{"gene":"MFSD1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2019,"finding":"MFSD1 localizes to lysosomes via a dileucine-based sorting motif and is not N-glycosylated. MFSD1 physically interacts with GLMP (glycosylated lysosomal membrane protein), forming a tightly linked lysosomal membrane protein transporter complex. GLMP is essential for maintaining normal MFSD1 levels in lysosomes, and vice versa. Mfsd1 knockout mice develop splenomegaly and severe liver disease.","method":"Knockout mouse model, lysosome isolation, proteomics, co-immunoprecipitation, mutational analysis of sorting motif, glycosylation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (KO mice, lysosome proteomics, Co-IP, mutagenesis of sorting motif), replicated by subsequent studies","pmids":["31661432"],"is_preprint":false},{"year":2023,"finding":"MFSD1 forms a protein complex with both GLMP and GIMAP5 (GTPase of immunity-associated protein 5). The interactions of MFSD1 and GLMP with GIMAP5 are essential for maintaining 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.","method":"ENU mutagenesis screen, germline knockout mice, proteomic analysis of MFSD1-associated proteins, phenotypic characterization of Mfsd1/Glmp/Gimap5 knockout mice","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — proteomic identification of complex, validated by multiple independent knockout lines with concordant phenotypes","pmids":["38055739"],"is_preprint":false},{"year":2024,"finding":"MFSD1, in complex with GLMP, functions as a general lysosomal dipeptide uniporter that exports cationic, neutral, and anionic dipeptides. Untargeted metabolomics of MFSD1-deficient mouse lysosomes revealed accumulation of cationic dipeptides. Cryo-EM structure of the dipeptide-bound MFSD1-GLMP complex in outward-open conformation characterized the heterodimer interface and substrate selectivity. Molecular dynamics simulations provided a structural basis for dipeptide selectivity.","method":"Untargeted metabolomics of isolated lysosomes, purified protein dipeptide binding assays, electrophysiology in Xenopus oocytes, isotope tracer studies, fluorescence-based transport assays in proteoliposomes, cryo-EM structure determination, molecular dynamics simulations","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure, reconstitution in proteoliposomes, electrophysiology, metabolomics, and MD simulations, all in a single rigorous study","pmids":["38839979"],"is_preprint":false},{"year":2024,"finding":"MFSD1 acts as a highly selective lysosomal uniporter for dipeptides containing lysine, arginine, or histidine residues. Targeted metabolomics showed accumulation of cationic dipeptides in MFSD1-deficient lysosomes. Whole-cell patch-clamp electrophysiology of HEK293 cells expressing MFSD1 at the cell surface showed transport affinities in the lower mM range for positively charged dipeptides. Single amino acids, tripeptides, and negatively charged dipeptides were not transported.","method":"Targeted metabolomics of MFSD1-deficient lysosomes, 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 / Moderate — direct electrophysiological transport assay combined with metabolomics, two orthogonal methods in a single study","pmids":["38507452"],"is_preprint":false},{"year":2019,"finding":"The Drosophila MFSD1 ortholog (Minerva) regulates O-glycosylation (specifically T-antigen levels) on a subset of proteins in macrophages to enable tissue invasion. Human MFSD1 rescues the minerva mutant's migration and T-antigen glycosylation defects, establishing functional conservation. Minerva/MFSD1 promotes T-antigen display most strongly on the sulfhydryl oxidase Qsox1, which is required for macrophage tissue entry.","method":"Drosophila genetic mutant rescue with human MFSD1, O-glycoproteomics, loss-of-function phenotypic analysis of macrophage migration","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional rescue by human MFSD1 in Drosophila, glycoproteomics, but mechanistic detail on how MFSD1 directly regulates glycosylation is not fully defined","pmids":["30910009"],"is_preprint":false},{"year":2022,"finding":"MFSD1 promotes recycling of endocytosed inactive β1 integrin 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 greater tumor cell migration and metastasis in mouse models.","method":"MFSD1 knockout tumor cells and mouse metastasis models (experimental and spontaneous), integrin recycling assays, focal adhesion turnover measurements, integrin activation index quantification","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO cells and in vivo models with defined cellular phenotype (integrin recycling, focal adhesion), single lab with multiple readouts","pmids":["35211397"],"is_preprint":false},{"year":2016,"finding":"MFSD1 protein localizes along the plasma membrane in neurons, and its expression is upregulated in mouse embryonic primary cortex cells upon amino acid deprivation, suggesting a nutrient-sensing role. Homology modelling predicts 12 transmembrane regions consistent with MFS transporter topology.","method":"Immunofluorescence/protein staining in neurons, amino acid starvation of primary cortex cells with mRNA quantification, homology modelling","journal":"Journal of molecular neuroscience : MN","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, protein localization by staining and expression change by starvation, no direct transport or functional assay","pmids":["27981419"],"is_preprint":false}],"current_model":"MFSD1 is a lysosomal membrane protein of the major facilitator superfamily that forms a tight heterodimeric complex with its accessory subunit GLMP (and additionally associates with GIMAP5); the MFSD1-GLMP complex functions as a general uniporter that exports dipeptides—products of lysosomal proteolysis—from the lysosomal lumen to the cytoplasm, with cryo-EM structure and electrophysiology defining its outward-open conformation and dipeptide selectivity; loss of MFSD1 causes lysosomal dipeptide accumulation, liver disease, splenomegaly, and lymphopenia in mice, and at the cellular level MFSD1 also promotes recycling of inactive β1 integrin to suppress tumor cell migration."},"narrative":{"mechanistic_narrative":"MFSD1 is a non-glycosylated lysosomal membrane protein of the major facilitator superfamily that functions as a general uniporter exporting dipeptides—the products of lysosomal proteolysis—from the lysosomal lumen to the cytoplasm [PMID:31661432, PMID:38839979]. It is delivered to lysosomes via a dileucine-based sorting motif and forms a tightly linked, mutually stabilizing complex with the accessory subunit GLMP, each protein being required to maintain the other's lysosomal levels [PMID:31661432]; the complex additionally associates with GIMAP5, whose stability depends on MFSD1/GLMP and which is critical for lymphocyte development and liver homeostasis [PMID:38055739]. A cryo-EM structure of the dipeptide-bound MFSD1-GLMP heterodimer in an outward-open conformation, together with proteoliposome reconstitution and electrophysiology, defines the heterodimer interface and a selectivity for cationic, neutral, and anionic dipeptides, with strongest transport of dipeptides containing lysine, arginine, or histidine and exclusion of single amino acids and tripeptides [PMID:38839979, PMID:38507452]. Loss of MFSD1 causes lysosomal accumulation of cationic dipeptides and produces splenomegaly, severe liver disease, lymphopenia, and extramedullary hematopoiesis in mice [PMID:31661432, PMID:38055739, PMID:38507452]. Beyond its lysosomal transport role, MFSD1 also promotes recycling of endocytosed inactive β1 integrin to suppress integrin activation and tumor cell migration [PMID:35211397].","teleology":[{"year":2019,"claim":"Establishing where MFSD1 resides and with whom it partners was the first step toward assigning function; this showed MFSD1 is a lysosomal MFS protein in an obligate complex with GLMP whose loss causes organ disease.","evidence":"Knockout mice, lysosome proteomics, Co-IP, and sorting-motif mutagenesis","pmids":["31661432"],"confidence":"High","gaps":["Did not identify the transported substrate","Mechanism linking complex loss to liver disease unresolved"]},{"year":2023,"claim":"Extending the complex membership clarified why MFSD1 loss causes immune and hepatic pathology by showing MFSD1 and GLMP stabilize GIMAP5, linking the transporter to lymphocyte development.","evidence":"ENU mutagenesis screen, germline knockouts of Mfsd1/Glmp/Gimap5, and proteomics of MFSD1-associated proteins","pmids":["38055739"],"confidence":"High","gaps":["Does not explain how GIMAP5 stabilization mechanistically requires transport activity","Direct binding topology of the tripartite complex not resolved"]},{"year":2024,"claim":"The long-standing question of MFSD1's substrate and transport mechanism was answered by defining the MFSD1-GLMP complex as a dipeptide uniporter with a structurally resolved selectivity filter.","evidence":"Untargeted/targeted lysosomal metabolomics, proteoliposome transport assays, Xenopus oocyte and HEK293 patch-clamp electrophysiology, and cryo-EM of the dipeptide-bound outward-open complex with MD simulations","pmids":["38839979","38507452"],"confidence":"High","gaps":["Conformational cycle beyond the outward-open state not captured","Physiological consequence of dipeptide export for downstream metabolism not traced"]},{"year":2022,"claim":"A distinct cellular role was uncovered, implicating MFSD1 in membrane trafficking by showing it recycles inactive β1 integrin and thereby restrains tumor cell migration.","evidence":"MFSD1 knockout tumor cells, integrin recycling and focal-adhesion turnover assays, and mouse metastasis models","pmids":["35211397"],"confidence":"Medium","gaps":["Single lab; reciprocal validation limited","Relationship between lysosomal dipeptide transport and integrin recycling not established"]},{"year":2019,"claim":"A conserved organismal role was indicated by demonstrating that the Drosophila ortholog regulates protein O-glycosylation for macrophage tissue invasion, with human MFSD1 rescuing the defect.","evidence":"Drosophila mutant rescue with human MFSD1, O-glycoproteomics, and macrophage migration phenotyping","pmids":["30910009"],"confidence":"Medium","gaps":["How a lysosomal dipeptide transporter influences glycosylation is undefined","Direct versus indirect effect on T-antigen display unresolved"]},{"year":null,"claim":"How MFSD1's defined dipeptide-export activity mechanistically connects to GIMAP5 stabilization, β1 integrin recycling, and conserved glycosylation effects remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No mechanism unifying transport activity with trafficking and immune phenotypes","Full transport cycle conformations not resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[2,3]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,2,3]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[2,3]}],"complexes":["MFSD1-GLMP heterodimer","MFSD1-GLMP-GIMAP5 complex"],"partners":["GLMP","GIMAP5"],"other_free_text":[]}},"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":"35127371","id":"PMC_35127371","title":"Therapeutic regulation of autophagy in hepatic metabolism.","date":"2021","source":"Acta pharmaceutica Sinica. B","url":"https://pubmed.ncbi.nlm.nih.gov/35127371","citation_count":121,"is_preprint":false},{"pmid":"28878041","id":"PMC_28878041","title":"Characteristics of 29 novel atypical solute carriers of major facilitator superfamily type: evolutionary conservation, predicted structure and neuronal co-expression.","date":"2017","source":"Open biology","url":"https://pubmed.ncbi.nlm.nih.gov/28878041","citation_count":44,"is_preprint":false},{"pmid":"21044875","id":"PMC_21044875","title":"Long evolutionary conservation and considerable tissue specificity of several atypical solute carrier transporters.","date":"2010","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/21044875","citation_count":43,"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":"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":"30910009","id":"PMC_30910009","title":"A conserved major facilitator superfamily member orchestrates a subset of O-glycosylation to aid macrophage tissue invasion.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/30910009","citation_count":20,"is_preprint":false},{"pmid":"36324662","id":"PMC_36324662","title":"Genome-wide by Environment Interaction Study of Stressful Life Events and Hospital-Treated Depression in the iPSYCH2012 Sample.","date":"2021","source":"Biological psychiatry global open 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MFSD1 physically interacts with GLMP (glycosylated lysosomal membrane protein), forming a tightly linked lysosomal membrane protein transporter complex. GLMP is essential for maintaining normal MFSD1 levels in lysosomes, and vice versa. Mfsd1 knockout mice develop splenomegaly and severe liver disease.\",\n      \"method\": \"Knockout mouse model, lysosome isolation, proteomics, co-immunoprecipitation, mutational analysis of sorting motif, glycosylation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (KO mice, lysosome proteomics, Co-IP, mutagenesis of sorting motif), replicated by subsequent studies\",\n      \"pmids\": [\"31661432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MFSD1 forms a protein complex with both GLMP and GIMAP5 (GTPase of immunity-associated protein 5). The interactions of MFSD1 and GLMP with GIMAP5 are essential for maintaining 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.\",\n      \"method\": \"ENU mutagenesis screen, germline knockout mice, proteomic analysis of MFSD1-associated proteins, phenotypic characterization of Mfsd1/Glmp/Gimap5 knockout mice\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — proteomic identification of complex, validated by multiple independent knockout lines with concordant phenotypes\",\n      \"pmids\": [\"38055739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MFSD1, in complex with GLMP, functions as a general lysosomal dipeptide uniporter that exports cationic, neutral, and anionic dipeptides. Untargeted metabolomics of MFSD1-deficient mouse lysosomes revealed accumulation of cationic dipeptides. Cryo-EM structure of the dipeptide-bound MFSD1-GLMP complex in outward-open conformation characterized the heterodimer interface and substrate selectivity. Molecular dynamics simulations provided a structural basis for dipeptide selectivity.\",\n      \"method\": \"Untargeted metabolomics of isolated lysosomes, purified protein dipeptide binding assays, electrophysiology in Xenopus oocytes, isotope tracer studies, fluorescence-based transport assays in proteoliposomes, cryo-EM structure determination, molecular dynamics simulations\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure, reconstitution in proteoliposomes, electrophysiology, metabolomics, and MD simulations, all in a single rigorous study\",\n      \"pmids\": [\"38839979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MFSD1 acts as a highly selective lysosomal uniporter for dipeptides containing lysine, arginine, or histidine residues. Targeted metabolomics showed accumulation of cationic dipeptides in MFSD1-deficient lysosomes. Whole-cell patch-clamp electrophysiology of HEK293 cells expressing MFSD1 at the cell surface showed transport affinities in the lower mM range for positively charged dipeptides. Single amino acids, tripeptides, and negatively charged dipeptides were not transported.\",\n      \"method\": \"Targeted metabolomics of MFSD1-deficient lysosomes, 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 / Moderate — direct electrophysiological transport assay combined with metabolomics, two orthogonal methods in a single study\",\n      \"pmids\": [\"38507452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The Drosophila MFSD1 ortholog (Minerva) regulates O-glycosylation (specifically T-antigen levels) on a subset of proteins in macrophages to enable tissue invasion. Human MFSD1 rescues the minerva mutant's migration and T-antigen glycosylation defects, establishing functional conservation. Minerva/MFSD1 promotes T-antigen display most strongly on the sulfhydryl oxidase Qsox1, which is required for macrophage tissue entry.\",\n      \"method\": \"Drosophila genetic mutant rescue with human MFSD1, O-glycoproteomics, loss-of-function phenotypic analysis of macrophage migration\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional rescue by human MFSD1 in Drosophila, glycoproteomics, but mechanistic detail on how MFSD1 directly regulates glycosylation is not fully defined\",\n      \"pmids\": [\"30910009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MFSD1 promotes recycling of endocytosed inactive β1 integrin 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 greater tumor cell migration and metastasis in mouse models.\",\n      \"method\": \"MFSD1 knockout tumor cells and mouse metastasis models (experimental and spontaneous), integrin recycling assays, focal adhesion turnover measurements, integrin activation index quantification\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO cells and in vivo models with defined cellular phenotype (integrin recycling, focal adhesion), single lab with multiple readouts\",\n      \"pmids\": [\"35211397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"MFSD1 protein localizes along the plasma membrane in neurons, and its expression is upregulated in mouse embryonic primary cortex cells upon amino acid deprivation, suggesting a nutrient-sensing role. Homology modelling predicts 12 transmembrane regions consistent with MFS transporter topology.\",\n      \"method\": \"Immunofluorescence/protein staining in neurons, amino acid starvation of primary cortex cells with mRNA quantification, homology modelling\",\n      \"journal\": \"Journal of molecular neuroscience : MN\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, protein localization by staining and expression change by starvation, no direct transport or functional assay\",\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 heterodimeric complex with its accessory subunit GLMP (and additionally associates with GIMAP5); the MFSD1-GLMP complex functions as a general uniporter that exports dipeptides—products of lysosomal proteolysis—from the lysosomal lumen to the cytoplasm, with cryo-EM structure and electrophysiology defining its outward-open conformation and dipeptide selectivity; loss of MFSD1 causes lysosomal dipeptide accumulation, liver disease, splenomegaly, and lymphopenia in mice, and at the cellular level MFSD1 also promotes recycling of inactive β1 integrin to suppress tumor cell migration.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MFSD1 is a non-glycosylated lysosomal membrane protein of the major facilitator superfamily that functions as a general uniporter exporting dipeptides—the products of lysosomal proteolysis—from the lysosomal lumen to the cytoplasm [#0, #2]. It is delivered to lysosomes via a dileucine-based sorting motif and forms a tightly linked, mutually stabilizing complex with the accessory subunit GLMP, each protein being required to maintain the other's lysosomal levels [#0]; the complex additionally associates with GIMAP5, whose stability depends on MFSD1/GLMP and which is critical for lymphocyte development and liver homeostasis [#1]. A cryo-EM structure of the dipeptide-bound MFSD1-GLMP heterodimer in an outward-open conformation, together with proteoliposome reconstitution and electrophysiology, defines the heterodimer interface and a selectivity for cationic, neutral, and anionic dipeptides, with strongest transport of dipeptides containing lysine, arginine, or histidine and exclusion of single amino acids and tripeptides [#2, #3]. Loss of MFSD1 causes lysosomal accumulation of cationic dipeptides and produces splenomegaly, severe liver disease, lymphopenia, and extramedullary hematopoiesis in mice [#0, #1, #3]. Beyond its lysosomal transport role, MFSD1 also promotes recycling of endocytosed inactive β1 integrin to suppress integrin activation and tumor cell migration [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2019,\n      \"claim\": \"Establishing where MFSD1 resides and with whom it partners was the first step toward assigning function; this showed MFSD1 is a lysosomal MFS protein in an obligate complex with GLMP whose loss causes organ disease.\",\n      \"evidence\": \"Knockout mice, lysosome proteomics, Co-IP, and sorting-motif mutagenesis\",\n      \"pmids\": [\"31661432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the transported substrate\", \"Mechanism linking complex loss to liver disease unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extending the complex membership clarified why MFSD1 loss causes immune and hepatic pathology by showing MFSD1 and GLMP stabilize GIMAP5, linking the transporter to lymphocyte development.\",\n      \"evidence\": \"ENU mutagenesis screen, germline knockouts of Mfsd1/Glmp/Gimap5, and proteomics of MFSD1-associated proteins\",\n      \"pmids\": [\"38055739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not explain how GIMAP5 stabilization mechanistically requires transport activity\", \"Direct binding topology of the tripartite complex not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The long-standing question of MFSD1's substrate and transport mechanism was answered by defining the MFSD1-GLMP complex as a dipeptide uniporter with a structurally resolved selectivity filter.\",\n      \"evidence\": \"Untargeted/targeted lysosomal metabolomics, proteoliposome transport assays, Xenopus oocyte and HEK293 patch-clamp electrophysiology, and cryo-EM of the dipeptide-bound outward-open complex with MD simulations\",\n      \"pmids\": [\"38839979\", \"38507452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational cycle beyond the outward-open state not captured\", \"Physiological consequence of dipeptide export for downstream metabolism not traced\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A distinct cellular role was uncovered, implicating MFSD1 in membrane trafficking by showing it recycles inactive β1 integrin and thereby restrains tumor cell migration.\",\n      \"evidence\": \"MFSD1 knockout tumor cells, integrin recycling and focal-adhesion turnover assays, and mouse metastasis models\",\n      \"pmids\": [\"35211397\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; reciprocal validation limited\", \"Relationship between lysosomal dipeptide transport and integrin recycling not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"A conserved organismal role was indicated by demonstrating that the Drosophila ortholog regulates protein O-glycosylation for macrophage tissue invasion, with human MFSD1 rescuing the defect.\",\n      \"evidence\": \"Drosophila mutant rescue with human MFSD1, O-glycoproteomics, and macrophage migration phenotyping\",\n      \"pmids\": [\"30910009\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a lysosomal dipeptide transporter influences glycosylation is undefined\", \"Direct versus indirect effect on T-antigen display unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MFSD1's defined dipeptide-export activity mechanistically connects to GIMAP5 stabilization, β1 integrin recycling, and conserved glycosylation effects remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No mechanism unifying transport activity with trafficking and immune phenotypes\", \"Full transport cycle conformations not resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"complexes\": [\"MFSD1-GLMP heterodimer\", \"MFSD1-GLMP-GIMAP5 complex\"],\n    \"partners\": [\"GLMP\", \"GIMAP5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}