{"gene":"SSR4","run_date":"2026-06-10T07:46:41","timeline":{"discoveries":[{"year":2013,"finding":"SSR4 (signal sequence receptor 4) is a subunit of the heterotetrameric TRAP complex; loss-of-function mutation (c.316delT, p.F106Sfs*53) reduces expression of other TRAP complex proteins and causes underglycosylation, and overexpression of wild-type SSR4 partially restores N-glycosylation. This established that the TRAP complex, which binds to the oligosaccharyltransferase complex, is directly involved in N-glycosylation.","method":"Patient fibroblast analysis, Glyc-ER-GFP glycosylation reporter assay, western blot of TRAP complex members, wild-type SSR4 overexpression rescue","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (reporter assay, western blot, rescue by overexpression) in a single study; foundational mechanistic paper replicated by subsequent clinical reports","pmids":["24218363"],"is_preprint":false},{"year":2015,"finding":"Loss-of-function mutations in SSR4 cause complete loss of SSR4 protein (western blot), confirming SSR4 protein is required for maintaining normal N-glycosylation of serum transferrin.","method":"Western blot analysis of patient-derived samples, whole-exome sequencing","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — western blot confirmation in multiple patients, single lab, two methods (WES + western blot)","pmids":["26264460"],"is_preprint":false},{"year":2024,"finding":"A canonical splicing variant (c.67+2T>C) in SSR4 induces retention of the first 46 bp of intron 1 via recognition of a downstream GC dinucleotide as a non-canonical cryptic donor splice site, generating a premature termination codon that triggers nonsense-mediated mRNA decay and decreases SSR4 expression.","method":"Minigene splicing assay, mRNA sequencing, functional molecular analysis","journal":"Journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — minigene functional assay directly demonstrated aberrant splicing mechanism, single lab","pmids":["39653760"],"is_preprint":false},{"year":2025,"finding":"A splice variant (c.351+1del) in SSR4 produces three abnormal splice forms: 1 bp deletion in 3' end of exon 4, 42 bp deletion in 3' end of exon 4, and skipping of exon 4, all resulting in truncated proteins.","method":"Minigene splicing assay, whole-exome sequencing, Sanger sequencing","journal":"Frontiers in pediatrics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — minigene assay directly demonstrated splice consequences, single lab","pmids":["41210240"],"is_preprint":false},{"year":2026,"finding":"PRRSV non-structural protein Nsp2 physically interacts with SSR4 via its PLP2 and hypervariable domains, selectively upregulates SSR4 expression by prolonging its protein half-life, and SSR4 is required for full activation of PRRSV-induced ER stress (specifically the PERK-eIF2α and IRE1α-XBP1 axes of the UPR), promoting viral replication.","method":"Co-immunoprecipitation (physical interaction), protein half-life assay, functional knockdown studies measuring PRRSV replication and ER stress pathway activation","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction mapped by Co-IP, functional knockdown with defined molecular readouts (UPR pathway activation), single lab","pmids":["42023815"],"is_preprint":false},{"year":2026,"finding":"SSR4 interacts with DDOST (oligosaccharyltransferase subunit) to regulate BAFFR N-glycosylation, thereby sustaining B-cell activation and LTα1β2 expression via NF-κB signaling; B-cell-specific Ssr4 deletion leads to peripheral B-cell loss, reduced antibody output, and increased high-mannose immunoglobulins, while SSR4 overexpression in CHO cells reduces high-mannose glycans and enhances IgG1 ADCC and CDC.","method":"Co-immunoprecipitation (SSR4-DDOST interaction), B-cell-specific conditional knockout mouse model, N-glycan analysis by mass spectrometry, NF-κB signaling readout, antibody functional assays (ADCC, CDC)","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for interaction, conditional KO with defined molecular phenotypes, overexpression with glycan mass spectrometry; single lab but multiple orthogonal methods","pmids":["42159884"],"is_preprint":false},{"year":2025,"finding":"SSR4 regulates expression of NDUFB11 and ATP6AP1, enhancing mitochondrial respiratory chain complex I and complex V function to promote mitochondrial oxidative phosphorylation and gastric cancer progression.","method":"In vitro and in vivo functional studies (cell line knockdown/overexpression), measurement of mitochondrial OXPHOS function, in vivo xenograft models","journal":"Molecular carcinogenesis","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic link between SSR4 and NDUFB11/ATP6AP1 inferred from expression changes rather than direct biochemical interaction; no reconstitution or Co-IP reported in abstract","pmids":["40999562"],"is_preprint":false}],"current_model":"SSR4 (TRAPD) is a subunit of the heterotetrameric TRAP complex in the endoplasmic reticulum membrane where it directly promotes N-linked glycosylation efficiency by associating with the oligosaccharyltransferase complex; loss of SSR4 destabilizes other TRAP subunits and impairs N-glycosylation, and SSR4 additionally interacts with DDOST to regulate specific substrate glycosylation (e.g., BAFFR) with downstream effects on NF-κB signaling, while viral proteins (PRRSV Nsp2) can hijack SSR4 to modulate the unfolded protein response for proviral benefit."},"narrative":{"mechanistic_narrative":"SSR4 is a subunit of the heterotetrameric translocon-associated protein (TRAP) complex in the endoplasmic reticulum membrane, where it supports N-linked glycosylation by acting in concert with the oligosaccharyltransferase complex [PMID:24218363]. Loss-of-function mutations abolish SSR4 protein, destabilize other TRAP subunits, and cause protein underglycosylation, with wild-type SSR4 overexpression restoring N-glycosylation efficiency; these defects underlie a congenital disorder of glycosylation, and multiple pathogenic alleles act through aberrant splicing and nonsense-mediated decay [PMID:24218363, PMID:26264460, PMID:39653760, PMID:41210240]. Beyond bulk glycosylation, SSR4 interacts with the OST subunit DDOST to regulate substrate-specific N-glycosylation: it controls BAFFR glycosylation to sustain B-cell activation and NF-κB-driven LTα1β2 expression, with B-cell-specific deletion causing peripheral B-cell loss, reduced antibody output, and accumulation of high-mannose immunoglobulins [PMID:42159884]. SSR4 is also exploited by viral pathogens: the PRRSV non-structural protein Nsp2 binds SSR4 via its PLP2 and hypervariable domains and stabilizes it, with SSR4 required for full PERK-eIF2α and IRE1α-XBP1 UPR activation that promotes viral replication [PMID:42023815].","teleology":[{"year":2013,"claim":"Established that SSR4 is a functional TRAP complex subunit directly required for N-glycosylation, answering whether the TRAP complex participates in glycosylation rather than acting solely in translocation.","evidence":"Patient fibroblast analysis with Glyc-ER-GFP reporter, western blot of TRAP subunits, and wild-type SSR4 overexpression rescue","pmids":["24218363"],"confidence":"High","gaps":["Direct biochemical contact between SSR4 and the OST complex not structurally resolved","Stoichiometry and architecture of SSR4 within TRAP not defined"]},{"year":2015,"claim":"Confirmed that SSR4 protein loss, not merely reduced expression, drives the glycosylation defect, linking SSR4 deficiency to underglycosylation of serum transferrin in patients.","evidence":"Western blot of patient-derived samples plus whole-exome sequencing","pmids":["26264460"],"confidence":"Medium","gaps":["Single lab; molecular mechanism connecting SSR4 loss to transferrin underglycosylation not dissected","No reconstitution of glycosylation defect in defined system"]},{"year":2024,"claim":"Defined a specific molecular route by which a splicing variant abolishes SSR4, showing intron retention via a cryptic donor site generates a premature stop codon and NMD.","evidence":"Minigene splicing assay and mRNA sequencing","pmids":["39653760"],"confidence":"Medium","gaps":["Single lab; downstream glycosylation consequence inferred rather than measured","Generalizability to other SSR4 alleles unaddressed"]},{"year":2025,"claim":"Extended the spectrum of disease-causing SSR4 splice defects by showing a single deletion produces multiple aberrant exon-4 splice forms yielding truncated proteins.","evidence":"Minigene splicing assay, whole-exome and Sanger sequencing","pmids":["41210240"],"confidence":"Medium","gaps":["Single lab; functional impact of truncated proteins on glycosylation not quantified","Relative abundance of the three splice forms in patient tissue unknown"]},{"year":2026,"claim":"Moved SSR4 from a general glycosylation factor to a substrate-specific regulator by showing it acts via DDOST to control BAFFR glycosylation and sustain B-cell activation and NF-κB signaling.","evidence":"Co-IP of SSR4-DDOST, B-cell-specific conditional knockout mouse, N-glycan mass spectrometry, NF-κB readouts, and ADCC/CDC antibody assays","pmids":["42159884"],"confidence":"Medium","gaps":["Single lab; whether BAFFR is a direct vs indirect SSR4 substrate not established","Breadth of SSR4 substrate selectivity beyond BAFFR/immunoglobulins unknown"]},{"year":2026,"claim":"Identified SSR4 as a target hijacked by a viral protein, showing PRRSV Nsp2 binds and stabilizes SSR4 to drive UPR-dependent proviral ER stress.","evidence":"Co-immunoprecipitation with domain mapping, protein half-life assay, and knockdown measuring PRRSV replication and UPR pathway activation","pmids":["42023815"],"confidence":"Medium","gaps":["Single lab; mechanism by which SSR4 promotes PERK and IRE1α activation not defined","Whether SSR4 acts through TRAP/OST in this UPR role unaddressed"]},{"year":null,"claim":"How SSR4 confers substrate selectivity within TRAP/OST and how its glycosylation role connects to reported metabolic and oncogenic phenotypes remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of SSR4 within the TRAP-OST assembly","Mechanistic basis for SSR4-dependent regulation of NDUFB11/ATP6AP1 and OXPHOS not established by direct interaction data"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,5]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,5]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[4]}],"complexes":["TRAP complex"],"partners":["DDOST","NSP2 (PRRSV)"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P51571","full_name":"Translocon-associated protein subunit delta","aliases":["Signal sequence receptor subunit delta","SSR-delta"],"length_aa":173,"mass_kda":19.0,"function":"TRAP proteins are part of a complex whose function is to bind calcium to the ER membrane and thereby regulate the retention of ER resident proteins","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/P51571/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SSR4","classification":"Not Classified","n_dependent_lines":17,"n_total_lines":1208,"dependency_fraction":0.014072847682119206},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CANX","stoichiometry":4.0},{"gene":"DDOST","stoichiometry":4.0},{"gene":"NPM3","stoichiometry":4.0},{"gene":"RPL19","stoichiometry":4.0},{"gene":"RPL4","stoichiometry":4.0},{"gene":"RPS16","stoichiometry":4.0},{"gene":"SRP68","stoichiometry":4.0},{"gene":"BCAP31","stoichiometry":0.2},{"gene":"CAPRIN1","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SSR4","total_profiled":1310},"omim":[{"mim_id":"610384","title":"HECT, C2, AND WW DOMAINS-CONTAINING E3 UBIQUITIN-PROTEIN LIGASE 1; HECW1","url":"https://www.omim.org/entry/610384"},{"mim_id":"606213","title":"SIGNAL SEQUENCE RECEPTOR, GAMMA; SSR3","url":"https://www.omim.org/entry/606213"},{"mim_id":"300934","title":"CONGENITAL DISORDER OF GLYCOSYLATION, TYPE Iy; CDG1Y","url":"https://www.omim.org/entry/300934"},{"mim_id":"300090","title":"SIGNAL SEQUENCE RECEPTOR, DELTA; SSR4","url":"https://www.omim.org/entry/300090"},{"mim_id":"147450","title":"SUPEROXIDE DISMUTASE 1; SOD1","url":"https://www.omim.org/entry/147450"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Endoplasmic reticulum","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"pancreas","ntpm":2940.4}],"url":"https://www.proteinatlas.org/search/SSR4"},"hgnc":{"alias_symbol":["TRAPD"],"prev_symbol":[]},"alphafold":{"accession":"P51571","domains":[{"cath_id":"2.60.40","chopping":"22-142","consensus_level":"medium","plddt":90.4111,"start":22,"end":142},{"cath_id":"1.20.5","chopping":"144-173","consensus_level":"medium","plddt":92.348,"start":144,"end":173}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P51571","model_url":"https://alphafold.ebi.ac.uk/files/AF-P51571-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P51571-F1-predicted_aligned_error_v6.png","plddt_mean":88.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SSR4","jax_strain_url":"https://www.jax.org/strain/search?query=SSR4"},"sequence":{"accession":"P51571","fasta_url":"https://rest.uniprot.org/uniprotkb/P51571.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P51571/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P51571"}},"corpus_meta":[{"pmid":"24218363","id":"PMC_24218363","title":"A new congenital disorder of glycosylation caused by a mutation in SSR4, the signal sequence receptor 4 protein of the TRAP complex.","date":"2013","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24218363","citation_count":52,"is_preprint":false},{"pmid":"26264460","id":"PMC_26264460","title":"Expanding the Molecular and Clinical Phenotype of SSR4-CDG.","date":"2015","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/26264460","citation_count":28,"is_preprint":false},{"pmid":"32317391","id":"PMC_32317391","title":"Nuclear Ssr4 Is Required for the In Vitro and In Vivo Asexual Cycles and Global Gene Activity of Beauveria bassiana.","date":"2020","source":"mSystems","url":"https://pubmed.ncbi.nlm.nih.gov/32317391","citation_count":21,"is_preprint":false},{"pmid":"38805916","id":"PMC_38805916","title":"SSR4-CDG, an ultra-rare X-linked congenital disorder of glycosylation affecting the TRAP complex: Review of 22 affected individuals including the first adult patient.","date":"2024","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/38805916","citation_count":16,"is_preprint":false},{"pmid":"33300232","id":"PMC_33300232","title":"Expanding the phenotype of X-linked SSR4-CDG: Connective tissue implications.","date":"2020","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/33300232","citation_count":14,"is_preprint":false},{"pmid":"36386804","id":"PMC_36386804","title":"Case Report: The novel hemizygous mutation in the SSR4 gene caused congenital disorder of glycosylation type iy: A case study and literature review.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/36386804","citation_count":7,"is_preprint":false},{"pmid":"39086474","id":"PMC_39086474","title":"A novel SSR4 variant associated with congenital disorder of glycosylation: a case report and related analysis.","date":"2024","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39086474","citation_count":5,"is_preprint":false},{"pmid":"36854416","id":"PMC_36854416","title":"[A case of Congenital disorder of glycosylation due to SSR4 gene deletion].","date":"2023","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/36854416","citation_count":4,"is_preprint":false},{"pmid":"40066443","id":"PMC_40066443","title":"Unveiling SSR4: a promising biomarker in esophageal squamous cell carcinoma.","date":"2025","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/40066443","citation_count":3,"is_preprint":false},{"pmid":"33263569","id":"PMC_33263569","title":"The X-ray crystal structure of the N-terminal domain of Ssr4, a Schizosaccharomyces pombe chromatin-remodelling protein.","date":"2020","source":"Acta crystallographica. Section F, Structural biology communications","url":"https://pubmed.ncbi.nlm.nih.gov/33263569","citation_count":3,"is_preprint":false},{"pmid":"15057039","id":"PMC_15057039","title":"Cloning and molecular characterization of a human ortholog of Monodelphis TRAPD in ultraviolet B-induced melanoma.","date":"2004","source":"Melanoma research","url":"https://pubmed.ncbi.nlm.nih.gov/15057039","citation_count":2,"is_preprint":false},{"pmid":"35810430","id":"PMC_35810430","title":"[Analysis of SSR4 gene variant in a child with congenital glycosylation type 1y in conjunct with congenital dysplasia of external auditory canal].","date":"2022","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35810430","citation_count":2,"is_preprint":false},{"pmid":"39653760","id":"PMC_39653760","title":"Intron retention caused by a canonical splicing variant in SSR4-related congenital disorder of glycosylation.","date":"2024","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39653760","citation_count":2,"is_preprint":false},{"pmid":"40999562","id":"PMC_40999562","title":"SSR4 Promote Gastric Cancer Progression by Regulating Mitochondrial Oxidative Phosphorylation via NDUFB11 and ATP6AP1.","date":"2025","source":"Molecular carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/40999562","citation_count":1,"is_preprint":false},{"pmid":"41210240","id":"PMC_41210240","title":"Novel SSR4 gene splice variant leads to congenital disorder of glycosylation, type Iy.","date":"2025","source":"Frontiers in pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/41210240","citation_count":1,"is_preprint":false},{"pmid":"17268179","id":"PMC_17268179","title":"Rat gene mapping in the post-genome sequencing era: the continued utility of cell hybrids to localize rat genes (Cks2, Ephb4, Fabp5, Il13ra1, Rpl10, Ssr4).","date":"2007","source":"Cytogenetic and genome research","url":"https://pubmed.ncbi.nlm.nih.gov/17268179","citation_count":1,"is_preprint":false},{"pmid":"40662097","id":"PMC_40662097","title":"Hemizygous contiguous gene deletion within Xq28 that includes BCAP31, ABCD1, SRPK3 and SSR4: case report and literature review.","date":"2025","source":"Global medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40662097","citation_count":1,"is_preprint":false},{"pmid":"41649879","id":"PMC_41649879","title":"The TRAP complex (SSR1-SSR4): mechanistic roles and therapeutic opportunities.","date":"2026","source":"Annals of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41649879","citation_count":0,"is_preprint":false},{"pmid":"42023815","id":"PMC_42023815","title":"The host protein SSR4 mediates PRRSV-induced endoplasmic reticulum stress via interaction with Nsp2.","date":"2026","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/42023815","citation_count":0,"is_preprint":false},{"pmid":"41441028","id":"PMC_41441028","title":"Multi-Omics Characterization of a Novel SSR4 Variant in Congenital Disorders of Glycosylation.","date":"2025","source":"Metabolites","url":"https://pubmed.ncbi.nlm.nih.gov/41441028","citation_count":0,"is_preprint":false},{"pmid":"42159884","id":"PMC_42159884","title":"SSR4 sustains Tertiary Lymphoid Structures by Regulation Quality Control of N-linked Glycosylation During B-cell Differentiation Into Plasmacyte in Colorectal Cancer.","date":"2026","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/42159884","citation_count":0,"is_preprint":false},{"pmid":"41960028","id":"PMC_41960028","title":"Early neonatal diagnosis of SSR4-related congenital disorder of glycosylation with severe congenital heart defects: a case report and systematic review.","date":"2026","source":"Frontiers in pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/41960028","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.01.25332712","title":"Experiences of contraceptive use and contraceptive counseling among German psychology students: a cross-sectional online survey","date":"2025-08-05","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.01.25332712","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13187,"output_tokens":1840,"usd":0.03358,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8740,"output_tokens":2452,"usd":0.0525,"stage2_stop_reason":"end_turn"},"total_usd":0.08608,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"SSR4 (signal sequence receptor 4) is a subunit of the heterotetrameric TRAP complex; loss-of-function mutation (c.316delT, p.F106Sfs*53) reduces expression of other TRAP complex proteins and causes underglycosylation, and overexpression of wild-type SSR4 partially restores N-glycosylation. This established that the TRAP complex, which binds to the oligosaccharyltransferase complex, is directly involved in N-glycosylation.\",\n      \"method\": \"Patient fibroblast analysis, Glyc-ER-GFP glycosylation reporter assay, western blot of TRAP complex members, wild-type SSR4 overexpression rescue\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (reporter assay, western blot, rescue by overexpression) in a single study; foundational mechanistic paper replicated by subsequent clinical reports\",\n      \"pmids\": [\"24218363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Loss-of-function mutations in SSR4 cause complete loss of SSR4 protein (western blot), confirming SSR4 protein is required for maintaining normal N-glycosylation of serum transferrin.\",\n      \"method\": \"Western blot analysis of patient-derived samples, whole-exome sequencing\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — western blot confirmation in multiple patients, single lab, two methods (WES + western blot)\",\n      \"pmids\": [\"26264460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A canonical splicing variant (c.67+2T>C) in SSR4 induces retention of the first 46 bp of intron 1 via recognition of a downstream GC dinucleotide as a non-canonical cryptic donor splice site, generating a premature termination codon that triggers nonsense-mediated mRNA decay and decreases SSR4 expression.\",\n      \"method\": \"Minigene splicing assay, mRNA sequencing, functional molecular analysis\",\n      \"journal\": \"Journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — minigene functional assay directly demonstrated aberrant splicing mechanism, single lab\",\n      \"pmids\": [\"39653760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A splice variant (c.351+1del) in SSR4 produces three abnormal splice forms: 1 bp deletion in 3' end of exon 4, 42 bp deletion in 3' end of exon 4, and skipping of exon 4, all resulting in truncated proteins.\",\n      \"method\": \"Minigene splicing assay, whole-exome sequencing, Sanger sequencing\",\n      \"journal\": \"Frontiers in pediatrics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — minigene assay directly demonstrated splice consequences, single lab\",\n      \"pmids\": [\"41210240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PRRSV non-structural protein Nsp2 physically interacts with SSR4 via its PLP2 and hypervariable domains, selectively upregulates SSR4 expression by prolonging its protein half-life, and SSR4 is required for full activation of PRRSV-induced ER stress (specifically the PERK-eIF2α and IRE1α-XBP1 axes of the UPR), promoting viral replication.\",\n      \"method\": \"Co-immunoprecipitation (physical interaction), protein half-life assay, functional knockdown studies measuring PRRSV replication and ER stress pathway activation\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction mapped by Co-IP, functional knockdown with defined molecular readouts (UPR pathway activation), single lab\",\n      \"pmids\": [\"42023815\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SSR4 interacts with DDOST (oligosaccharyltransferase subunit) to regulate BAFFR N-glycosylation, thereby sustaining B-cell activation and LTα1β2 expression via NF-κB signaling; B-cell-specific Ssr4 deletion leads to peripheral B-cell loss, reduced antibody output, and increased high-mannose immunoglobulins, while SSR4 overexpression in CHO cells reduces high-mannose glycans and enhances IgG1 ADCC and CDC.\",\n      \"method\": \"Co-immunoprecipitation (SSR4-DDOST interaction), B-cell-specific conditional knockout mouse model, N-glycan analysis by mass spectrometry, NF-κB signaling readout, antibody functional assays (ADCC, CDC)\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for interaction, conditional KO with defined molecular phenotypes, overexpression with glycan mass spectrometry; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"42159884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SSR4 regulates expression of NDUFB11 and ATP6AP1, enhancing mitochondrial respiratory chain complex I and complex V function to promote mitochondrial oxidative phosphorylation and gastric cancer progression.\",\n      \"method\": \"In vitro and in vivo functional studies (cell line knockdown/overexpression), measurement of mitochondrial OXPHOS function, in vivo xenograft models\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic link between SSR4 and NDUFB11/ATP6AP1 inferred from expression changes rather than direct biochemical interaction; no reconstitution or Co-IP reported in abstract\",\n      \"pmids\": [\"40999562\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SSR4 (TRAPD) is a subunit of the heterotetrameric TRAP complex in the endoplasmic reticulum membrane where it directly promotes N-linked glycosylation efficiency by associating with the oligosaccharyltransferase complex; loss of SSR4 destabilizes other TRAP subunits and impairs N-glycosylation, and SSR4 additionally interacts with DDOST to regulate specific substrate glycosylation (e.g., BAFFR) with downstream effects on NF-κB signaling, while viral proteins (PRRSV Nsp2) can hijack SSR4 to modulate the unfolded protein response for proviral benefit.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SSR4 is a subunit of the heterotetrameric translocon-associated protein (TRAP) complex in the endoplasmic reticulum membrane, where it supports N-linked glycosylation by acting in concert with the oligosaccharyltransferase complex [#0]. Loss-of-function mutations abolish SSR4 protein, destabilize other TRAP subunits, and cause protein underglycosylation, with wild-type SSR4 overexpression restoring N-glycosylation efficiency; these defects underlie a congenital disorder of glycosylation, and multiple pathogenic alleles act through aberrant splicing and nonsense-mediated decay [#0, #1, #2, #3]. Beyond bulk glycosylation, SSR4 interacts with the OST subunit DDOST to regulate substrate-specific N-glycosylation: it controls BAFFR glycosylation to sustain B-cell activation and NF-\\u03baB-driven LT\\u03b11\\u03b22 expression, with B-cell-specific deletion causing peripheral B-cell loss, reduced antibody output, and accumulation of high-mannose immunoglobulins [#5]. SSR4 is also exploited by viral pathogens: the PRRSV non-structural protein Nsp2 binds SSR4 via its PLP2 and hypervariable domains and stabilizes it, with SSR4 required for full PERK-eIF2\\u03b1 and IRE1\\u03b1-XBP1 UPR activation that promotes viral replication [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established that SSR4 is a functional TRAP complex subunit directly required for N-glycosylation, answering whether the TRAP complex participates in glycosylation rather than acting solely in translocation.\",\n      \"evidence\": \"Patient fibroblast analysis with Glyc-ER-GFP reporter, western blot of TRAP subunits, and wild-type SSR4 overexpression rescue\",\n      \"pmids\": [\"24218363\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Direct biochemical contact between SSR4 and the OST complex not structurally resolved\",\n        \"Stoichiometry and architecture of SSR4 within TRAP not defined\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Confirmed that SSR4 protein loss, not merely reduced expression, drives the glycosylation defect, linking SSR4 deficiency to underglycosylation of serum transferrin in patients.\",\n      \"evidence\": \"Western blot of patient-derived samples plus whole-exome sequencing\",\n      \"pmids\": [\"26264460\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab; molecular mechanism connecting SSR4 loss to transferrin underglycosylation not dissected\",\n        \"No reconstitution of glycosylation defect in defined system\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined a specific molecular route by which a splicing variant abolishes SSR4, showing intron retention via a cryptic donor site generates a premature stop codon and NMD.\",\n      \"evidence\": \"Minigene splicing assay and mRNA sequencing\",\n      \"pmids\": [\"39653760\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab; downstream glycosylation consequence inferred rather than measured\",\n        \"Generalizability to other SSR4 alleles unaddressed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended the spectrum of disease-causing SSR4 splice defects by showing a single deletion produces multiple aberrant exon-4 splice forms yielding truncated proteins.\",\n      \"evidence\": \"Minigene splicing assay, whole-exome and Sanger sequencing\",\n      \"pmids\": [\"41210240\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab; functional impact of truncated proteins on glycosylation not quantified\",\n        \"Relative abundance of the three splice forms in patient tissue unknown\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Moved SSR4 from a general glycosylation factor to a substrate-specific regulator by showing it acts via DDOST to control BAFFR glycosylation and sustain B-cell activation and NF-\\u03baB signaling.\",\n      \"evidence\": \"Co-IP of SSR4-DDOST, B-cell-specific conditional knockout mouse, N-glycan mass spectrometry, NF-\\u03baB readouts, and ADCC/CDC antibody assays\",\n      \"pmids\": [\"42159884\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab; whether BAFFR is a direct vs indirect SSR4 substrate not established\",\n        \"Breadth of SSR4 substrate selectivity beyond BAFFR/immunoglobulins unknown\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified SSR4 as a target hijacked by a viral protein, showing PRRSV Nsp2 binds and stabilizes SSR4 to drive UPR-dependent proviral ER stress.\",\n      \"evidence\": \"Co-immunoprecipitation with domain mapping, protein half-life assay, and knockdown measuring PRRSV replication and UPR pathway activation\",\n      \"pmids\": [\"42023815\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single lab; mechanism by which SSR4 promotes PERK and IRE1\\u03b1 activation not defined\",\n        \"Whether SSR4 acts through TRAP/OST in this UPR role unaddressed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SSR4 confers substrate selectivity within TRAP/OST and how its glycosylation role connects to reported metabolic and oncogenic phenotypes remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of SSR4 within the TRAP-OST assembly\",\n        \"Mechanistic basis for SSR4-dependent regulation of NDUFB11/ATP6AP1 and OXPHOS not established by direct interaction data\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"TRAP complex\"],\n    \"partners\": [\"DDOST\", \"Nsp2 (PRRSV)\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}