{"gene":"TXNDC15","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2024,"finding":"TMX5/TXNDC15 covalently engages, via its active-site cysteine residue at position 220, a subset of secretory proteins—mainly single- and multipass Golgi-resident polypeptides—indicating it acts as a natural trapping mutant within the PDI family.","method":"Biochemical trapping/co-immunoprecipitation with active-site cysteine mutants; identification of covalently associated substrate proteins","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal covalent trapping with active-site mutagenesis, single lab, multiple substrate classes identified","pmids":["39348940"],"is_preprint":false},{"year":2024,"finding":"TMX5/TXNDC15 interacts non-covalently and covalently (via non-catalytic cysteine residues) with PDI family members PDI, ERp57, and ERp44. The association with ERp44 requires a mixed disulfide between the catalytic cysteine 29 of ERp44 and the non-catalytic cysteines 114 and/or 124 of TMX5, and this interaction controls the ER/pre-Golgi localization of TMX5.","method":"Co-immunoprecipitation, cysteine mutagenesis (active-site and non-catalytic residues), subcellular localization assays","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-specific mutagenesis identifying precise cysteines, co-IP validation, single lab","pmids":["39348940"],"is_preprint":false},{"year":2024,"finding":"TMX5/TXNDC15 lacks its own ER localization/retention sequence and relies on ERp44 engagement for proper intercompartmental (pre-Golgi) distribution, placing it in the same class as Ero1α, Ero1β, Prx4, ERAP1, and SUMF1.","method":"Subcellular localization experiments combined with cysteine mutagenesis abolishing ERp44 interaction; fractionation/immunofluorescence","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — localization tied functionally to specific interaction, single lab, orthogonal methods","pmids":["39348940"],"is_preprint":false},{"year":2024,"finding":"TXNDC15-knockout cells exhibit defects in MKS (transition zone) module assembly and in ciliary membrane protein localization. Rescue experiments showed that exogenous expression of TXNDC15 constructs harboring MKS-associated variants in the thioredoxin domain failed to rescue these defects, and mutation of two cysteine residues within the thioredoxin domain also failed to rescue, indicating TXNDC15 controls transition zone integrity from outside the TZ via its thioredoxin domain.","method":"TXNDC15 knockout cell lines, rescue with wild-type and mutant constructs (disease-variant and cysteine mutants), immunofluorescence of TZ components and ciliary membrane proteins","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined cellular phenotype, multiple rescue constructs, cysteine mutagenesis, single lab","pmids":["39679447"],"is_preprint":false},{"year":2026,"finding":"TXNDC15 is an essential factor in MARCHF6-mediated ER-associated protein degradation (ERAD). Loss of TXNDC15 impairs substrate (ABHD2) exit and degradation from the ER; this function is catalysis-independent. Loss of TXNDC15 also remodels the ER proteome and lipid homeostasis.","method":"Genome-wide CRISPR-based functional screen for ERAD substrates, TXNDC15 KO validation, proteomic analysis of ER proteome and lipidomics, catalytic mutant rescue experiments","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen plus KO validation with proteomic and lipidomic readouts, catalysis-independent mechanism established by mutant rescue, preprint single lab","pmids":["41959069"],"is_preprint":true},{"year":2026,"finding":"A CRISPR-Cas9 mouse model homozygous for the frameshift variant Txndc15 c.512delA (equivalent to human c.560delA) exhibits the complete Meckel-Gruber syndrome phenotype at embryonic day 15.5, including fetal lethality, exencephaly, omphalocele, postaxial polydactyly, and polycystic kidneys, with markedly reduced TXNDC15 protein in brain, liver, and kidney, confirming TXNDC15 as a bona fide MKS disease gene.","method":"CRISPR-Cas9 knock-in mouse model; embryo phenotyping at E15.5; Western blot for TXNDC15 protein levels in tissues","journal":"Genesis (New York, N.Y. : 2000)","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vivo genetic model with complete phenotype recapitulation and protein-level validation, confirms causality of specific variant","pmids":["41518077"],"is_preprint":false},{"year":2026,"finding":"TXNDC15 interacts with the mitotic kinase NEK4 and suppresses lung adenocarcinoma cell proliferation by inducing G2/M phase arrest, placing TXNDC15 as an upstream regulator of NEK4-dependent G2/M checkpoint control.","method":"Co-immunoprecipitation (TXNDC15–NEK4 interaction), loss-of-function assays, cell cycle analysis (G2/M arrest readout)","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP and functional assay, single lab, no structural or mutagenesis confirmation of interaction interface","pmids":["42214920"],"is_preprint":false}],"current_model":"TXNDC15/TMX5 is an ER-resident thioredoxin-related transmembrane PDI family member that lacks autonomous ER retention signals and relies on ERp44 engagement (via non-catalytic cysteines 114/124) for pre-Golgi localization; it covalently traps Golgi-resident substrates via its active-site cysteine C220 and supports MARCHF6-mediated ERAD through a catalysis-independent mechanism; in cilia biology, its thioredoxin domain is required—from outside the transition zone—for MKS module assembly and ciliary membrane protein gating, and loss of the gene in mice fully recapitulates Meckel-Gruber syndrome."},"narrative":{"mechanistic_narrative":"TXNDC15 (TMX5) is an ER-resident thioredoxin-related transmembrane member of the protein disulfide isomerase (PDI) family that links redox-dependent disulfide chemistry to protein quality control, secretory trafficking, and ciliary signaling [PMID:39348940]. It functions as a natural \"trapping mutant\" within the PDI family, using its active-site cysteine C220 to covalently engage a subset of single- and multipass Golgi-resident secretory proteins [PMID:39348940]. TXNDC15 lacks its own ER retention signal and instead achieves its ER/pre-Golgi localization through engagement of ERp44, a mixed disulfide forming between the catalytic cysteine of ERp44 and the non-catalytic cysteines C114/C124 of TXNDC15; it also associates with PDI and ERp57 [PMID:39348940]. Beyond substrate trapping, TXNDC15 is an essential, catalysis-independent factor in MARCHF6-mediated ER-associated degradation, where its loss impairs substrate (ABHD2) exit and degradation and remodels the ER proteome and lipid homeostasis [PMID:41959069]. In cilia biology, its thioredoxin domain is required—acting from outside the transition zone—for assembly of the MKS module and proper gating of ciliary membrane proteins, with both disease-associated thioredoxin-domain variants and cysteine mutations failing to rescue knockout defects [PMID:39679447]. A frameshift knock-in mouse fully recapitulates Meckel-Gruber syndrome, establishing TXNDC15 as a bona fide MKS disease gene [PMID:41518077].","teleology":[{"year":2024,"claim":"Defining how an active-site PDI-family cysteine engages secretory cargo answered whether TXNDC15 acts catalytically or as a trap, establishing it as a covalent substrate-capturing oxidoreductase.","evidence":"Biochemical covalent trapping and co-IP with active-site cysteine mutants identifying Golgi-resident substrates","pmids":["39348940"],"confidence":"Medium","gaps":["Substrate release/turnover mechanism not resolved","Physiological consequence of trapping individual substrates not established","Single lab"]},{"year":2024,"claim":"Mapping the precise cysteines mediating ERp44 binding answered how a retention-signal-less protein is localized, showing TXNDC15 distribution is enforced by a mixed-disulfide handoff rather than an intrinsic motif.","evidence":"Co-IP plus active-site and non-catalytic cysteine mutagenesis and subcellular localization assays","pmids":["39348940"],"confidence":"Medium","gaps":["Dynamics of ERp44 cycling not characterized","Whether PDI/ERp57 associations are functional or incidental unclear","Single lab"]},{"year":2024,"claim":"Linking TXNDC15 thioredoxin-domain integrity to transition-zone assembly answered how a disease gene contributes to ciliogenesis, showing it controls MKS module assembly and ciliary membrane gating remotely via redox-relevant cysteines.","evidence":"Knockout cells with wild-type, disease-variant, and cysteine-mutant rescue and immunofluorescence of TZ and ciliary membrane components","pmids":["39679447"],"confidence":"Medium","gaps":["Direct ciliary substrate(s) of TXNDC15 not identified","Mechanism connecting ER-located activity to transition-zone integrity unresolved","Single lab"]},{"year":2026,"claim":"Identifying TXNDC15 as essential for MARCHF6-dependent ERAD answered whether its quality-control role requires catalysis, showing a catalysis-independent function in substrate exit and degradation that also shapes ER lipid homeostasis.","evidence":"Genome-wide CRISPR screen, KO validation, catalytic mutant rescue, ER proteomics and lipidomics (preprint)","pmids":["41959069"],"confidence":"Medium","gaps":["Molecular basis of catalysis-independent ERAD support unknown","Whether TXNDC15 directly contacts MARCHF6 not shown","Preprint, single lab"]},{"year":2026,"claim":"An in vivo frameshift model answered whether loss of TXNDC15 is causal for Meckel-Gruber syndrome, confirming complete phenotype recapitulation and disease-gene status.","evidence":"CRISPR-Cas9 knock-in mouse, E15.5 embryo phenotyping, tissue Western blot for TXNDC15","pmids":["41518077"],"confidence":"High","gaps":["Cell-type-specific contribution to each malformation not dissected","Link between molecular redox/ERAD function and organ phenotypes not mechanistically traced"]},{"year":2026,"claim":"A reported TXNDC15-NEK4 interaction raised a potential cell-cycle/tumor-suppressive role, implicating TXNDC15 in G2/M checkpoint control in lung adenocarcinoma.","evidence":"Co-IP and loss-of-function cell cycle analysis","pmids":["42214920"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation or interaction-interface mapping","No structural or mutagenesis confirmation","Mechanism linking an ER oxidoreductase to mitotic NEK4 unexplained"]},{"year":null,"claim":"How TXNDC15's ER redox/ERAD activities mechanistically produce its ciliary transition-zone and developmental functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying mechanism connecting ER-localized disulfide chemistry to transition-zone assembly","Direct ciliary and ERAD substrates incompletely defined","Structural basis of substrate/partner engagement unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3]},{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2,4]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4]}],"complexes":["MKS module"],"partners":["ERP44","PDI","ERP57","MARCHF6","NEK4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96J42","full_name":"Thioredoxin domain-containing protein 15","aliases":[],"length_aa":360,"mass_kda":39.9,"function":"Acts as a positive regulator of ciliary hedgehog signaling (By similarity). Involved in ciliogenesis (PubMed:27894351)","subcellular_location":"Cell projection, cilium membrane","url":"https://www.uniprot.org/uniprotkb/Q96J42/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TXNDC15","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CCDC47","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/TXNDC15","total_profiled":1310},"omim":[{"mim_id":"619879","title":"MECKEL SYNDROME 14; MKS14","url":"https://www.omim.org/entry/619879"},{"mim_id":"617778","title":"THIOREDOXIN DOMAIN-CONTAINING PROTEIN 15; TXNDC15","url":"https://www.omim.org/entry/617778"},{"mim_id":"249000","title":"MECKEL SYNDROME, TYPE 1; MKS1","url":"https://www.omim.org/entry/249000"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TXNDC15"},"hgnc":{"alias_symbol":["TMX5","FLJ22625","2310047H23Rik"],"prev_symbol":["C5orf14"]},"alphafold":{"accession":"Q96J42","domains":[{"cath_id":"3.40.30.10","chopping":"192-312","consensus_level":"high","plddt":92.0402,"start":192,"end":312}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96J42","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96J42-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96J42-F1-predicted_aligned_error_v6.png","plddt_mean":64.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TXNDC15","jax_strain_url":"https://www.jax.org/strain/search?query=TXNDC15"},"sequence":{"accession":"Q96J42","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96J42.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96J42/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96J42"}},"corpus_meta":[{"pmid":"32878123","id":"PMC_32878123","title":"Thioredoxin-Related Transmembrane Proteins: TMX1 and Little Brothers TMX2, TMX3, TMX4 and TMX5.","date":"2020","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/32878123","citation_count":39,"is_preprint":false},{"pmid":"30851085","id":"PMC_30851085","title":"A prenatally diagnosed case of Meckel-Gruber syndrome with novel compound heterozygous pathogenic variants in the TXNDC15 gene.","date":"2019","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30851085","citation_count":9,"is_preprint":false},{"pmid":"38073519","id":"PMC_38073519","title":"First preimplantation genetic testing case of Meckel syndrome with a novel homozygous TXNDC15 variant in a non-consanguineous Chinese family.","date":"2023","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38073519","citation_count":7,"is_preprint":false},{"pmid":"38156946","id":"PMC_38156946","title":"Novel homozygous mutations in TXNDC15 causing Meckel syndrome.","date":"2023","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38156946","citation_count":4,"is_preprint":false},{"pmid":"39348940","id":"PMC_39348940","title":"TMX5/TXNDC15, a natural trapping mutant of the PDI family is a client of the proteostatic factor ERp44.","date":"2024","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/39348940","citation_count":3,"is_preprint":false},{"pmid":"39304719","id":"PMC_39304719","title":"Biallelic TXNDC15 variants associated with Joubert syndrome-related molar tooth sign and forebrain malformation.","date":"2024","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39304719","citation_count":2,"is_preprint":false},{"pmid":"41518077","id":"PMC_41518077","title":"CRISPR-Cas9-Generated TXNDC15 c.560delA Homozygous Mouse Model Exhibits Meckel-Gruber Syndrome Phenotype.","date":"2026","source":"Genesis (New York, N.Y. : 2000)","url":"https://pubmed.ncbi.nlm.nih.gov/41518077","citation_count":1,"is_preprint":false},{"pmid":"39679447","id":"PMC_39679447","title":"TXNDC15, an ER-localized thioredoxin-like transmembrane protein, contributes to ciliary transition zone integrity.","date":"2024","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/39679447","citation_count":1,"is_preprint":false},{"pmid":"42214920","id":"PMC_42214920","title":"TXNDC15 suppresses lung adenocarcinoma progression by inducing NEK4-dependent G2/M entry blockade.","date":"2026","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/42214920","citation_count":0,"is_preprint":false},{"pmid":"41959069","id":"PMC_41959069","title":"Genetic dissection of rapid proteolysis identifies TXNDC15 as a key factor of ERAD and lipid homeostasis.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41959069","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.04.25329006","title":"Proteomic and genetic insights into ancestry-specific associations in Parkinson’s disease","date":"2025-06-06","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.04.25329006","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6566,"output_tokens":1927,"usd":0.024302,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8796,"output_tokens":2480,"usd":0.05299,"stage2_stop_reason":"end_turn"},"total_usd":0.077292,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2024,\n      \"finding\": \"TMX5/TXNDC15 covalently engages, via its active-site cysteine residue at position 220, a subset of secretory proteins—mainly single- and multipass Golgi-resident polypeptides—indicating it acts as a natural trapping mutant within the PDI family.\",\n      \"method\": \"Biochemical trapping/co-immunoprecipitation with active-site cysteine mutants; identification of covalently associated substrate proteins\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal covalent trapping with active-site mutagenesis, single lab, multiple substrate classes identified\",\n      \"pmids\": [\"39348940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TMX5/TXNDC15 interacts non-covalently and covalently (via non-catalytic cysteine residues) with PDI family members PDI, ERp57, and ERp44. The association with ERp44 requires a mixed disulfide between the catalytic cysteine 29 of ERp44 and the non-catalytic cysteines 114 and/or 124 of TMX5, and this interaction controls the ER/pre-Golgi localization of TMX5.\",\n      \"method\": \"Co-immunoprecipitation, cysteine mutagenesis (active-site and non-catalytic residues), subcellular localization assays\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-specific mutagenesis identifying precise cysteines, co-IP validation, single lab\",\n      \"pmids\": [\"39348940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TMX5/TXNDC15 lacks its own ER localization/retention sequence and relies on ERp44 engagement for proper intercompartmental (pre-Golgi) distribution, placing it in the same class as Ero1α, Ero1β, Prx4, ERAP1, and SUMF1.\",\n      \"method\": \"Subcellular localization experiments combined with cysteine mutagenesis abolishing ERp44 interaction; fractionation/immunofluorescence\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — localization tied functionally to specific interaction, single lab, orthogonal methods\",\n      \"pmids\": [\"39348940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TXNDC15-knockout cells exhibit defects in MKS (transition zone) module assembly and in ciliary membrane protein localization. Rescue experiments showed that exogenous expression of TXNDC15 constructs harboring MKS-associated variants in the thioredoxin domain failed to rescue these defects, and mutation of two cysteine residues within the thioredoxin domain also failed to rescue, indicating TXNDC15 controls transition zone integrity from outside the TZ via its thioredoxin domain.\",\n      \"method\": \"TXNDC15 knockout cell lines, rescue with wild-type and mutant constructs (disease-variant and cysteine mutants), immunofluorescence of TZ components and ciliary membrane proteins\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined cellular phenotype, multiple rescue constructs, cysteine mutagenesis, single lab\",\n      \"pmids\": [\"39679447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TXNDC15 is an essential factor in MARCHF6-mediated ER-associated protein degradation (ERAD). Loss of TXNDC15 impairs substrate (ABHD2) exit and degradation from the ER; this function is catalysis-independent. Loss of TXNDC15 also remodels the ER proteome and lipid homeostasis.\",\n      \"method\": \"Genome-wide CRISPR-based functional screen for ERAD substrates, TXNDC15 KO validation, proteomic analysis of ER proteome and lipidomics, catalytic mutant rescue experiments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen plus KO validation with proteomic and lipidomic readouts, catalysis-independent mechanism established by mutant rescue, preprint single lab\",\n      \"pmids\": [\"41959069\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"A CRISPR-Cas9 mouse model homozygous for the frameshift variant Txndc15 c.512delA (equivalent to human c.560delA) exhibits the complete Meckel-Gruber syndrome phenotype at embryonic day 15.5, including fetal lethality, exencephaly, omphalocele, postaxial polydactyly, and polycystic kidneys, with markedly reduced TXNDC15 protein in brain, liver, and kidney, confirming TXNDC15 as a bona fide MKS disease gene.\",\n      \"method\": \"CRISPR-Cas9 knock-in mouse model; embryo phenotyping at E15.5; Western blot for TXNDC15 protein levels in tissues\",\n      \"journal\": \"Genesis (New York, N.Y. : 2000)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vivo genetic model with complete phenotype recapitulation and protein-level validation, confirms causality of specific variant\",\n      \"pmids\": [\"41518077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TXNDC15 interacts with the mitotic kinase NEK4 and suppresses lung adenocarcinoma cell proliferation by inducing G2/M phase arrest, placing TXNDC15 as an upstream regulator of NEK4-dependent G2/M checkpoint control.\",\n      \"method\": \"Co-immunoprecipitation (TXNDC15–NEK4 interaction), loss-of-function assays, cell cycle analysis (G2/M arrest readout)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP and functional assay, single lab, no structural or mutagenesis confirmation of interaction interface\",\n      \"pmids\": [\"42214920\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TXNDC15/TMX5 is an ER-resident thioredoxin-related transmembrane PDI family member that lacks autonomous ER retention signals and relies on ERp44 engagement (via non-catalytic cysteines 114/124) for pre-Golgi localization; it covalently traps Golgi-resident substrates via its active-site cysteine C220 and supports MARCHF6-mediated ERAD through a catalysis-independent mechanism; in cilia biology, its thioredoxin domain is required—from outside the transition zone—for MKS module assembly and ciliary membrane protein gating, and loss of the gene in mice fully recapitulates Meckel-Gruber syndrome.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TXNDC15 (TMX5) is an ER-resident thioredoxin-related transmembrane member of the protein disulfide isomerase (PDI) family that links redox-dependent disulfide chemistry to protein quality control, secretory trafficking, and ciliary signaling [#0, #2]. It functions as a natural \\\"trapping mutant\\\" within the PDI family, using its active-site cysteine C220 to covalently engage a subset of single- and multipass Golgi-resident secretory proteins [#0]. TXNDC15 lacks its own ER retention signal and instead achieves its ER/pre-Golgi localization through engagement of ERp44, a mixed disulfide forming between the catalytic cysteine of ERp44 and the non-catalytic cysteines C114/C124 of TXNDC15; it also associates with PDI and ERp57 [#1, #2]. Beyond substrate trapping, TXNDC15 is an essential, catalysis-independent factor in MARCHF6-mediated ER-associated degradation, where its loss impairs substrate (ABHD2) exit and degradation and remodels the ER proteome and lipid homeostasis [#4]. In cilia biology, its thioredoxin domain is required\\u2014acting from outside the transition zone\\u2014for assembly of the MKS module and proper gating of ciliary membrane proteins, with both disease-associated thioredoxin-domain variants and cysteine mutations failing to rescue knockout defects [#3]. A frameshift knock-in mouse fully recapitulates Meckel-Gruber syndrome, establishing TXNDC15 as a bona fide MKS disease gene [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2024,\n      \"claim\": \"Defining how an active-site PDI-family cysteine engages secretory cargo answered whether TXNDC15 acts catalytically or as a trap, establishing it as a covalent substrate-capturing oxidoreductase.\",\n      \"evidence\": \"Biochemical covalent trapping and co-IP with active-site cysteine mutants identifying Golgi-resident substrates\",\n      \"pmids\": [\"39348940\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate release/turnover mechanism not resolved\", \"Physiological consequence of trapping individual substrates not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Mapping the precise cysteines mediating ERp44 binding answered how a retention-signal-less protein is localized, showing TXNDC15 distribution is enforced by a mixed-disulfide handoff rather than an intrinsic motif.\",\n      \"evidence\": \"Co-IP plus active-site and non-catalytic cysteine mutagenesis and subcellular localization assays\",\n      \"pmids\": [\"39348940\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Dynamics of ERp44 cycling not characterized\", \"Whether PDI/ERp57 associations are functional or incidental unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking TXNDC15 thioredoxin-domain integrity to transition-zone assembly answered how a disease gene contributes to ciliogenesis, showing it controls MKS module assembly and ciliary membrane gating remotely via redox-relevant cysteines.\",\n      \"evidence\": \"Knockout cells with wild-type, disease-variant, and cysteine-mutant rescue and immunofluorescence of TZ and ciliary membrane components\",\n      \"pmids\": [\"39679447\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ciliary substrate(s) of TXNDC15 not identified\", \"Mechanism connecting ER-located activity to transition-zone integrity unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identifying TXNDC15 as essential for MARCHF6-dependent ERAD answered whether its quality-control role requires catalysis, showing a catalysis-independent function in substrate exit and degradation that also shapes ER lipid homeostasis.\",\n      \"evidence\": \"Genome-wide CRISPR screen, KO validation, catalytic mutant rescue, ER proteomics and lipidomics (preprint)\",\n      \"pmids\": [\"41959069\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of catalysis-independent ERAD support unknown\", \"Whether TXNDC15 directly contacts MARCHF6 not shown\", \"Preprint, single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"An in vivo frameshift model answered whether loss of TXNDC15 is causal for Meckel-Gruber syndrome, confirming complete phenotype recapitulation and disease-gene status.\",\n      \"evidence\": \"CRISPR-Cas9 knock-in mouse, E15.5 embryo phenotyping, tissue Western blot for TXNDC15\",\n      \"pmids\": [\"41518077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific contribution to each malformation not dissected\", \"Link between molecular redox/ERAD function and organ phenotypes not mechanistically traced\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"A reported TXNDC15-NEK4 interaction raised a potential cell-cycle/tumor-suppressive role, implicating TXNDC15 in G2/M checkpoint control in lung adenocarcinoma.\",\n      \"evidence\": \"Co-IP and loss-of-function cell cycle analysis\",\n      \"pmids\": [\"42214920\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation or interaction-interface mapping\", \"No structural or mutagenesis confirmation\", \"Mechanism linking an ER oxidoreductase to mitotic NEK4 unexplained\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How TXNDC15's ER redox/ERAD activities mechanistically produce its ciliary transition-zone and developmental functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying mechanism connecting ER-localized disulfide chemistry to transition-zone assembly\", \"Direct ciliary and ERAD substrates incompletely defined\", \"Structural basis of substrate/partner engagement unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"MKS module\"],\n    \"partners\": [\"ERp44\", \"PDI\", \"ERp57\", \"MARCHF6\", \"NEK4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}