{"gene":"MFSD1","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2019,"finding":"MFSD1 is a lysosomal membrane protein that is not N-glycosylated and contains a dileucine-based sorting motif required for its transport to lysosomes. MFSD1 physically interacts with GLMP (glycosylated lysosomal membrane protein), and each protein is required for maintaining normal levels of the other in lysosomes. Mfsd1 knockout mice develop splenomegaly and severe liver disease.","method":"Knockout mouse model, proteomics of isolated lysosomes, co-immunoprecipitation, mutagenesis of sorting motif, immunofluorescence localization","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KO mice, proteomics, Co-IP, mutagenesis) in a single rigorous study","pmids":["31661432"],"is_preprint":false},{"year":2024,"finding":"MFSD1, in complex with its accessory subunit GLMP, functions as a general lysosomal dipeptide uniporter. Untargeted metabolomics of MFSD1-deficient lysosomes revealed accumulation of cationic dipeptides. Purified MFSD1 selectively bound diverse dipeptides. Electrophysiological, isotope tracer, and fluorescence-based studies in Xenopus oocytes and proteoliposomes demonstrated uniporter activity for cationic, neutral, and anionic dipeptides. Cryo-EM structure of the dipeptide-bound MFSD1-GLMP complex in outward-open conformation characterized the heterodimer interface and structural basis for dipeptide selectivity.","method":"Cryo-EM structure, metabolomics, electrophysiology (Xenopus oocytes), isotope tracer assay, fluorescence transport assay, proteoliposome reconstitution, molecular dynamics simulations","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in proteoliposomes, cryo-EM structure, electrophysiology, and metabolomics all converging on the same conclusion","pmids":["38839979"],"is_preprint":false},{"year":2024,"finding":"MFSD1 is a highly selective lysosomal dipeptide exporter functioning as a uniporter, preferentially transporting cationic dipeptides containing lysine, arginine, or histidine residues. Targeted metabolomics showed accumulation of lysine/arginine-containing dipeptides in MFSD1-deficient lysosomes. Whole-cell patch-clamp electrophysiology of HEK293 cells expressing MFSD1 at the cell surface revealed transport affinities in the lower mM range for positively charged dipeptides, while single amino acids, tripeptides, and negatively charged dipeptides were not transported.","method":"Targeted metabolomics, whole-cell patch-clamp electrophysiology in HEK293 cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — direct electrophysiological measurements combined with metabolomics, consistent with PMID 38839979","pmids":["38507452"],"is_preprint":false},{"year":2023,"finding":"MFSD1 forms a protein complex with both GLMP and GIMAP5 in lysosomes. The interactions of MFSD1 and GLMP with GIMAP5 are essential to maintain normal GIMAP5 expression, which in turn is critical for lymphocyte development and liver homeostasis. Germline knockout of Mfsd1, Glmp, or Gimap5 each caused lymphopenia, liver pathology, extramedullary hematopoiesis, and lipid deposition in bone marrow and liver.","method":"ENU mutagenesis screen, germline knockout mouse models, proteomic analysis (mass spectrometry) of protein associations","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple KO models with defined phenotypes, proteomic identification of complex members, genetic epistasis","pmids":["38055739"],"is_preprint":false},{"year":2022,"finding":"MFSD1 promotes recycling of endocytosed inactive β1 integrin back to the cell surface, protecting it from proteolytic degradation and thereby reducing the integrin activation index. Loss of MFSD1 leads to increased focal adhesion turnover, reduced stability of mature inactive β1 integrin, increased integrin activation, and enhanced tumor cell migration and metastasis in mouse models.","method":"MFSD1 knockout mouse metastasis models (experimental and spontaneous), cell migration assays, focal adhesion turnover assays, integrin activation index measurements, integrin recycling assays","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse models with defined cellular phenotype and mechanistic pathway placement, single lab","pmids":["35211397"],"is_preprint":false},{"year":2016,"finding":"MFSD1 is a putative solute carrier of the major facilitator superfamily, predicted to have 12 transmembrane regions based on homology modelling. It is expressed in neurons with protein staining along the plasma membrane in mice. Deprivation of amino acids in mouse embryonic primary cortex cells upregulates Mfsd1 expression.","method":"Phylogenetic analysis, homology modelling, immunofluorescence, amino acid deprivation experiment in primary cells","journal":"Journal of molecular neuroscience : MN","confidence":"Low","confidence_rationale":"Tier 3-4 — largely computational prediction of structure and SLC membership, with limited functional experiment","pmids":["27981419"],"is_preprint":false}],"current_model":"MFSD1 is a lysosomal membrane protein of the major facilitator superfamily that forms a tight complex with accessory subunit GLMP (and additionally associates with GIMAP5), requires a dileucine-based sorting motif for lysosomal targeting, and functions as a uniporter that exports diverse dipeptides—products of lysosomal proteolysis—from lysosomes back to the cytoplasm for biosynthetic reuse, with its cryo-EM structure revealing the heterodimer interface and structural basis for dipeptide selectivity; loss of MFSD1 causes lysosomal dipeptide accumulation, impaired β1 integrin recycling, lymphopenia, and severe liver disease in mice."},"narrative":{"teleology":[{"year":2016,"claim":"Before any functional data, computational analysis classified MFSD1 as a putative 12-transmembrane solute carrier of the major facilitator superfamily, with neuronal expression responsive to amino acid deprivation, establishing it as a candidate nutrient transporter.","evidence":"Phylogenetic analysis, homology modelling, immunofluorescence, and amino acid deprivation in mouse primary cortical cells","pmids":["27981419"],"confidence":"Low","gaps":["Predictions based on homology modelling without direct structural data","No transport substrate identified","Neuronal plasma membrane localization was later superseded by lysosomal localization findings"]},{"year":2019,"claim":"The first loss-of-function study established that MFSD1 is a lysosomal membrane protein requiring a dileucine sorting motif for targeting, that it forms a stabilizing complex with GLMP, and that its loss causes splenomegaly and severe liver disease in mice—demonstrating physiological importance but leaving the transport substrate unknown.","evidence":"Mfsd1 knockout mice, lysosomal proteomics, co-immunoprecipitation, mutagenesis of sorting motif, immunofluorescence","pmids":["31661432"],"confidence":"High","gaps":["No transport substrate identified","Mechanism linking MFSD1 loss to liver disease unresolved","Whether GLMP is a passive stabilizer or active functional partner not determined"]},{"year":2022,"claim":"A cell-biological study revealed that MFSD1 promotes recycling of inactive β1 integrin to the cell surface, connecting its loss to enhanced tumor cell migration and metastasis—an unexpected role beyond solute transport.","evidence":"MFSD1 knockout mouse metastasis models, integrin recycling assays, focal adhesion turnover measurements","pmids":["35211397"],"confidence":"Medium","gaps":["Whether the integrin recycling phenotype is a direct effect of MFSD1 or secondary to lysosomal dysfunction is unclear","Single-lab finding not yet independently replicated","Molecular mechanism by which a transporter regulates integrin trafficking not defined"]},{"year":2023,"claim":"Proteomic and genetic studies expanded the MFSD1–GLMP complex to include GIMAP5, showing that all three proteins are interdependent for expression and that loss of any one recapitulates lymphopenia, liver pathology, and lipid deposition—establishing a tripartite lysosomal complex essential for immune and metabolic homeostasis.","evidence":"ENU mutagenesis screen, germline knockout mouse models for Mfsd1/Glmp/Gimap5, mass spectrometry","pmids":["38055739"],"confidence":"High","gaps":["Whether GIMAP5 modulates MFSD1 transport activity or acts independently downstream is unknown","The mechanism linking lysosomal dipeptide export to lymphocyte development is not defined"]},{"year":2024,"claim":"Two independent studies converged to identify MFSD1 as a lysosomal dipeptide uniporter: untargeted and targeted metabolomics showed dipeptide accumulation in MFSD1-deficient lysosomes, electrophysiology and proteoliposome reconstitution demonstrated direct uniport of cationic, neutral, and anionic dipeptides, and cryo-EM of the MFSD1–GLMP heterodimer in the outward-open state revealed the structural basis for dipeptide binding and selectivity.","evidence":"Cryo-EM structure, proteoliposome reconstitution, Xenopus oocyte electrophysiology, whole-cell patch-clamp in HEK293 cells, untargeted and targeted metabolomics, molecular dynamics simulations","pmids":["38839979","38507452"],"confidence":"High","gaps":["Inward-open and occluded conformational states have not been resolved structurally","Physiological regulation of MFSD1 transport activity (e.g., by luminal pH, post-translational modifications) is undefined","Relative contributions of MFSD1 versus other peptide transporters (e.g., PQLC2, PHT1) to lysosomal peptide efflux are not quantified"]},{"year":null,"claim":"Key unresolved questions include the full conformational cycle of MFSD1 during transport, whether GIMAP5 directly modulates transport function, the molecular basis connecting dipeptide export to integrin recycling and immune phenotypes, and whether MFSD1 mutations cause human disease.","evidence":"","pmids":[],"confidence":"Low","gaps":["No human Mendelian disease linked to MFSD1 mutations","Structural basis for the complete transport cycle remains incomplete","Causal pathway from dipeptide accumulation to lymphopenia and liver disease not delineated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,2]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,1,2,3]}],"pathway":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,1,2,3]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,2]}],"complexes":["MFSD1–GLMP heterodimer","MFSD1–GLMP–GIMAP5 complex"],"partners":["GLMP","GIMAP5"],"other_free_text":[]},"mechanistic_narrative":"MFSD1 is a lysosomal major facilitator superfamily transporter that functions as a dipeptide uniporter, exporting cationic, neutral, and anionic dipeptides—products of lysosomal proteolysis—back to the cytoplasm for biosynthetic reuse [PMID:38839979, PMID:38507452]. MFSD1 forms an obligate heterodimeric complex with the accessory subunit GLMP, which stabilizes MFSD1 in lysosomes and is required for its normal expression; it additionally associates with GIMAP5, and loss of any member of this complex causes lymphopenia, liver disease, and extramedullary hematopoiesis in mice [PMID:31661432, PMID:38055739]. Lysosomal targeting of MFSD1 depends on a dileucine-based sorting motif, and its cryo-EM structure in the outward-open, dipeptide-bound state reveals the structural determinants of dipeptide selectivity and the GLMP interaction interface [PMID:31661432, PMID:38839979]. MFSD1 also promotes recycling of inactive β1 integrin to the cell surface, and its loss increases integrin activation, focal adhesion turnover, and metastatic potential in mouse tumor models [PMID:35211397]."},"prefetch_data":{"uniprot":{"accession":"Q9H3U5","full_name":"Lysosomal dipeptide transporter MFSD1","aliases":["Major facilitator superfamily domain-containing protein 1","Smooth muscle cell-associated protein 4","SMAP-4"],"length_aa":465,"mass_kda":51.2,"function":"Lysosomal dipeptide uniporter that selectively exports lysine, arginine or histidine-containing dipeptides with a net positive charge from the lysosome lumen into the cytosol (PubMed:38507452). Could play a role in a specific type of protein O-glycosylation indirectly regulating macrophages migration and tissue invasion (PubMed:30910009). Also essential for liver homeostasis (By similarity)","subcellular_location":"Lysosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9H3U5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MFSD1","classification":"Not Classified","n_dependent_lines":40,"n_total_lines":1208,"dependency_fraction":0.033112582781456956},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MFSD1","total_profiled":1310},"omim":[{"mim_id":"620308","title":"MAJOR FACILITATOR SUPERFAMILY DOMAIN-CONTAINING PROTEIN 3; MFSD3","url":"https://www.omim.org/entry/620308"},{"mim_id":"619976","title":"MAJOR FACILITATOR SUPERFAMILY DOMAIN-CONTAINING PROTEIN 1; MFSD1","url":"https://www.omim.org/entry/619976"},{"mim_id":"619958","title":"GLYCOSYLATED LYSOSOMAL MEMBRANE PROTEIN; GLMP","url":"https://www.omim.org/entry/619958"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MFSD1"},"hgnc":{"alias_symbol":["Minerva","SLC72A1","FLJ14153","UG0581B09"],"prev_symbol":[]},"alphafold":{"accession":"Q9H3U5","domains":[{"cath_id":"1.20.1250.20","chopping":"39-253","consensus_level":"medium","plddt":93.295,"start":39,"end":253},{"cath_id":"1.20.1250.20","chopping":"256-465","consensus_level":"medium","plddt":92.4234,"start":256,"end":465}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3U5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3U5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3U5-F1-predicted_aligned_error_v6.png","plddt_mean":88.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MFSD1","jax_strain_url":"https://www.jax.org/strain/search?query=MFSD1"},"sequence":{"accession":"Q9H3U5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H3U5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H3U5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3U5"}},"corpus_meta":[{"pmid":"23242262","id":"PMC_23242262","title":"Minerva and minepy: a C engine for the MINE suite and its R, Python and MATLAB wrappers.","date":"2012","source":"Bioinformatics (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/23242262","citation_count":81,"is_preprint":false},{"pmid":"2915248","id":"PMC_2915248","title":"A comparison of the Minerva and halo jackets for stabilization of the cervical spine.","date":"1989","source":"Journal of neurosurgery","url":"https://pubmed.ncbi.nlm.nih.gov/2915248","citation_count":35,"is_preprint":false},{"pmid":"27981419","id":"PMC_27981419","title":"The Novel Membrane-Bound Proteins MFSD1 and MFSD3 are Putative SLC Transporters Affected by Altered Nutrient Intake.","date":"2016","source":"Journal of molecular neuroscience : MN","url":"https://pubmed.ncbi.nlm.nih.gov/27981419","citation_count":32,"is_preprint":false},{"pmid":"21148485","id":"PMC_21148485","title":"FAM129B/MINERVA, a novel adherens junction-associated protein, suppresses apoptosis in HeLa cells.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21148485","citation_count":32,"is_preprint":false},{"pmid":"31661432","id":"PMC_31661432","title":"The lysosomal transporter MFSD1 is essential for liver homeostasis and critically depends on its accessory subunit GLMP.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/31661432","citation_count":26,"is_preprint":false},{"pmid":"33768192","id":"PMC_33768192","title":"Minerva: a light-weight, narrative image browser for multiplexed tissue images.","date":"2020","source":"Journal of open source software","url":"https://pubmed.ncbi.nlm.nih.gov/33768192","citation_count":21,"is_preprint":false},{"pmid":"33290743","id":"PMC_33290743","title":"MINERVA: A Facile Strategy for SARS-CoV-2 Whole-Genome Deep Sequencing of Clinical Samples.","date":"2020","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/33290743","citation_count":14,"is_preprint":false},{"pmid":"30523036","id":"PMC_30523036","title":"Minerva: an alignment- and reference-free approach to deconvolve Linked-Reads for metagenomics.","date":"2018","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/30523036","citation_count":12,"is_preprint":false},{"pmid":"22977259","id":"PMC_22977259","title":"Delayed cutaneous wound healing in Fam129b/Minerva-deficient mice.","date":"2012","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22977259","citation_count":11,"is_preprint":false},{"pmid":"37736017","id":"PMC_37736017","title":"Human gut epithelium features recapitulated in MINERVA 2.0 millifluidic organ-on-a-chip device.","date":"2023","source":"APL bioengineering","url":"https://pubmed.ncbi.nlm.nih.gov/37736017","citation_count":10,"is_preprint":false},{"pmid":"38055739","id":"PMC_38055739","title":"Essential role of MFSD1-GLMP-GIMAP5 in lymphocyte survival and liver homeostasis.","date":"2023","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/38055739","citation_count":8,"is_preprint":false},{"pmid":"38839979","id":"PMC_38839979","title":"MFSD1 with its accessory subunit GLMP functions as a general dipeptide uniporter in lysosomes.","date":"2024","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/38839979","citation_count":8,"is_preprint":false},{"pmid":"36648161","id":"PMC_36648161","title":"Exploration and comparison of molecular mechanisms across diseases using MINERVA Net.","date":"2023","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/36648161","citation_count":7,"is_preprint":false},{"pmid":"35211397","id":"PMC_35211397","title":"The Solute Carrier MFSD1 Decreases the Activation Status of β1 Integrin and Thus Tumor 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MFSD1 physically interacts with GLMP (glycosylated lysosomal membrane protein), and each protein is required for maintaining normal levels of the other in lysosomes. Mfsd1 knockout mice develop splenomegaly and severe liver disease.\",\n      \"method\": \"Knockout mouse model, proteomics of isolated lysosomes, co-immunoprecipitation, mutagenesis of sorting motif, immunofluorescence localization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KO mice, proteomics, Co-IP, mutagenesis) in a single rigorous study\",\n      \"pmids\": [\"31661432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MFSD1, in complex with its accessory subunit GLMP, functions as a general lysosomal dipeptide uniporter. Untargeted metabolomics of MFSD1-deficient lysosomes revealed accumulation of cationic dipeptides. Purified MFSD1 selectively bound diverse dipeptides. Electrophysiological, isotope tracer, and fluorescence-based studies in Xenopus oocytes and proteoliposomes demonstrated uniporter activity for cationic, neutral, and anionic dipeptides. Cryo-EM structure of the dipeptide-bound MFSD1-GLMP complex in outward-open conformation characterized the heterodimer interface and structural basis for dipeptide selectivity.\",\n      \"method\": \"Cryo-EM structure, metabolomics, electrophysiology (Xenopus oocytes), isotope tracer assay, fluorescence transport assay, proteoliposome reconstitution, molecular dynamics simulations\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in proteoliposomes, cryo-EM structure, electrophysiology, and metabolomics all converging on the same conclusion\",\n      \"pmids\": [\"38839979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MFSD1 is a highly selective lysosomal dipeptide exporter functioning as a uniporter, preferentially transporting cationic dipeptides containing lysine, arginine, or histidine residues. Targeted metabolomics showed accumulation of lysine/arginine-containing dipeptides in MFSD1-deficient lysosomes. Whole-cell patch-clamp electrophysiology of HEK293 cells expressing MFSD1 at the cell surface revealed transport affinities in the lower mM range for positively charged dipeptides, while single amino acids, tripeptides, and negatively charged dipeptides were not transported.\",\n      \"method\": \"Targeted metabolomics, whole-cell patch-clamp electrophysiology in HEK293 cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct electrophysiological measurements combined with metabolomics, consistent with PMID 38839979\",\n      \"pmids\": [\"38507452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MFSD1 forms a protein complex with both GLMP and GIMAP5 in lysosomes. The interactions of MFSD1 and GLMP with GIMAP5 are essential to maintain normal GIMAP5 expression, which in turn is critical for lymphocyte development and liver homeostasis. Germline knockout of Mfsd1, Glmp, or Gimap5 each caused lymphopenia, liver pathology, extramedullary hematopoiesis, and lipid deposition in bone marrow and liver.\",\n      \"method\": \"ENU mutagenesis screen, germline knockout mouse models, proteomic analysis (mass spectrometry) of protein associations\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple KO models with defined phenotypes, proteomic identification of complex members, genetic epistasis\",\n      \"pmids\": [\"38055739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MFSD1 promotes recycling of endocytosed inactive β1 integrin back to the cell surface, protecting it from proteolytic degradation and thereby reducing the integrin activation index. Loss of MFSD1 leads to increased focal adhesion turnover, reduced stability of mature inactive β1 integrin, increased integrin activation, and enhanced tumor cell migration and metastasis in mouse models.\",\n      \"method\": \"MFSD1 knockout mouse metastasis models (experimental and spontaneous), cell migration assays, focal adhesion turnover assays, integrin activation index measurements, integrin recycling assays\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse models with defined cellular phenotype and mechanistic pathway placement, single lab\",\n      \"pmids\": [\"35211397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"MFSD1 is a putative solute carrier of the major facilitator superfamily, predicted to have 12 transmembrane regions based on homology modelling. It is expressed in neurons with protein staining along the plasma membrane in mice. Deprivation of amino acids in mouse embryonic primary cortex cells upregulates Mfsd1 expression.\",\n      \"method\": \"Phylogenetic analysis, homology modelling, immunofluorescence, amino acid deprivation experiment in primary cells\",\n      \"journal\": \"Journal of molecular neuroscience : MN\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3-4 — largely computational prediction of structure and SLC membership, with limited functional experiment\",\n      \"pmids\": [\"27981419\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MFSD1 is a lysosomal membrane protein of the major facilitator superfamily that forms a tight complex with accessory subunit GLMP (and additionally associates with GIMAP5), requires a dileucine-based sorting motif for lysosomal targeting, and functions as a uniporter that exports diverse dipeptides—products of lysosomal proteolysis—from lysosomes back to the cytoplasm for biosynthetic reuse, with its cryo-EM structure revealing the heterodimer interface and structural basis for dipeptide selectivity; loss of MFSD1 causes lysosomal dipeptide accumulation, impaired β1 integrin recycling, lymphopenia, and severe liver disease in mice.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MFSD1 is a lysosomal major facilitator superfamily transporter that functions as a dipeptide uniporter, exporting cationic, neutral, and anionic dipeptides—products of lysosomal proteolysis—back to the cytoplasm for biosynthetic reuse [PMID:38839979, PMID:38507452]. MFSD1 forms an obligate heterodimeric complex with the accessory subunit GLMP, which stabilizes MFSD1 in lysosomes and is required for its normal expression; it additionally associates with GIMAP5, and loss of any member of this complex causes lymphopenia, liver disease, and extramedullary hematopoiesis in mice [PMID:31661432, PMID:38055739]. Lysosomal targeting of MFSD1 depends on a dileucine-based sorting motif, and its cryo-EM structure in the outward-open, dipeptide-bound state reveals the structural determinants of dipeptide selectivity and the GLMP interaction interface [PMID:31661432, PMID:38839979]. MFSD1 also promotes recycling of inactive β1 integrin to the cell surface, and its loss increases integrin activation, focal adhesion turnover, and metastatic potential in mouse tumor models [PMID:35211397].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Before any functional data, computational analysis classified MFSD1 as a putative 12-transmembrane solute carrier of the major facilitator superfamily, with neuronal expression responsive to amino acid deprivation, establishing it as a candidate nutrient transporter.\",\n      \"evidence\": \"Phylogenetic analysis, homology modelling, immunofluorescence, and amino acid deprivation in mouse primary cortical cells\",\n      \"pmids\": [\"27981419\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Predictions based on homology modelling without direct structural data\",\n        \"No transport substrate identified\",\n        \"Neuronal plasma membrane localization was later superseded by lysosomal localization findings\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The first loss-of-function study established that MFSD1 is a lysosomal membrane protein requiring a dileucine sorting motif for targeting, that it forms a stabilizing complex with GLMP, and that its loss causes splenomegaly and severe liver disease in mice—demonstrating physiological importance but leaving the transport substrate unknown.\",\n      \"evidence\": \"Mfsd1 knockout mice, lysosomal proteomics, co-immunoprecipitation, mutagenesis of sorting motif, immunofluorescence\",\n      \"pmids\": [\"31661432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No transport substrate identified\",\n        \"Mechanism linking MFSD1 loss to liver disease unresolved\",\n        \"Whether GLMP is a passive stabilizer or active functional partner not determined\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A cell-biological study revealed that MFSD1 promotes recycling of inactive β1 integrin to the cell surface, connecting its loss to enhanced tumor cell migration and metastasis—an unexpected role beyond solute transport.\",\n      \"evidence\": \"MFSD1 knockout mouse metastasis models, integrin recycling assays, focal adhesion turnover measurements\",\n      \"pmids\": [\"35211397\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the integrin recycling phenotype is a direct effect of MFSD1 or secondary to lysosomal dysfunction is unclear\",\n        \"Single-lab finding not yet independently replicated\",\n        \"Molecular mechanism by which a transporter regulates integrin trafficking not defined\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Proteomic and genetic studies expanded the MFSD1–GLMP complex to include GIMAP5, showing that all three proteins are interdependent for expression and that loss of any one recapitulates lymphopenia, liver pathology, and lipid deposition—establishing a tripartite lysosomal complex essential for immune and metabolic homeostasis.\",\n      \"evidence\": \"ENU mutagenesis screen, germline knockout mouse models for Mfsd1/Glmp/Gimap5, mass spectrometry\",\n      \"pmids\": [\"38055739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether GIMAP5 modulates MFSD1 transport activity or acts independently downstream is unknown\",\n        \"The mechanism linking lysosomal dipeptide export to lymphocyte development is not defined\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Two independent studies converged to identify MFSD1 as a lysosomal dipeptide uniporter: untargeted and targeted metabolomics showed dipeptide accumulation in MFSD1-deficient lysosomes, electrophysiology and proteoliposome reconstitution demonstrated direct uniport of cationic, neutral, and anionic dipeptides, and cryo-EM of the MFSD1–GLMP heterodimer in the outward-open state revealed the structural basis for dipeptide binding and selectivity.\",\n      \"evidence\": \"Cryo-EM structure, proteoliposome reconstitution, Xenopus oocyte electrophysiology, whole-cell patch-clamp in HEK293 cells, untargeted and targeted metabolomics, molecular dynamics simulations\",\n      \"pmids\": [\"38839979\", \"38507452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Inward-open and occluded conformational states have not been resolved structurally\",\n        \"Physiological regulation of MFSD1 transport activity (e.g., by luminal pH, post-translational modifications) is undefined\",\n        \"Relative contributions of MFSD1 versus other peptide transporters (e.g., PQLC2, PHT1) to lysosomal peptide efflux are not quantified\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the full conformational cycle of MFSD1 during transport, whether GIMAP5 directly modulates transport function, the molecular basis connecting dipeptide export to integrin recycling and immune phenotypes, and whether MFSD1 mutations cause human disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No human Mendelian disease linked to MFSD1 mutations\",\n        \"Structural basis for the complete transport cycle remains incomplete\",\n        \"Causal pathway from dipeptide accumulation to lymphopenia and liver disease not delineated\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 1, 2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"complexes\": [\n      \"MFSD1–GLMP heterodimer\",\n      \"MFSD1–GLMP–GIMAP5 complex\"\n    ],\n    \"partners\": [\n      \"GLMP\",\n      \"GIMAP5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}