mu2 cargo-sorting subunit"
- term:
id: GO:0005886
label: plasma membrane
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >-
PRRT1/SynDIG4 is a transmembrane protein that does localize to the plasma membrane,
but this annotation is overly broad. The protein cycles between plasma membrane
and endosomal compartments, and is enriched in endosomes and extrasynaptic membrane
pools rather than being a constitutive plasma membrane protein
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: KEEP_AS_NON_CORE
reason: >-
While PRRT1 does transit through the plasma membrane as a type II transmembrane
protein, its primary functional localization is in endosomal compartments
(early endosomes, recycling endosomes) where it regulates AMPAR recycling.
The plasma membrane annotation is not wrong but does not capture the primary localization.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "In hippocampal neurons, SynDIG4 localizes partially to early and recycling endosomes and regulates GluA1-containing AMPAR recycling under basal conditions"
- term:
id: GO:0016020
label: membrane
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
This is a very broad cellular component annotation from InterPro domain mapping.
PRRT1 is indeed a membrane protein with a transmembrane domain, so this is
technically correct but uninformative.
action: ACCEPT
reason: >-
PRRT1 contains a transmembrane helix (residues 224-244 per UniProt FT annotation)
and is classified as a single-pass type II membrane protein. The IEA annotation
from InterPro is technically accurate, if broad. More specific annotations
(recycling endosome, early endosome, glutamatergic synapse) provide better
localization information.
- term:
id: GO:0045202
label: synapse
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >-
PRRT1/SynDIG4 does localize to synapses as part of the AMPAR complex, but is
more accurately described as being enriched at extrasynaptic sites and in
endosomal compartments that support synaptic function
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: KEEP_AS_NON_CORE
reason: >-
UniProt subcellular location indicates "Synapse" but literature shows SynDIG4
is "enriched outside the postsynaptic density". While the protein affects
synaptic function and synaptic AMPARs, its primary localization is
extrasynaptic/endosomal. The broader "synapse" term is acceptable as a general
descriptor but not a core localization.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools"
- term:
id: GO:0030545
label: signaling receptor regulator activity
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
Duplicate of the IBA annotation (same GO term). This IEA annotation from Ensembl
Compara transfer also supports the role of PRRT1 as an AMPAR regulator
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
This annotation duplicates the IBA annotation for the same term. Both are valid
and supported by the literature showing PRRT1 modulates AMPAR gating and
activity. Duplicate annotations with different evidence codes are acceptable.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 co-purifies with native AMPAR complexes and modulates gating"
- term:
id: GO:0030672
label: synaptic vesicle membrane
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
This annotation appears to be incorrect. PRRT1/SynDIG4 is a postsynaptic protein
associated with AMPAR complexes and postsynaptic endosomes. There is no evidence
for localization to synaptic vesicle membrane, which is a presynaptic structure.
action: REMOVE
reason: >-
All functional evidence for SynDIG4/PRRT1 places it at postsynaptic sites as an
AMPAR auxiliary subunit. Synaptic vesicles are presynaptic organelles that
release neurotransmitters. PRRT1 is not involved in neurotransmitter release
or presynaptic function. This appears to be an erroneous orthology transfer -
no primary literature supports synaptic vesicle localization.
- term:
id: GO:0034394
label: protein localization to cell surface
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
PRRT1/SynDIG4 promotes AMPAR surface expression. UniProt states it "promotes
GRIA1 and GRIA2 cell surface expression." This annotation is appropriate as
PRRT1 plays a role in localizing these receptor proteins to the cell surface
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
UniProt annotation and literature support that PRRT1 promotes AMPAR surface
expression. SynDIG4 regulates GluA1-containing AMPAR recycling which maintains
surface receptor pools. KO neurons show "reduced synaptic surface GluA1 at
baseline". The process annotation is appropriate.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline, consistent with a deficit in maintaining AMPARs at or near synapses via endosomal recycling"
- term:
id: GO:0060292
label: long-term synaptic depression
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
PRRT1/SynDIG4 is required for NMDAR-dependent LTD. SynDIG4 KO mice show impaired
LTD. This annotation is appropriate as the protein is involved in this form of
synaptic plasticity (file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
Literature shows SynDIG4/PRRT1 is required for single-tetanus-induced LTP and
is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP
and show impaired LTD. The involvement in LTD is mechanistically linked to
regulation of AMPAR trafficking and recycling dynamics.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP and show impaired LTD"
- term:
id: GO:0098839
label: postsynaptic density membrane
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
This annotation conflicts with evidence that SynDIG4 is enriched OUTSIDE the
postsynaptic density. While some protein may be present in the PSD as part of
AMPAR complexes, the primary localization is extrasynaptic and endosomal
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: MODIFY
reason: >-
Literature explicitly states SynDIG4 is "enriched outside the postsynaptic
density, with localization to endosomal compartments and extrasynaptic AMPAR
pools". Colocalization with vGLUT1 (a synaptic marker) is only 15.6%. The PSD
membrane annotation overstates synaptic enrichment and should be replaced with
more accurate endosomal localizations.
proposed_replacement_terms:
- id: GO:0055037
label: recycling endosome
- id: GO:0005769
label: early endosome
- id: GO:0098837
label: postsynaptic recycling endosome
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 is largely intracellular and enriched outside the postsynaptic density, with localization to endosomal compartments and extrasynaptic AMPAR pools. Quantitatively, reported colocalization values in neurons include vGLUT1 15.6%"
- term:
id: GO:0098978
label: glutamatergic synapse
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
Duplicate of the IBA annotation. PRRT1/SynDIG4 functions at glutamatergic
synapses as an AMPAR auxiliary subunit. This is well-supported
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
This annotation duplicates the IBA annotation for glutamatergic synapse. Both
are valid and supported by extensive literature showing SynDIG4 specifically
regulates AMPAR function at excitatory glutamatergic synapses.
- term:
id: GO:0006468
label: protein phosphorylation
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
PRRT1/SynDIG4 is NOT a kinase and does not directly catalyze protein
phosphorylation. UniProt states it "Plays a role in regulating basal
phosphorylation levels of glutamate receptor GRIA1" - this means it REGULATES
phosphorylation indirectly (likely through AMPAR complex dynamics), not that
it catalyzes the reaction. PRRT1 has no kinase domain.
action: REMOVE
reason: >-
This is an over-annotation. The protein phosphorylation term (GO:0006468)
implies direct involvement in the phosphorylation process. PRRT1 lacks any
kinase domain and is a single-pass transmembrane protein that functions as an
AMPAR auxiliary subunit. Its effect on GRIA1 phosphorylation levels is indirect,
mediated through its effects on AMPAR trafficking and complex assembly.
Annotation to "regulation of protein phosphorylation" would be more appropriate
if needed, but even this may be too specific given the indirect mechanism.
- term:
id: GO:0034394
label: protein localization to cell surface
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
Duplicate of the IEA annotation (same GO term). PRRT1 promotes GRIA1/GRIA2
surface expression through its role in AMPAR recycling
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
This ISS annotation duplicates the IEA annotation and is well-supported by
UniProt function description ("promotes GRIA1 and GRIA2 cell surface expression")
and literature showing SynDIG4 maintains surface AMPAR pools through endosomal
recycling.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 KO neurons show reduced synaptic surface GluA1 at baseline, consistent with a deficit in maintaining AMPARs at or near synapses via endosomal recycling"
- term:
id: GO:0060292
label: long-term synaptic depression
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
Duplicate of the IEA annotation. SynDIG4 KO impairs NMDAR-dependent LTD.
This annotation is appropriate (file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
This ISS annotation duplicates the IEA annotation for LTD involvement. Literature
supports that SynDIG4 is required for normal LTD. The mechanism involves
regulation of AMPAR recycling dynamics that are required for LTD expression.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP and show impaired LTD"
- term:
id: GO:2000311
label: regulation of AMPA receptor activity
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
Duplicate of the IBA annotation. This is the core function of PRRT1/SynDIG4
as an AMPAR auxiliary subunit (file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: ACCEPT
reason: >-
This ISS annotation duplicates the IBA annotation for AMPAR regulation. This is
the most accurate and specific annotation for PRRT1's core function as an AMPAR
auxiliary subunit that modulates receptor gating and trafficking.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4/PRRT1 functions as an AMPAR auxiliary factor that regulates receptor trafficking, surface/synaptic availability, and gating properties"
# NEW ANNOTATIONS - key functions missing from current annotation set
- term:
id: GO:0060291
label: long-term synaptic potentiation
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
SynDIG4/PRRT1 is required for single-tetanus-induced LTP. This is a key
function that is well-documented but missing from the current annotation set
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: NEW
reason: >-
Literature clearly shows SynDIG4/PRRT1 is required for single-tetanus-induced
LTP and SD4-KO abolishes single-tetanus induced LTP. This is a core function
of the protein that should be annotated. The mechanism involves regulation of
calcium-permeable AMPAR recruitment and endosomal recycling dynamics.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4/PRRT1 is required for single-tetanus-induced LTP and is also implicated in NMDAR-dependent LTD; KO slices lose single-tetanus LTP"
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SD4-KO abolishes single-tetanus induced LTP and reduces extrasynaptic GluA1 pools"
- term:
id: GO:0001881
label: receptor recycling
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
A core function of SynDIG4/PRRT1 is regulating AMPAR recycling through endosomal
compartments. This is a key function missing from current annotations
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: NEW
reason: >-
Recent literature shows SynDIG4 contains a canonical YxxPhi endocytic motif
(YVPV) that binds AP-2 and regulates AMPAR recycling. SynDIG4 KO does not alter
baseline endocytosis but reduces recycling of GluA1-containing receptors. This
receptor recycling function is central to the protein's role and should be annotated.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "Knockout (KO) does not alter baseline endocytosis but reduces recycling of GluA1-containing receptors, leading to elevated intracellular GluA1/GluA2"
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "SynDIG4 contains a canonical tyrosine-based endocytic motif, 178-YVPV-181 (YxxPhi), which binds the AP-2 mu2 cargo-sorting subunit"
- term:
id: GO:0055037
label: recycling endosome
evidence_type: ISS
original_reference_id: GO_REF:0000024
review:
summary: >-
SynDIG4/PRRT1 localizes to recycling endosomes where it regulates AMPAR
recycling. This is a key localization missing from current annotations
(file:human/PRRT1/PRRT1-deep-research-falcon.md).
action: NEW
reason: >-
Literature shows in hippocampal neurons, SynDIG4 localizes partially to early
and recycling endosomes. Colocalization data shows ~20% overlap with transferrin
receptor and ~25% with EEA1. SynDIG4 regulates Rab4/Rab11 endosomal dynamics
that maintain surface AMPARs.
supported_by:
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "In hippocampal neurons, SynDIG4 localizes partially to early and recycling endosomes and regulates GluA1-containing AMPAR recycling under basal conditions"
- reference_id: file:human/PRRT1/PRRT1-deep-research-falcon.md
supporting_text: "Reported colocalization values in neurons include transferrin receptor ~20%, EEA1 ~25%"
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
- id: GO_REF:0000024
title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
by curator judgment of sequence similarity
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied by
UniProt
findings: []
- id: GO_REF:0000107
title: Automatic transfer of experimentally verified manual GO annotation data to
orthologs using Ensembl Compara
findings: []
- id: file:human/PRRT1/PRRT1-deep-research-falcon.md
title: Deep research report on PRRT1/SynDIG4 functional annotation
findings:
- statement: SynDIG4 is a type II transmembrane protein that functions as an AMPAR auxiliary subunit
- statement: Modulates AMPAR gating by slowing deactivation and reducing desensitization
- statement: Localized largely to intracellular and extrasynaptic compartments rather than PSD
- statement: Required for single-tetanus LTP and NMDAR-dependent LTD
- statement: Contains canonical YxxPhi endocytic motif (YVPV) that binds AP-2 mu2
- statement: Regulates AMPAR recycling via Rab4/Rab11 endosomal dynamics
core_functions:
- molecular_function:
id: GO:0030545
label: signaling receptor regulator activity
description: >-
PRRT1/SynDIG4 is an AMPAR auxiliary subunit that directly modulates receptor
gating (slowing deactivation, reducing desensitization) and regulates receptor
trafficking/recycling through its endocytic motif and effects on Rab4/Rab11
endosomal dynamics. Functions as a signaling receptor regulator by binding to
and modulating AMPA receptor activity.
directly_involved_in:
- id: GO:2000311
label: regulation of AMPA receptor activity
- id: GO:0060291
label: long-term synaptic potentiation
- id: GO:0060292
label: long-term synaptic depression
- id: GO:0001881
label: receptor recycling
locations:
- id: GO:0055037
label: recycling endosome
- id: GO:0005769
label: early endosome
- id: GO:0098978
label: glutamatergic synapse