{"gene":"SLC35A1","run_date":"2026-06-10T07:46:33","timeline":{"discoveries":[{"year":2014,"finding":"SLC35A1 deficiency impairs α-dystroglycan O-mannosylation independently of sialic acid; lentiviral complementation with disease mutation p.Q101H failed to restore O-mannosylation in SLC35A1 knockout cells but partly restored sialylation, demonstrating a role for SLC35A1 in α-DG O-mannosylation distinct from its CMP-sialic acid transport function.","method":"SLC35A1-knockout cell model (HAP1), lentiviral complementation with wild-type and p.Q101H mutant, α-DG ligand-binding assay, sialic acid incorporation assay","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays (KO complementation, ligand binding, sialylation rescue) in a single study with mechanistically distinct findings","pmids":["25552652"],"is_preprint":false},{"year":2020,"finding":"CDG-causing mutations Q101H, T156R, and E196K differentially impair SLC35A1 transporter function and dimer formation; all mutants retain correct Golgi localization. Single T156R and E196K mutants partially restore sialylation in CST-deficient HEK293T cells, whereas the compound T156R/E196K combination strongly reduces functionality, and differences in dimer formation capacity were observed among variants.","method":"Expression of mutant SLC35A1 variants in CST-deficient HEK293T cells, lectin staining, N- and O-glycan MS analysis, glycolipid analysis, microscopy for Golgi localization, dimer formation assay","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (glycan MS, lectins, localization, dimer assay) in a single lab study","pmids":["33396746"],"is_preprint":false},{"year":2021,"finding":"SLC35A1 transports CDP-ribitol into the Golgi in addition to CMP-sialic acid; the large binding pocket of SLC35A1 accommodates both substrates. Introducing bulky residues from SLC35A4 into the SLC35A1 binding pocket abolished sialylation but retained CDP-ribitol transport and ribitol phosphorylation of α-dystroglycan, demonstrating that binding-pocket size determines substrate specificity and that SLC35A1 and SLC35A4 redundantly transport CDP-ribitol.","method":"Site-directed mutagenesis of SLC35A1 binding pocket, expression in SLC35A1 KO cell lines, sialylation assay, ribitol phosphorylation assay of α-dystroglycan","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of active-site binding pocket with dual functional readouts (sialylation and ribitol phosphorylation) in KO complementation, single lab but multiple orthogonal methods","pmids":["34015330"],"is_preprint":false},{"year":2021,"finding":"Megakaryocyte/platelet-specific deletion of Slc35a1 in mice causes thrombocytopenia through two mechanisms: impaired megakaryocyte maturation in bone marrow and accelerated clearance of desialylated platelets by Kupffer cells in the liver.","method":"Conditional Slc35a1 knockout mice (Plt Slc35a1−/−), bone marrow megakaryocyte analysis, platelet count, liver histology, lectin staining for desialylation","journal":"Haematologica","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO mouse with multiple defined cellular phenotypes (megakaryocytopoiesis impairment and platelet clearance) replicated across multiple assays in vivo","pmids":["32303557"],"is_preprint":false},{"year":2022,"finding":"SLC35A1 physically associates with the α2,3-sialyltransferase ST3Gal4 in the Golgi; this interaction is disrupted by the CDG-causing E196K mutation (but not T156R), and the E196K mutant is less efficient at restoring N-glycan sialylation in SLC35A1-KO cells, suggesting the transporter–sialyltransferase complex is functionally important for N-glycan sialylation.","method":"Co-immunoprecipitation of SLC35A1 with ST3Gal4, expression of CDG mutants (E196K, T156R) in SLC35A1-KO cells, lectin/glycan analysis of N-glycan sialylation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus functional KO complementation assay, single lab, two orthogonal methods","pmids":["36257191"],"is_preprint":false},{"year":2024,"finding":"Endothelial-specific Slc35a1 deletion in mice causes desialylation of VEGFR2 in liver sinusoidal endothelial cells (LSECs), leading to enhanced VEGFR2 signaling, sinusoidal capillarization, disrupted hepatic zonation, and excessive neonatal lipid deposition; pharmacological inhibition of VEGFR2 with SU5416 rescued lipid deposition and hepatic vasculature, placing SLC35A1-mediated sialylation upstream of VEGFR2 signaling in LSEC identity.","method":"Endothelial-specific Slc35a1 knockout mice, immunofluorescence, immunoblot, RNA sequencing, lipidomic profiling, VEGFR2 signaling analysis, SU5416 pharmacological rescue","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO mouse with pharmacological epistasis rescue, multiple orthogonal readouts (lipidomics, transcriptomics, signaling assays, histology), single lab","pmids":["38467191"],"is_preprint":false},{"year":2021,"finding":"Knockout of SLC35A1 in HEK293T and HeLa cells eliminates cell-surface sialic acid, thereby unmasking terminal galactose residues and rendering cells permissive to AAV9 transduction, demonstrating that SLC35A1-dependent sialylation masks the galactose-based AAV9 receptor on these cells.","method":"CRISPR/Cas9 KO of SLC35A1 in HEK293T and HeLa cells, AAV9 transduction assay, lectin staining for cell-surface sialic acid and galactose","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined molecular mechanism (sialic acid masking of galactose) validated by lectin staining and functional transduction assay, single lab","pmids":["34069698"],"is_preprint":false},{"year":2024,"finding":"SLC35A1 KO reduces α2,6-linked sialic acid expression and impairs nuclear import of multiple rAAV serotypes post-internalization; deletion of the C-terminal cytoplasmic tail of SLC35A1 significantly decreases rAAV transduction and vector nuclear import without drastically reducing sialic acid expression, while the T128A mutant reduces sialic acid but still supports rAAV transduction, indicating the C-tail has a sialylation-independent role in rAAV intracellular trafficking.","method":"Genome-wide CRISPR/Cas9 KO screen, SLC35A1 KO and domain-deletion/point-mutant (ΔC-tail, T128A) cell lines, rAAV transduction assays across multiple serotypes, flow cytometry for surface sialic acid, nuclear import assay","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mutagenesis with functional separation of sialylation vs. nuclear import phenotypes, multiple AAV serotypes tested, single lab","pmids":["39601564"],"is_preprint":false},{"year":2022,"finding":"SLC35A1 KO in LLC-PK1 cells reduces cell-surface sialic acid and decreases porcine deltacoronavirus (PDCoV) adsorption; trypsin treatment promotes SA-dependent PDCoV entry. The T182 residue in the PDCoV S1 N-terminal domain was identified as a putative SA-binding site, placing SLC35A1-mediated sialylation at the viral attachment step.","method":"Genome-wide CRISPR/Cas9 KO screen in LLC-PK1 cells, SLC35A1 KO validation, viral adsorption assay, recombinant PDCoV with S1 domain mutations, trypsin treatment, lectin staining","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with viral adsorption functional assay and site-directed mutagenesis of viral binding domain, single lab","pmids":["36453883"],"is_preprint":false},{"year":2019,"finding":"Loss of SLC35A1 (the sialic acid transporter) affects cell survival upon VSV infection and modulates the apoptotic response induced by VSV, implicating SLC35A1 in the host apoptotic response to oncolytic virus infection.","method":"Focused CRISPR/Cas9 KO library genetic screen for cell survival upon VSV infection, follow-up characterization of SLC35A1 KO cells","journal":"Scientific reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — genetic screen with limited mechanistic follow-up, single lab, no direct molecular mechanism established beyond the apoptotic response association","pmids":["31320712"],"is_preprint":false},{"year":2025,"finding":"The SLC35A1 p.Thr45Ala disease variant does not directly impair CMP-Neu5Ac transport (as restoration of CMP-Neu5Ac levels was achieved in KO cells transfected with the variant), but causes reduced protein stability (~65% residual activity), leading to impaired sialylation of ICAM1, GP130, and TGN46, altered N-glycans, and secondary effects on O-GlcNAcylation, energy, and lipid metabolism.","method":"CRISPR/Cas9 SLC35A1 KO HEK293 cells complemented with WT or p.Thr45Ala variant, CMP-Neu5Ac measurement, lectin staining, LC-MS N-glycan analysis, immunoblot, patient fibroblast analysis, GlcNAc supplementation rescue","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO complementation with metabolite measurement and multiple glycan readouts, single lab, distinguishes stability from transport function via direct assay","pmids":["40613041"],"is_preprint":false}],"current_model":"SLC35A1 is a Golgi-localized CMP-sialic acid transporter that imports CMP-sialic acid from the cytoplasm into the Golgi for sialylation of glycoproteins and glycolipids; its large binding pocket also redundantly transports CDP-ribitol (with SLC35A4) for α-dystroglycan ribitol phosphorylation; it physically associates with the sialyltransferase ST3Gal4 to facilitate N-glycan sialylation; SLC35A1-mediated sialylation is required for normal megakaryocyte maturation and platelet homeostasis, for LSEC identity via regulation of VEGFR2 sialylation and signaling, and for viral attachment of sialic-acid-dependent viruses; additionally, the C-terminal cytoplasmic tail of SLC35A1 has a sialylation-independent role in intracellular trafficking of AAV vectors."},"narrative":{"mechanistic_narrative":"SLC35A1 is a Golgi nucleotide-sugar transporter that imports CMP-sialic acid from the cytoplasm to supply the Golgi sialylation machinery for glycoprotein and glycolipid sialylation [PMID:34015330, PMID:40613041]. Its substrate range is set by the size of its binding pocket, which is large enough to also accommodate CDP-ribitol; engineering bulky SLC35A4-derived residues into the pocket abolishes sialylation while preserving CDP-ribitol transport and α-dystroglycan ribitol phosphorylation, establishing that SLC35A1 and SLC35A4 redundantly transport CDP-ribitol [PMID:34015330]. SLC35A1 physically associates with the α2,3-sialyltransferase ST3Gal4 in the Golgi, and disruption of this transporter–sialyltransferase complex impairs N-glycan sialylation [PMID:36257191]. Through its control of sialylation, SLC35A1 governs megakaryocyte maturation and platelet homeostasis—its loss causing thrombocytopenia via defective megakaryocytopoiesis and accelerated clearance of desialylated platelets [PMID:32303557]—and maintains liver sinusoidal endothelial cell identity by restraining VEGFR2 signaling through VEGFR2 sialylation [PMID:38467191]. Because SLC35A1-dependent sialylation builds the terminal sialic acid coat of cell-surface glycans, it determines susceptibility to sialic-acid-dependent viruses and masks underlying galactose receptors [PMID:34069698, PMID:36453883]. Distinct from its transport activity, the C-terminal cytoplasmic tail of SLC35A1 has a sialylation-independent role in intracellular trafficking and nuclear import of recombinant AAV vectors [PMID:39601564]. Disease-causing variants act through several mechanisms: differential impairment of transport and dimer formation [PMID:33396746], reduced protein stability [PMID:40613041], and a sialylation-independent defect in α-dystroglycan O-mannosylation [PMID:25552652].","teleology":[{"year":2014,"claim":"Asked whether SLC35A1 contributes to glycosylation beyond CMP-sialic acid transport, revealing a sialylation-independent role in α-dystroglycan O-mannosylation.","evidence":"SLC35A1-knockout HAP1 cells with lentiviral WT and p.Q101H complementation, α-DG ligand-binding and sialic acid incorporation assays","pmids":["25552652"],"confidence":"High","gaps":["Molecular basis linking SLC35A1 to O-mannosylation not defined","Does not identify the relevant transported substrate for this function"]},{"year":2021,"claim":"Defined the structural determinant of substrate choice, showing the binding-pocket size lets SLC35A1 transport CDP-ribitol redundantly with SLC35A4 in addition to CMP-sialic acid.","evidence":"Site-directed mutagenesis of the SLC35A1 binding pocket expressed in KO cells, with sialylation and α-DG ribitol phosphorylation readouts","pmids":["34015330"],"confidence":"High","gaps":["No high-resolution structure of the transporter with either substrate","Stoichiometry/antiport coupling not established"]},{"year":2021,"claim":"Established the in vivo physiological consequence of SLC35A1-dependent sialylation in hematopoiesis, defining two mechanisms of thrombocytopenia.","evidence":"Megakaryocyte/platelet-specific conditional Slc35a1 knockout mice with bone marrow, platelet count, and liver clearance analysis","pmids":["32303557"],"confidence":"High","gaps":["Specific desialylated platelet glycoproteins driving clearance not enumerated","Megakaryocyte maturation block mechanism not resolved at molecular level"]},{"year":2021,"claim":"Connected SLC35A1 surface-sialylation to viral tropism, showing its loss unmasks the galactose AAV9 receptor.","evidence":"CRISPR/Cas9 KO of SLC35A1 in HEK293T/HeLa with AAV9 transduction and lectin staining","pmids":["34069698"],"confidence":"Medium","gaps":["Did not separate surface-receptor masking from intracellular trafficking roles","Single cell-line context"]},{"year":2021,"claim":"Characterized how CDG-causing mutations differentially perturb transport and oligomerization while preserving Golgi targeting.","evidence":"Expression of Q101H, T156R, E196K variants in CST-deficient HEK293T cells with glycan MS, lectins, localization and dimer assays","pmids":["33396746"],"confidence":"Medium","gaps":["Functional significance of dimerization for transport not directly tested","Genotype-phenotype correlation in patients not established"]},{"year":2022,"claim":"Identified a physical transporter–sialyltransferase complex, showing SLC35A1 associates with ST3Gal4 to promote N-glycan sialylation.","evidence":"Co-immunoprecipitation of SLC35A1 with ST3Gal4 and CDG-mutant complementation in SLC35A1-KO cells","pmids":["36257191"],"confidence":"Medium","gaps":["Single Co-IP without reciprocal or structural validation","Whether the interaction is direct or bridged is unknown"]},{"year":2022,"claim":"Extended the viral-attachment role to coronaviruses, placing SLC35A1-mediated sialylation at the PDCoV adsorption step.","evidence":"Genome-wide CRISPR KO screen in LLC-PK1 cells, viral adsorption assays, and recombinant PDCoV S1 mutagenesis","pmids":["36453883"],"confidence":"Medium","gaps":["Specific sialylated receptor used by PDCoV not defined","Single cell-line system"]},{"year":2024,"claim":"Demonstrated an organ-level requirement for SLC35A1 sialylation in maintaining endothelial identity by restraining VEGFR2 signaling.","evidence":"Endothelial-specific Slc35a1 knockout mice with transcriptomics, lipidomics, signaling analysis, and SU5416 pharmacological epistasis rescue","pmids":["38467191"],"confidence":"High","gaps":["Direct demonstration of VEGFR2 sialylation site not provided","Whether other endothelial receptors contribute is unresolved"]},{"year":2024,"claim":"Separated the transport function from a sialylation-independent role of the C-terminal tail in rAAV nuclear import.","evidence":"Genome-wide CRISPR screen with ΔC-tail and T128A mutant cell lines, multi-serotype rAAV transduction and nuclear import assays","pmids":["39601564"],"confidence":"Medium","gaps":["Mechanism by which the cytoplasmic tail directs vector trafficking unknown","Cellular trafficking partners of the C-tail not identified"]},{"year":2025,"claim":"Showed a disease variant can act through protein destabilization rather than direct transport loss, broadening the mutational mechanisms underlying SLC35A1-related disease.","evidence":"CRISPR KO HEK293 complemented with WT or p.Thr45Ala, CMP-Neu5Ac measurement, N-glycan LC-MS, immunoblot, and patient fibroblast analysis","pmids":["40613041"],"confidence":"Medium","gaps":["Structural basis of destabilization not defined","Downstream metabolic effects only correlative"]},{"year":null,"claim":"How the C-terminal tail mediates intracellular trafficking and what molecular partners distinguish SLC35A1's transport-independent roles from its CMP-sialic acid/CDP-ribitol transport function remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the transporter or its tail","Trafficking partners of the cytoplasmic tail unidentified","Mechanism of the O-mannosylation contribution undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[2,10]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[1,4]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,4,10]}],"complexes":[],"partners":["ST3GAL4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P78382","full_name":"CMP-sialic acid transporter","aliases":["Solute carrier family 35 member A1"],"length_aa":337,"mass_kda":36.8,"function":"Transports CMP-sialic acid from the cytosol into the Golgi apparatus, functioning as an antiporter that exchanges CMP-sialic acid for CMP (PubMed:12682060, PubMed:15576474, PubMed:23873973). Binds both CMP-sialic acid and free CMP, but has higher affinity for free CMP (By similarity). Also able to exchange CMP-sialic acid for AMP and UMP (PubMed:12682060). Also mediates the transport of CDP-ribitol (By similarity)","subcellular_location":"Golgi apparatus membrane; Golgi apparatus","url":"https://www.uniprot.org/uniprotkb/P78382/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC35A1","classification":"Not Classified","n_dependent_lines":80,"n_total_lines":1208,"dependency_fraction":0.06622516556291391},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SLC35A1","total_profiled":1310},"omim":[{"mim_id":"605634","title":"SOLUTE CARRIER FAMILY 35 (CMP-SIALIC ACID TRANSPORTER), MEMBER 1; SLC35A1","url":"https://www.omim.org/entry/605634"},{"mim_id":"603585","title":"CONGENITAL DISORDER OF GLYCOSYLATION, TYPE IIf; CDG2F","url":"https://www.omim.org/entry/603585"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SLC35A1"},"hgnc":{"alias_symbol":["CMPST","hCST","CMP-Sia-Tr"],"prev_symbol":[]},"alphafold":{"accession":"P78382","domains":[{"cath_id":"-","chopping":"9-161_171-316","consensus_level":"medium","plddt":92.5933,"start":9,"end":316}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P78382","model_url":"https://alphafold.ebi.ac.uk/files/AF-P78382-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P78382-F1-predicted_aligned_error_v6.png","plddt_mean":88.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC35A1","jax_strain_url":"https://www.jax.org/strain/search?query=SLC35A1"},"sequence":{"accession":"P78382","fasta_url":"https://rest.uniprot.org/uniprotkb/P78382.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P78382/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P78382"}},"corpus_meta":[{"pmid":"32303557","id":"PMC_32303557","title":"Slc35a1 deficiency causes thrombocytopenia due to impaired megakaryocytopoiesis and excessive platelet clearance in the liver.","date":"2021","source":"Haematologica","url":"https://pubmed.ncbi.nlm.nih.gov/32303557","citation_count":33,"is_preprint":false},{"pmid":"25552652","id":"PMC_25552652","title":"Disease mutations in CMP-sialic acid transporter SLC35A1 result in abnormal α-dystroglycan O-mannosylation, independent from sialic acid.","date":"2014","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25552652","citation_count":31,"is_preprint":false},{"pmid":"36453883","id":"PMC_36453883","title":"Genome-Wide CRISPR/Cas9 Screen Reveals a Role for SLC35A1 in the Adsorption of Porcine Deltacoronavirus.","date":"2022","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/36453883","citation_count":30,"is_preprint":false},{"pmid":"37499712","id":"PMC_37499712","title":"Genome-scale CRISPR screen identifies TRIM2 and SLC35A1 associated with porcine epidemic diarrhoea virus infection.","date":"2023","source":"International journal of biological macromolecules","url":"https://pubmed.ncbi.nlm.nih.gov/37499712","citation_count":22,"is_preprint":false},{"pmid":"31320712","id":"PMC_31320712","title":"The transporters SLC35A1 and SLC30A1 play opposite roles in cell survival upon VSV virus infection.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31320712","citation_count":20,"is_preprint":false},{"pmid":"33396746","id":"PMC_33396746","title":"Novel Insights into Selected Disease-Causing Mutations within the SLC35A1 Gene Encoding the CMP-Sialic Acid Transporter.","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33396746","citation_count":19,"is_preprint":false},{"pmid":"34015330","id":"PMC_34015330","title":"The promiscuous binding pocket of SLC35A1 ensures redundant transport of CDP-ribitol to the Golgi.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34015330","citation_count":19,"is_preprint":false},{"pmid":"34069698","id":"PMC_34069698","title":"Knockout of the CMP-Sialic Acid Transporter SLC35A1 in Human Cell Lines Increases Transduction Efficiency of Adeno-Associated Virus 9: Implications for Gene Therapy Potency Assays.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/34069698","citation_count":16,"is_preprint":false},{"pmid":"38467191","id":"PMC_38467191","title":"Endothelial Slc35a1 Deficiency Causes Loss of LSEC Identity and Exacerbates Neonatal Lipid Deposition in the Liver in Mice.","date":"2024","source":"Cellular and molecular gastroenterology and hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/38467191","citation_count":10,"is_preprint":false},{"pmid":"36257191","id":"PMC_36257191","title":"An interaction between SLC35A1 and ST3Gal4 is differentially affected by CDG-causing mutations in the SLC35A1 gene.","date":"2022","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/36257191","citation_count":8,"is_preprint":false},{"pmid":"39601564","id":"PMC_39601564","title":"Identification of SLC35A1 as an essential host factor for the transduction of multi-serotype recombinant adeno-associated virus (AAV) vectors.","date":"2024","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/39601564","citation_count":5,"is_preprint":false},{"pmid":"40613041","id":"PMC_40613041","title":"A Novel Missense Variant in Ultrarare SLC35A1-CDG Alters Cellular Glycosylation, Lipid, and Energy Metabolism Without Affecting CDG Serum Markers.","date":"2025","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/40613041","citation_count":1,"is_preprint":false},{"pmid":"39463973","id":"PMC_39463973","title":"Identification of SLC35A1 as an essential host factor for the transduction of multi-serotype recombinant adeno-associated virus (AAV) vectors.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/39463973","citation_count":0,"is_preprint":false},{"pmid":"42241751","id":"PMC_42241751","title":"Strain-specific responses of avian influenza virus to disruption of solute carrier family 35 member A1 (SLC35A1) in chicken cells.","date":"2026","source":"Poultry science","url":"https://pubmed.ncbi.nlm.nih.gov/42241751","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10139,"output_tokens":3358,"usd":0.040393,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10774,"output_tokens":3282,"usd":0.06796,"stage2_stop_reason":"end_turn"},"total_usd":0.108353,"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\": 2014,\n      \"finding\": \"SLC35A1 deficiency impairs α-dystroglycan O-mannosylation independently of sialic acid; lentiviral complementation with disease mutation p.Q101H failed to restore O-mannosylation in SLC35A1 knockout cells but partly restored sialylation, demonstrating a role for SLC35A1 in α-DG O-mannosylation distinct from its CMP-sialic acid transport function.\",\n      \"method\": \"SLC35A1-knockout cell model (HAP1), lentiviral complementation with wild-type and p.Q101H mutant, α-DG ligand-binding assay, sialic acid incorporation assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays (KO complementation, ligand binding, sialylation rescue) in a single study with mechanistically distinct findings\",\n      \"pmids\": [\"25552652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CDG-causing mutations Q101H, T156R, and E196K differentially impair SLC35A1 transporter function and dimer formation; all mutants retain correct Golgi localization. Single T156R and E196K mutants partially restore sialylation in CST-deficient HEK293T cells, whereas the compound T156R/E196K combination strongly reduces functionality, and differences in dimer formation capacity were observed among variants.\",\n      \"method\": \"Expression of mutant SLC35A1 variants in CST-deficient HEK293T cells, lectin staining, N- and O-glycan MS analysis, glycolipid analysis, microscopy for Golgi localization, dimer formation assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (glycan MS, lectins, localization, dimer assay) in a single lab study\",\n      \"pmids\": [\"33396746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SLC35A1 transports CDP-ribitol into the Golgi in addition to CMP-sialic acid; the large binding pocket of SLC35A1 accommodates both substrates. Introducing bulky residues from SLC35A4 into the SLC35A1 binding pocket abolished sialylation but retained CDP-ribitol transport and ribitol phosphorylation of α-dystroglycan, demonstrating that binding-pocket size determines substrate specificity and that SLC35A1 and SLC35A4 redundantly transport CDP-ribitol.\",\n      \"method\": \"Site-directed mutagenesis of SLC35A1 binding pocket, expression in SLC35A1 KO cell lines, sialylation assay, ribitol phosphorylation assay of α-dystroglycan\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of active-site binding pocket with dual functional readouts (sialylation and ribitol phosphorylation) in KO complementation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"34015330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Megakaryocyte/platelet-specific deletion of Slc35a1 in mice causes thrombocytopenia through two mechanisms: impaired megakaryocyte maturation in bone marrow and accelerated clearance of desialylated platelets by Kupffer cells in the liver.\",\n      \"method\": \"Conditional Slc35a1 knockout mice (Plt Slc35a1−/−), bone marrow megakaryocyte analysis, platelet count, liver histology, lectin staining for desialylation\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO mouse with multiple defined cellular phenotypes (megakaryocytopoiesis impairment and platelet clearance) replicated across multiple assays in vivo\",\n      \"pmids\": [\"32303557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLC35A1 physically associates with the α2,3-sialyltransferase ST3Gal4 in the Golgi; this interaction is disrupted by the CDG-causing E196K mutation (but not T156R), and the E196K mutant is less efficient at restoring N-glycan sialylation in SLC35A1-KO cells, suggesting the transporter–sialyltransferase complex is functionally important for N-glycan sialylation.\",\n      \"method\": \"Co-immunoprecipitation of SLC35A1 with ST3Gal4, expression of CDG mutants (E196K, T156R) in SLC35A1-KO cells, lectin/glycan analysis of N-glycan sialylation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus functional KO complementation assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"36257191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Endothelial-specific Slc35a1 deletion in mice causes desialylation of VEGFR2 in liver sinusoidal endothelial cells (LSECs), leading to enhanced VEGFR2 signaling, sinusoidal capillarization, disrupted hepatic zonation, and excessive neonatal lipid deposition; pharmacological inhibition of VEGFR2 with SU5416 rescued lipid deposition and hepatic vasculature, placing SLC35A1-mediated sialylation upstream of VEGFR2 signaling in LSEC identity.\",\n      \"method\": \"Endothelial-specific Slc35a1 knockout mice, immunofluorescence, immunoblot, RNA sequencing, lipidomic profiling, VEGFR2 signaling analysis, SU5416 pharmacological rescue\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO mouse with pharmacological epistasis rescue, multiple orthogonal readouts (lipidomics, transcriptomics, signaling assays, histology), single lab\",\n      \"pmids\": [\"38467191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Knockout of SLC35A1 in HEK293T and HeLa cells eliminates cell-surface sialic acid, thereby unmasking terminal galactose residues and rendering cells permissive to AAV9 transduction, demonstrating that SLC35A1-dependent sialylation masks the galactose-based AAV9 receptor on these cells.\",\n      \"method\": \"CRISPR/Cas9 KO of SLC35A1 in HEK293T and HeLa cells, AAV9 transduction assay, lectin staining for cell-surface sialic acid and galactose\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined molecular mechanism (sialic acid masking of galactose) validated by lectin staining and functional transduction assay, single lab\",\n      \"pmids\": [\"34069698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SLC35A1 KO reduces α2,6-linked sialic acid expression and impairs nuclear import of multiple rAAV serotypes post-internalization; deletion of the C-terminal cytoplasmic tail of SLC35A1 significantly decreases rAAV transduction and vector nuclear import without drastically reducing sialic acid expression, while the T128A mutant reduces sialic acid but still supports rAAV transduction, indicating the C-tail has a sialylation-independent role in rAAV intracellular trafficking.\",\n      \"method\": \"Genome-wide CRISPR/Cas9 KO screen, SLC35A1 KO and domain-deletion/point-mutant (ΔC-tail, T128A) cell lines, rAAV transduction assays across multiple serotypes, flow cytometry for surface sialic acid, nuclear import assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mutagenesis with functional separation of sialylation vs. nuclear import phenotypes, multiple AAV serotypes tested, single lab\",\n      \"pmids\": [\"39601564\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLC35A1 KO in LLC-PK1 cells reduces cell-surface sialic acid and decreases porcine deltacoronavirus (PDCoV) adsorption; trypsin treatment promotes SA-dependent PDCoV entry. The T182 residue in the PDCoV S1 N-terminal domain was identified as a putative SA-binding site, placing SLC35A1-mediated sialylation at the viral attachment step.\",\n      \"method\": \"Genome-wide CRISPR/Cas9 KO screen in LLC-PK1 cells, SLC35A1 KO validation, viral adsorption assay, recombinant PDCoV with S1 domain mutations, trypsin treatment, lectin staining\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with viral adsorption functional assay and site-directed mutagenesis of viral binding domain, single lab\",\n      \"pmids\": [\"36453883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of SLC35A1 (the sialic acid transporter) affects cell survival upon VSV infection and modulates the apoptotic response induced by VSV, implicating SLC35A1 in the host apoptotic response to oncolytic virus infection.\",\n      \"method\": \"Focused CRISPR/Cas9 KO library genetic screen for cell survival upon VSV infection, follow-up characterization of SLC35A1 KO cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — genetic screen with limited mechanistic follow-up, single lab, no direct molecular mechanism established beyond the apoptotic response association\",\n      \"pmids\": [\"31320712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The SLC35A1 p.Thr45Ala disease variant does not directly impair CMP-Neu5Ac transport (as restoration of CMP-Neu5Ac levels was achieved in KO cells transfected with the variant), but causes reduced protein stability (~65% residual activity), leading to impaired sialylation of ICAM1, GP130, and TGN46, altered N-glycans, and secondary effects on O-GlcNAcylation, energy, and lipid metabolism.\",\n      \"method\": \"CRISPR/Cas9 SLC35A1 KO HEK293 cells complemented with WT or p.Thr45Ala variant, CMP-Neu5Ac measurement, lectin staining, LC-MS N-glycan analysis, immunoblot, patient fibroblast analysis, GlcNAc supplementation rescue\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO complementation with metabolite measurement and multiple glycan readouts, single lab, distinguishes stability from transport function via direct assay\",\n      \"pmids\": [\"40613041\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC35A1 is a Golgi-localized CMP-sialic acid transporter that imports CMP-sialic acid from the cytoplasm into the Golgi for sialylation of glycoproteins and glycolipids; its large binding pocket also redundantly transports CDP-ribitol (with SLC35A4) for α-dystroglycan ribitol phosphorylation; it physically associates with the sialyltransferase ST3Gal4 to facilitate N-glycan sialylation; SLC35A1-mediated sialylation is required for normal megakaryocyte maturation and platelet homeostasis, for LSEC identity via regulation of VEGFR2 sialylation and signaling, and for viral attachment of sialic-acid-dependent viruses; additionally, the C-terminal cytoplasmic tail of SLC35A1 has a sialylation-independent role in intracellular trafficking of AAV vectors.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC35A1 is a Golgi nucleotide-sugar transporter that imports CMP-sialic acid from the cytoplasm to supply the Golgi sialylation machinery for glycoprotein and glycolipid sialylation [#2, #10]. Its substrate range is set by the size of its binding pocket, which is large enough to also accommodate CDP-ribitol; engineering bulky SLC35A4-derived residues into the pocket abolishes sialylation while preserving CDP-ribitol transport and α-dystroglycan ribitol phosphorylation, establishing that SLC35A1 and SLC35A4 redundantly transport CDP-ribitol [#2]. SLC35A1 physically associates with the α2,3-sialyltransferase ST3Gal4 in the Golgi, and disruption of this transporter–sialyltransferase complex impairs N-glycan sialylation [#4]. Through its control of sialylation, SLC35A1 governs megakaryocyte maturation and platelet homeostasis—its loss causing thrombocytopenia via defective megakaryocytopoiesis and accelerated clearance of desialylated platelets [#3]—and maintains liver sinusoidal endothelial cell identity by restraining VEGFR2 signaling through VEGFR2 sialylation [#5]. Because SLC35A1-dependent sialylation builds the terminal sialic acid coat of cell-surface glycans, it determines susceptibility to sialic-acid-dependent viruses and masks underlying galactose receptors [#6, #8]. Distinct from its transport activity, the C-terminal cytoplasmic tail of SLC35A1 has a sialylation-independent role in intracellular trafficking and nuclear import of recombinant AAV vectors [#7]. Disease-causing variants act through several mechanisms: differential impairment of transport and dimer formation [#1], reduced protein stability [#10], and a sialylation-independent defect in α-dystroglycan O-mannosylation [#0].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Asked whether SLC35A1 contributes to glycosylation beyond CMP-sialic acid transport, revealing a sialylation-independent role in α-dystroglycan O-mannosylation.\",\n      \"evidence\": \"SLC35A1-knockout HAP1 cells with lentiviral WT and p.Q101H complementation, α-DG ligand-binding and sialic acid incorporation assays\",\n      \"pmids\": [\"25552652\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis linking SLC35A1 to O-mannosylation not defined\", \"Does not identify the relevant transported substrate for this function\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the structural determinant of substrate choice, showing the binding-pocket size lets SLC35A1 transport CDP-ribitol redundantly with SLC35A4 in addition to CMP-sialic acid.\",\n      \"evidence\": \"Site-directed mutagenesis of the SLC35A1 binding pocket expressed in KO cells, with sialylation and α-DG ribitol phosphorylation readouts\",\n      \"pmids\": [\"34015330\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the transporter with either substrate\", \"Stoichiometry/antiport coupling not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established the in vivo physiological consequence of SLC35A1-dependent sialylation in hematopoiesis, defining two mechanisms of thrombocytopenia.\",\n      \"evidence\": \"Megakaryocyte/platelet-specific conditional Slc35a1 knockout mice with bone marrow, platelet count, and liver clearance analysis\",\n      \"pmids\": [\"32303557\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific desialylated platelet glycoproteins driving clearance not enumerated\", \"Megakaryocyte maturation block mechanism not resolved at molecular level\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected SLC35A1 surface-sialylation to viral tropism, showing its loss unmasks the galactose AAV9 receptor.\",\n      \"evidence\": \"CRISPR/Cas9 KO of SLC35A1 in HEK293T/HeLa with AAV9 transduction and lectin staining\",\n      \"pmids\": [\"34069698\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not separate surface-receptor masking from intracellular trafficking roles\", \"Single cell-line context\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Characterized how CDG-causing mutations differentially perturb transport and oligomerization while preserving Golgi targeting.\",\n      \"evidence\": \"Expression of Q101H, T156R, E196K variants in CST-deficient HEK293T cells with glycan MS, lectins, localization and dimer assays\",\n      \"pmids\": [\"33396746\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of dimerization for transport not directly tested\", \"Genotype-phenotype correlation in patients not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified a physical transporter–sialyltransferase complex, showing SLC35A1 associates with ST3Gal4 to promote N-glycan sialylation.\",\n      \"evidence\": \"Co-immunoprecipitation of SLC35A1 with ST3Gal4 and CDG-mutant complementation in SLC35A1-KO cells\",\n      \"pmids\": [\"36257191\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP without reciprocal or structural validation\", \"Whether the interaction is direct or bridged is unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended the viral-attachment role to coronaviruses, placing SLC35A1-mediated sialylation at the PDCoV adsorption step.\",\n      \"evidence\": \"Genome-wide CRISPR KO screen in LLC-PK1 cells, viral adsorption assays, and recombinant PDCoV S1 mutagenesis\",\n      \"pmids\": [\"36453883\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific sialylated receptor used by PDCoV not defined\", \"Single cell-line system\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated an organ-level requirement for SLC35A1 sialylation in maintaining endothelial identity by restraining VEGFR2 signaling.\",\n      \"evidence\": \"Endothelial-specific Slc35a1 knockout mice with transcriptomics, lipidomics, signaling analysis, and SU5416 pharmacological epistasis rescue\",\n      \"pmids\": [\"38467191\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct demonstration of VEGFR2 sialylation site not provided\", \"Whether other endothelial receptors contribute is unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Separated the transport function from a sialylation-independent role of the C-terminal tail in rAAV nuclear import.\",\n      \"evidence\": \"Genome-wide CRISPR screen with ΔC-tail and T128A mutant cell lines, multi-serotype rAAV transduction and nuclear import assays\",\n      \"pmids\": [\"39601564\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which the cytoplasmic tail directs vector trafficking unknown\", \"Cellular trafficking partners of the C-tail not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed a disease variant can act through protein destabilization rather than direct transport loss, broadening the mutational mechanisms underlying SLC35A1-related disease.\",\n      \"evidence\": \"CRISPR KO HEK293 complemented with WT or p.Thr45Ala, CMP-Neu5Ac measurement, N-glycan LC-MS, immunoblot, and patient fibroblast analysis\",\n      \"pmids\": [\"40613041\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of destabilization not defined\", \"Downstream metabolic effects only correlative\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the C-terminal tail mediates intracellular trafficking and what molecular partners distinguish SLC35A1's transport-independent roles from its CMP-sialic acid/CDP-ribitol transport function remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the transporter or its tail\", \"Trafficking partners of the cytoplasmic tail unidentified\", \"Mechanism of the O-mannosylation contribution undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [2, 10]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 4, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ST3Gal4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}