{"gene":"SPART","run_date":"2026-06-10T07:46:39","timeline":{"discoveries":[{"year":2002,"finding":"SPG20 encodes spartin, which by comparative sequence analysis shares similarity with molecules involved in endosomal trafficking and with spastin (a microtubule-interacting HSP protein); a frameshift mutation in SPG20 causes Troyer syndrome.","method":"Genetic mapping, sequencing, and comparative sequence analysis","journal":"Nature genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — sequence analysis and genetic mapping; functional inference from homology, not direct biochemical experiment, but replicated across subsequent studies","pmids":["12134148"],"is_preprint":false},{"year":2005,"finding":"Spartin (SPG20) interacts with Eps15, a protein involved in endocytosis and cell proliferation; spartin is both cytosolic and membrane-associated.","method":"Yeast two-hybrid screen of adult human brain library, fusion protein pulldown, cellular redistribution assay, anti-spartin antibody fractionation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid confirmed by pulldown and redistribution assay, single lab, no reciprocal Co-IP","pmids":["16036216"],"is_preprint":false},{"year":2009,"finding":"Spartin associates with lipid droplet surfaces and regulates lipid droplet size and number; it binds TIP47 and competes with adipophilin for LD occupancy; WWP1 (AIP5) binds spartin, transfers ubiquitin to it, removes it from LDs, and reduces its levels. The Troyer syndrome truncation mutant lacks these activities.","method":"Co-IP, RNA interference knockdown, overexpression, lipid droplet imaging, ubiquitination assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, RNAi, imaging, ubiquitination assay) in single lab, findings replicated in subsequent studies","pmids":["19307600"],"is_preprint":false},{"year":2009,"finding":"Endogenous spartin localizes to a cytosolic pool that is recruited to endosomes and lipid droplets; cytosolic spartin is mono-ubiquitinated; spartin interacts via a PPXY motif with ubiquitin E3 ligases AIP4 (ITCH) and AIP5 (WWP1); the PPXY motif and these ligases are not required for spartin's own ubiquitination, suggesting spartin acts as an adaptor.","method":"Subcellular fractionation, immunofluorescence, endogenous protein immunoprecipitation, PPXY motif mutagenesis","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous protein biochemistry, mutagenesis of PPXY motif, orthogonal to PMID 19307600 findings, consistent across two independent labs","pmids":["19580544"],"is_preprint":false},{"year":2010,"finding":"The spartin MIT domain binds ESCRT-III protein IST1 with micromolar affinity (but not CHMP1-7); spartin co-localizes with IST1 at the midbody; IST1 depletion reduces spartin at midbodies; spartin depletion impairs cytokinesis; a structure-based F24D mutation in the MIT domain blocks the spartin–IST1 interaction, prevents midbody localization, and acts dominant-negatively to impair cytokinesis.","method":"Yeast two-hybrid, in vitro surface plasmon resonance, siRNA knockdown, immunofluorescence co-localization, dominant-negative mutation (F24D)","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — SPR binding kinetics, structure-based mutagenesis, siRNA phenotype, multiple orthogonal methods in one study","pmids":["20719964"],"is_preprint":false},{"year":2011,"finding":"The plant-related senescence (PRS) domain of spartin interacts specifically with cardiolipin but not phosphatidylcholine or phosphatidylethanolamine; spartin knockdown depolarizes mitochondrial membrane potential and significantly decreases mitochondrial calcium uptake.","method":"Lipid-binding assay with purified PRS domain, siRNA knockdown in neuroblastoma cells, mitochondrial membrane potential measurements, mitochondrial calcium uptake assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct lipid-binding assay with domain construct plus functional siRNA readouts, single lab","pmids":["21559443"],"is_preprint":false},{"year":2011,"finding":"SPG20 promoter hypermethylation silences spartin expression; spartin depletion in cancer cells causes cytokinesis arrest, reversed by inhibiting SPG20 methylation.","method":"Methylation-specific PCR, qRT-PCR, siRNA knockdown, cell cycle analysis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional reversal of cytokinesis arrest by methylation inhibition provides mechanistic link, single lab","pmids":["21499309"],"is_preprint":false},{"year":2012,"finding":"Spg20-/- mice show: (1) impaired cytokinesis in embryonic fibroblasts and binucleated chondrocytes in bone growth plates; (2) increased axon branching in cortical neurons reversed by reintroduction of spartin requiring its IST1 interaction; (3) elevated BMP/Smad1/5 phosphorylation in fibroblasts suggesting altered BMP receptor trafficking; (4) increased lipid droplet numbers and altered perilipin levels in adipose tissue.","method":"Spg20 knockout mice, primary neuronal culture, primary fibroblast culture, immunofluorescence, Western blot, rescue with wild-type spartin","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout model with multiple orthogonal cellular readouts and rescue experiments confirming mechanistic requirements","pmids":["22619377"],"is_preprint":false},{"year":2019,"finding":"SPART loss-of-function leads to decreased mitochondrial complex I (NADH dehydrogenase) activity, decreased ATP synthesis, defective mitochondrial membrane potential, increased ROS, and altered intracellular Ca2+ homeostasis; re-expression of wild-type spartin restores Ca2+ homeostasis.","method":"SH-SY5Y cell model with SPART frameshift mutation, enzymatic complex I activity assay, ATP synthesis assay, mitochondrial membrane potential measurement, ROS detection, Ca2+ imaging, wild-type rescue","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays with rescue, single lab, consistent with prior findings from PMID 21559443","pmids":["31314595"],"is_preprint":false},{"year":2018,"finding":"Knockout of SPG20/spartin activates the EGFR/MAPK signaling pathway to promote cell proliferation; EGFR kinase or ERK1/2 inhibitors rescue the proliferation phenotype caused by spartin loss.","method":"SPG20 knockout cells, in vitro proliferation assays, colony formation, Western blot for pathway activation, pharmacological inhibition with EGFR and ERK1/2 inhibitors, in vivo xenografts","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway placement by pharmacological rescue, single lab, two orthogonal approaches (inhibitors + knockout)","pmids":["29673586"],"is_preprint":false},{"year":2023,"finding":"Mutant SPART causes impaired mitochondrial import of nuclear-encoded proteins, leading to significant decrease of CoQ10 biosynthesis enzymes COQ7 and COQ9 and severe reduction in CoQ content; CoQ supplementation restores cellular ATP levels to the same extent as re-expression of wild-type SPART.","method":"Patient-derived fibroblasts, mitochondrial protein import assay, mass spectrometry proteomics, CoQ content measurement, ATP assay, wild-type SPART rescue","journal":"Open biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mitochondrial import assay with two cell models and CoQ rescue, single lab, multiple orthogonal methods","pmids":["37433530"],"is_preprint":false},{"year":2024,"finding":"SPG20 detects lipid-packing defects in damaged lysosomal membranes via sensory amphipathic helices before membrane rupture; SPG20 binds IST1 on damaged lysosomes and, when lipid-packing defects are extensive (e.g., during lipid peroxidation), recruits and activates ITCH to mark the lysosome with K63-linked ubiquitin chains, initiating lysophagy.","method":"Human cell-based assays, lysosomal damage assays (LLOMe), co-immunoprecipitation, ubiquitin linkage-specific antibodies, SPG20 amphipathic helix mutagenesis, IST1 binding assays, ITCH recruitment assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, mutagenesis of amphipathic helices, ubiquitin chain typing, functional lysophagy assay) in a single rigorous study","pmids":["38503285"],"is_preprint":false},{"year":2025,"finding":"HCV NS3/4A protease cleaves SPG20 at Cys504 and Cys562; cleavage disrupts SPG20–TIP47 interaction and prevents ITCH recruitment to LD-associated ADRP/adipophilin, thereby blocking ubiquitin-dependent ADRP degradation and promoting large lipid droplet formation.","method":"Immunoblot of HCV-infected cells, NS3/4A transfection (active vs. inactive mutant), site-directed mutagenesis of cleavage sites, co-immunoprecipitation of SPG20 with TIP47, siRNA knockdown of ITCH, immunofluorescence","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — site-directed mutagenesis identifying specific cleavage sites, active-site inactive mutant controls, Co-IP, siRNA rescue, single lab with multiple orthogonal methods","pmids":["40985721"],"is_preprint":false},{"year":2026,"finding":"SPART interacts with and disrupts the endosomal localization of ITCH E3-ubiquitin ligase; ITCH ubiquitinates the ZIKV capsid to trigger viral uncoating; loss of SPART enhances ZIKV replication through an ITCH-dependent mechanism (effect absent in SPART-ITCH double knockouts), establishing SPART as a pan-orthoflavivirus restriction factor acting via ITCH-mediated capsid ubiquitination.","method":"Genome-wide CRISPR activation screen, SPART/ITCH single and double knockout cell lines, Spg20-/- and Itch-/- mice infected with ZIKV, viral replication assays, ITCH localization imaging, ubiquitination assays on viral capsid","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR screen validated by double-knockout epistasis in cells and in vivo mouse models, multiple orthogonal methods across cell and animal systems","pmids":["42161262"],"is_preprint":false}],"current_model":"Spartin (SPART/SPG20) is a multifunctional scaffold protein with an N-terminal MIT domain that binds ESCRT-III protein IST1 to enable midbody localization and cytokinesis, a C-terminal plant-related senescence domain that binds cardiolipin and regulates mitochondrial membrane potential, Ca2+ homeostasis, and nuclear-encoded mitochondrial protein import (including CoQ biosynthesis enzymes); at lipid droplets, spartin binds TIP47 and recruits/activates the HECT E3 ubiquitin ligase ITCH to ubiquitinate and degrade the LD-coat protein ADRP/adipophilin, thereby driving LD turnover; on damaged lysosomes, spartin detects lipid-packing defects via sensory amphipathic helices, binds IST1, and activates ITCH to deposit K63-linked ubiquitin chains that initiate lysophagy; and in innate antiviral defense, spartin restricts orthoflavivirus replication by sequestering ITCH away from endosomes, thereby enabling ITCH-mediated ubiquitination of viral capsid and uncoating."},"narrative":{"mechanistic_narrative":"Spartin (SPART/SPG20) is a multifunctional adaptor protein that couples membrane and organelle quality control to the ubiquitin system, and its loss causes the autosomal recessive hereditary spastic paraplegia Troyer syndrome [PMID:12134148]. Through its N-terminal MIT domain it binds the ESCRT-III protein IST1 with micromolar affinity, an interaction required for spartin's recruitment to the midbody and for completion of cytokinesis; a structure-based MIT mutation that abolishes IST1 binding blocks midbody localization and acts dominant-negatively [PMID:20719964]. A central feature of spartin function is its role as a recruitment platform for HECT-family E3 ubiquitin ligases ITCH (AIP4) and WWP1 (AIP5), which it engages via a PPXY motif while itself acting as an adaptor rather than an obligate substrate [PMID:19580544]. At lipid droplets, spartin binds TIP47, competes with adipophilin for droplet occupancy, and controls lipid droplet size and number through ITCH/WWP1-dependent ubiquitination [PMID:19307600]. On damaged lysosomes, spartin senses lipid-packing defects through amphipathic helices, binds IST1, and recruits and activates ITCH to deposit K63-linked ubiquitin chains that initiate lysophagy [PMID:38503285]. The same ITCH-targeting activity underlies antiviral restriction: spartin redistributes ITCH away from endosomes to enable ITCH-mediated ubiquitination of the orthoflavivirus capsid and viral uncoating, establishing spartin as a pan-orthoflavivirus restriction factor [PMID:42161262]. Independently, its C-terminal plant-related senescence domain binds cardiolipin and supports mitochondrial membrane potential, calcium uptake, complex I activity, and nuclear-encoded mitochondrial protein import, including the CoQ biosynthetic enzymes COQ7 and COQ9 [PMID:21559443, PMID:31314595, PMID:37433530]. In vivo, Spg20-deficient mice recapitulate impaired cytokinesis, increased neuronal axon branching reversed by IST1-binding-competent spartin, and lipid droplet accumulation [PMID:22619377].","teleology":[{"year":2002,"claim":"Established the gene-disease link and first functional context: a frameshift mutation in SPG20 causes Troyer syndrome, with sequence similarity to endosomal trafficking and spastin-like HSP proteins pointing toward membrane biology.","evidence":"Genetic mapping, sequencing, and comparative sequence analysis in Troyer syndrome families","pmids":["12134148"],"confidence":"Medium","gaps":["Function inferred from homology rather than biochemistry","No direct demonstration of trafficking activity"]},{"year":2005,"claim":"Provided the first direct interaction partner, linking spartin to endocytic machinery and showing it has both cytosolic and membrane-associated pools.","evidence":"Yeast two-hybrid of human brain library with pulldown and redistribution validation","pmids":["16036216"],"confidence":"Medium","gaps":["No reciprocal Co-IP","Functional consequence of Eps15 interaction not established"]},{"year":2009,"claim":"Defined spartin as a lipid-droplet regulator and an adaptor for HECT E3 ligases, showing it binds TIP47, competes with adipophilin, and engages ITCH/WWP1 via a PPXY motif while acting as an adaptor rather than obligate substrate.","evidence":"Co-IP, RNAi, LD imaging, ubiquitination assays, and PPXY mutagenesis on endogenous protein across two labs","pmids":["19307600","19580544"],"confidence":"High","gaps":["Identity of ITCH/WWP1 substrates at LDs not yet defined","How spartin selects between the two ligases unclear"]},{"year":2010,"claim":"Resolved the mechanism of spartin's role in cell division: the MIT domain binds ESCRT-III IST1 to target spartin to the midbody and complete cytokinesis.","evidence":"SPR binding kinetics, structure-based F24D mutagenesis, siRNA, and co-localization imaging","pmids":["20719964"],"confidence":"High","gaps":["Downstream effector of midbody spartin not defined","Relationship between MIT/IST1 axis and the LD/ligase functions unresolved"]},{"year":2011,"claim":"Identified a distinct mitochondrial function: the PRS domain binds cardiolipin, and spartin loss depolarizes mitochondria and impairs calcium uptake, separating membrane lipid sensing from the MIT/ESCRT activity.","evidence":"Lipid-binding assay with purified PRS domain plus siRNA functional readouts in neuroblastoma","pmids":["21559443"],"confidence":"Medium","gaps":["Single lab","Mechanistic link between cardiolipin binding and membrane potential not delineated"]},{"year":2011,"claim":"Showed that epigenetic silencing of SPG20 by promoter hypermethylation phenocopies depletion, causing cytokinesis arrest reversible by demethylation, tying spartin loss to a cancer-relevant proliferation defect.","evidence":"Methylation-specific PCR, siRNA, and cell-cycle analysis with methylation-inhibition rescue","pmids":["21499309"],"confidence":"Medium","gaps":["Does not establish direct oncogenic mechanism","Single lab"]},{"year":2012,"claim":"Validated multiple spartin functions in vivo and established that the IST1 interaction is required to restrain neuronal axon branching, integrating cytokinesis, neuronal, BMP-signaling, and lipid-droplet phenotypes in a knockout animal.","evidence":"Spg20-/- mice with primary neuronal/fibroblast culture, imaging, Western blot, and spartin rescue","pmids":["22619377"],"confidence":"High","gaps":["BMP/Smad effect attributed to altered receptor trafficking but mechanism not resolved","Adipose LD phenotype not linked to specific ligase activity"]},{"year":2018,"claim":"Placed spartin loss upstream of EGFR/MAPK signaling, showing knockout activates this pathway to drive proliferation reversible by EGFR or ERK1/2 inhibition.","evidence":"SPG20 knockout cells, proliferation/colony assays, pathway Westerns, pharmacological rescue, and xenografts","pmids":["29673586"],"confidence":"Medium","gaps":["Direct molecular link between spartin and EGFR not defined","Single lab"]},{"year":2019,"claim":"Deepened the mitochondrial phenotype, showing SPART loss reduces complex I activity and ATP synthesis, increases ROS, and disrupts Ca2+ homeostasis, with rescue restoring calcium handling.","evidence":"SH-SY5Y SPART frameshift model with complex I, ATP, membrane potential, ROS, Ca2+ assays and rescue","pmids":["31314595"],"confidence":"Medium","gaps":["Whether mitochondrial defects are primary or secondary to import failure not resolved","Single lab"]},{"year":2023,"claim":"Provided a mechanistic basis for the mitochondrial bioenergetic defect: mutant SPART impairs import of nuclear-encoded proteins including COQ7/COQ9, depleting CoQ, with CoQ supplementation restoring ATP comparably to wild-type rescue.","evidence":"Patient fibroblasts, mitochondrial import assay, MS proteomics, CoQ measurement, ATP assay, rescue","pmids":["37433530"],"confidence":"Medium","gaps":["How spartin supports the import machinery mechanistically unknown","Single lab"]},{"year":2024,"claim":"Unified spartin's membrane-sensing and ligase-recruitment functions in lysophagy: amphipathic helices detect lipid-packing defects on damaged lysosomes, and spartin binds IST1 and activates ITCH to deposit K63 ubiquitin chains initiating lysosomal autophagy.","evidence":"Cell-based LLOMe damage assays, Co-IP, ubiquitin linkage typing, amphipathic helix mutagenesis, ITCH recruitment assays","pmids":["38503285"],"confidence":"High","gaps":["Identity of the ubiquitinated lysosomal substrate(s) not defined","Threshold determining ITCH activation not quantified"]},{"year":2025,"claim":"Demonstrated that a viral protease exploits the spartin-ITCH lipid-droplet pathway: HCV NS3/4A cleaves SPG20 at Cys504/Cys562, disrupting TIP47 binding and ITCH recruitment to block ADRP degradation and promote large LD formation.","evidence":"HCV infection/NS3-4A transfection, cleavage-site mutagenesis, Co-IP, ITCH siRNA, immunofluorescence","pmids":["40985721"],"confidence":"High","gaps":["Whether cleavage benefits viral replication directly not established here","Single lab"]},{"year":2026,"claim":"Established spartin as a pan-orthoflavivirus restriction factor, showing it sequesters ITCH from endosomes to enable ITCH ubiquitination of viral capsid and uncoating, with epistasis confirming an ITCH-dependent mechanism.","evidence":"Genome-wide CRISPRa screen, SPART/ITCH single and double knockouts, Spg20-/- and Itch-/- mice, viral assays, capsid ubiquitination","pmids":["42161262"],"confidence":"High","gaps":["How spartin spatially redistributes ITCH at the molecular level not detailed","Breadth across other virus families not tested"]},{"year":null,"claim":"It remains unresolved how spartin's distinct domain activities — MIT/IST1 targeting, PPXY-mediated E3 ligase recruitment, amphipathic membrane sensing, and PRS/cardiolipin-dependent mitochondrial support — are coordinated and which contributes to Troyer syndrome neuropathology.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model integrating the multiple domains","Tissue-specific determinant of motor-neuron vulnerability unknown","Direct ubiquitination substrates at each membrane site incompletely defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,11]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[5]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[11]}],"localization":[{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[2,3]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[11]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[5,8]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[4,6,7]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[11]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[13]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[3,2]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5,8,10]}],"complexes":[],"partners":["IST1","ITCH","WWP1","TIP47","EPS15"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8N0X7","full_name":"Spartin","aliases":["Spastic paraplegia 20 protein","Trans-activated by hepatitis C virus core protein 1"],"length_aa":666,"mass_kda":72.8,"function":"Lipophagy receptor that plays an important role in lipid droplet (LD) turnover in motor neurons (PubMed:37443287). Localizes to LDs and interacts with components of the autophagy machinery, such as MAP1LC3A/C proteins to deliver LDs to autophagosomes for degradation via lipophagy (PubMed:37443287). Lipid transfer protein required for lipid droplet degradation, including by lipophagy (PubMed:38190532). Can bind and transfer all lipid species found in lipid droplets, from phospholipids to triglycerides and sterol esters but the direction of lipid transfer by spartin and its cargos are unknown (PubMed:38190532). May be implicated in endosomal trafficking, or microtubule dynamics, or both. Participates in cytokinesis (PubMed:20719964)","subcellular_location":"Cytoplasm; Midbody; Lipid droplet","url":"https://www.uniprot.org/uniprotkb/Q8N0X7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPART","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CAPZB","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/search/SPART","total_profiled":1310},"omim":[{"mim_id":"607111","title":"SPARTIN; SPART","url":"https://www.omim.org/entry/607111"},{"mim_id":"604857","title":"SIGNAL RECOGNITION PARTICLE, 54-KD; SRP54","url":"https://www.omim.org/entry/604857"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SPART"},"hgnc":{"alias_symbol":["KIAA0610","TAHCCP1"],"prev_symbol":["SPG20"]},"alphafold":{"accession":"Q8N0X7","domains":[{"cath_id":"1.20.58.80","chopping":"10-101","consensus_level":"high","plddt":89.3596,"start":10,"end":101},{"cath_id":"2.30.29.30","chopping":"216-334","consensus_level":"high","plddt":80.1222,"start":216,"end":334},{"cath_id":"-","chopping":"419-512_539-625","consensus_level":"high","plddt":68.2348,"start":419,"end":625}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N0X7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N0X7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N0X7-F1-predicted_aligned_error_v6.png","plddt_mean":62.66},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPART","jax_strain_url":"https://www.jax.org/strain/search?query=SPART"},"sequence":{"accession":"Q8N0X7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8N0X7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8N0X7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N0X7"}},"corpus_meta":[{"pmid":"12134148","id":"PMC_12134148","title":"SPG20 is mutated in Troyer syndrome, an hereditary spastic paraplegia.","date":"2002","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12134148","citation_count":200,"is_preprint":false},{"pmid":"19307600","id":"PMC_19307600","title":"A role for ubiquitin ligases and Spartin/SPG20 in lipid droplet turnover.","date":"2009","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19307600","citation_count":117,"is_preprint":false},{"pmid":"20719964","id":"PMC_20719964","title":"SPG20 protein spartin is recruited to midbodies by ESCRT-III protein Ist1 and participates in cytokinesis.","date":"2010","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/20719964","citation_count":67,"is_preprint":false},{"pmid":"21499309","id":"PMC_21499309","title":"SPG20, a novel biomarker for early detection of colorectal cancer, encodes a regulator of cytokinesis.","date":"2011","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/21499309","citation_count":63,"is_preprint":false},{"pmid":"19580544","id":"PMC_19580544","title":"Endogenous spartin (SPG20) is recruited to endosomes and lipid droplets and interacts with the ubiquitin E3 ligases AIP4 and AIP5.","date":"2009","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/19580544","citation_count":61,"is_preprint":false},{"pmid":"38503285","id":"PMC_38503285","title":"Lysosomal damage sensing and lysophagy initiation by SPG20-ITCH.","date":"2024","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/38503285","citation_count":58,"is_preprint":false},{"pmid":"22619377","id":"PMC_22619377","title":"Spg20-/- mice reveal multimodal functions for Troyer syndrome protein spartin in lipid droplet maintenance, cytokinesis and BMP signaling.","date":"2012","source":"Human molecular 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of gastric cancer.","date":"2019","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/31194837","citation_count":14,"is_preprint":false},{"pmid":"26003402","id":"PMC_26003402","title":"Recurrent null mutation in SPG20 leads to Troyer syndrome.","date":"2015","source":"Molecular and cellular probes","url":"https://pubmed.ncbi.nlm.nih.gov/26003402","citation_count":12,"is_preprint":false},{"pmid":"34751409","id":"PMC_34751409","title":"KLF4, DAPK1 and SPG20 promoter methylation is not affected by DNMT1 silencing and hypomethylating drugs in lymphoma cells.","date":"2021","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/34751409","citation_count":11,"is_preprint":false},{"pmid":"34957998","id":"PMC_34957998","title":"Methylation of FBN1, SPG20, ITF2, RUNX3, SNCA, MLH1, and SEPT9 genes in circulating cell-free DNA as biomarkers of colorectal cancer.","date":"2022","source":"Cancer biomarkers : section A of Disease markers","url":"https://pubmed.ncbi.nlm.nih.gov/34957998","citation_count":11,"is_preprint":false},{"pmid":"28875386","id":"PMC_28875386","title":"Novel SPG20 mutation in an extended family with Troyer syndrome.","date":"2017","source":"Metabolic brain disease","url":"https://pubmed.ncbi.nlm.nih.gov/28875386","citation_count":10,"is_preprint":false},{"pmid":"31535723","id":"PMC_31535723","title":"Dwarfism in Troyer syndrome: a family with SPG20 compound heterozygous mutations and a literature review.","date":"2019","source":"Annals of the New York Academy of Sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31535723","citation_count":8,"is_preprint":false},{"pmid":"37433330","id":"PMC_37433330","title":"Mutant SPART causes defects in mitochondrial protein import and bioenergetics reversed by Coenzyme Q.","date":"2023","source":"Open biology","url":"https://pubmed.ncbi.nlm.nih.gov/37433330","citation_count":7,"is_preprint":false},{"pmid":"31109594","id":"PMC_31109594","title":"Aberrant methylation status of SPG20 promoter in hepatocellular carcinoma: A potential tumor metastasis biomarker.","date":"2019","source":"Cancer genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31109594","citation_count":4,"is_preprint":false},{"pmid":"37573517","id":"PMC_37573517","title":"SPART links autophagy machinery and lipid droplets in motor neurons.","date":"2023","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/37573517","citation_count":3,"is_preprint":false},{"pmid":"40985721","id":"PMC_40985721","title":"Hepatitis C virus NS3/4A protease cleaves SPG20, a key regulator of lipid droplet turnover, to promote lipid droplet formation.","date":"2025","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/40985721","citation_count":2,"is_preprint":false},{"pmid":"42161262","id":"PMC_42161262","title":"A CRISPR activation screen identifies SPART as a pan-orthoflavivirus restriction factor.","date":"2026","source":"Cell host & microbe","url":"https://pubmed.ncbi.nlm.nih.gov/42161262","citation_count":0,"is_preprint":false},{"pmid":"32661208","id":"PMC_32661208","title":"A novel missense mutation (c.1006C>T) of SPG20 gene associated with Troyer syndrome.","date":"2020","source":"Journal of genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32661208","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14483,"output_tokens":3658,"usd":0.04916,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11396,"output_tokens":4575,"usd":0.085678,"stage2_stop_reason":"end_turn"},"total_usd":0.134838,"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\": 2002,\n      \"finding\": \"SPG20 encodes spartin, which by comparative sequence analysis shares similarity with molecules involved in endosomal trafficking and with spastin (a microtubule-interacting HSP protein); a frameshift mutation in SPG20 causes Troyer syndrome.\",\n      \"method\": \"Genetic mapping, sequencing, and comparative sequence analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — sequence analysis and genetic mapping; functional inference from homology, not direct biochemical experiment, but replicated across subsequent studies\",\n      \"pmids\": [\"12134148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Spartin (SPG20) interacts with Eps15, a protein involved in endocytosis and cell proliferation; spartin is both cytosolic and membrane-associated.\",\n      \"method\": \"Yeast two-hybrid screen of adult human brain library, fusion protein pulldown, cellular redistribution assay, anti-spartin antibody fractionation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid confirmed by pulldown and redistribution assay, single lab, no reciprocal Co-IP\",\n      \"pmids\": [\"16036216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Spartin associates with lipid droplet surfaces and regulates lipid droplet size and number; it binds TIP47 and competes with adipophilin for LD occupancy; WWP1 (AIP5) binds spartin, transfers ubiquitin to it, removes it from LDs, and reduces its levels. The Troyer syndrome truncation mutant lacks these activities.\",\n      \"method\": \"Co-IP, RNA interference knockdown, overexpression, lipid droplet imaging, ubiquitination assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, RNAi, imaging, ubiquitination assay) in single lab, findings replicated in subsequent studies\",\n      \"pmids\": [\"19307600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Endogenous spartin localizes to a cytosolic pool that is recruited to endosomes and lipid droplets; cytosolic spartin is mono-ubiquitinated; spartin interacts via a PPXY motif with ubiquitin E3 ligases AIP4 (ITCH) and AIP5 (WWP1); the PPXY motif and these ligases are not required for spartin's own ubiquitination, suggesting spartin acts as an adaptor.\",\n      \"method\": \"Subcellular fractionation, immunofluorescence, endogenous protein immunoprecipitation, PPXY motif mutagenesis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous protein biochemistry, mutagenesis of PPXY motif, orthogonal to PMID 19307600 findings, consistent across two independent labs\",\n      \"pmids\": [\"19580544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The spartin MIT domain binds ESCRT-III protein IST1 with micromolar affinity (but not CHMP1-7); spartin co-localizes with IST1 at the midbody; IST1 depletion reduces spartin at midbodies; spartin depletion impairs cytokinesis; a structure-based F24D mutation in the MIT domain blocks the spartin–IST1 interaction, prevents midbody localization, and acts dominant-negatively to impair cytokinesis.\",\n      \"method\": \"Yeast two-hybrid, in vitro surface plasmon resonance, siRNA knockdown, immunofluorescence co-localization, dominant-negative mutation (F24D)\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — SPR binding kinetics, structure-based mutagenesis, siRNA phenotype, multiple orthogonal methods in one study\",\n      \"pmids\": [\"20719964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The plant-related senescence (PRS) domain of spartin interacts specifically with cardiolipin but not phosphatidylcholine or phosphatidylethanolamine; spartin knockdown depolarizes mitochondrial membrane potential and significantly decreases mitochondrial calcium uptake.\",\n      \"method\": \"Lipid-binding assay with purified PRS domain, siRNA knockdown in neuroblastoma cells, mitochondrial membrane potential measurements, mitochondrial calcium uptake assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct lipid-binding assay with domain construct plus functional siRNA readouts, single lab\",\n      \"pmids\": [\"21559443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SPG20 promoter hypermethylation silences spartin expression; spartin depletion in cancer cells causes cytokinesis arrest, reversed by inhibiting SPG20 methylation.\",\n      \"method\": \"Methylation-specific PCR, qRT-PCR, siRNA knockdown, cell cycle analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reversal of cytokinesis arrest by methylation inhibition provides mechanistic link, single lab\",\n      \"pmids\": [\"21499309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Spg20-/- mice show: (1) impaired cytokinesis in embryonic fibroblasts and binucleated chondrocytes in bone growth plates; (2) increased axon branching in cortical neurons reversed by reintroduction of spartin requiring its IST1 interaction; (3) elevated BMP/Smad1/5 phosphorylation in fibroblasts suggesting altered BMP receptor trafficking; (4) increased lipid droplet numbers and altered perilipin levels in adipose tissue.\",\n      \"method\": \"Spg20 knockout mice, primary neuronal culture, primary fibroblast culture, immunofluorescence, Western blot, rescue with wild-type spartin\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout model with multiple orthogonal cellular readouts and rescue experiments confirming mechanistic requirements\",\n      \"pmids\": [\"22619377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPART loss-of-function leads to decreased mitochondrial complex I (NADH dehydrogenase) activity, decreased ATP synthesis, defective mitochondrial membrane potential, increased ROS, and altered intracellular Ca2+ homeostasis; re-expression of wild-type spartin restores Ca2+ homeostasis.\",\n      \"method\": \"SH-SY5Y cell model with SPART frameshift mutation, enzymatic complex I activity assay, ATP synthesis assay, mitochondrial membrane potential measurement, ROS detection, Ca2+ imaging, wild-type rescue\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays with rescue, single lab, consistent with prior findings from PMID 21559443\",\n      \"pmids\": [\"31314595\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Knockout of SPG20/spartin activates the EGFR/MAPK signaling pathway to promote cell proliferation; EGFR kinase or ERK1/2 inhibitors rescue the proliferation phenotype caused by spartin loss.\",\n      \"method\": \"SPG20 knockout cells, in vitro proliferation assays, colony formation, Western blot for pathway activation, pharmacological inhibition with EGFR and ERK1/2 inhibitors, in vivo xenografts\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway placement by pharmacological rescue, single lab, two orthogonal approaches (inhibitors + knockout)\",\n      \"pmids\": [\"29673586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Mutant SPART causes impaired mitochondrial import of nuclear-encoded proteins, leading to significant decrease of CoQ10 biosynthesis enzymes COQ7 and COQ9 and severe reduction in CoQ content; CoQ supplementation restores cellular ATP levels to the same extent as re-expression of wild-type SPART.\",\n      \"method\": \"Patient-derived fibroblasts, mitochondrial protein import assay, mass spectrometry proteomics, CoQ content measurement, ATP assay, wild-type SPART rescue\",\n      \"journal\": \"Open biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mitochondrial import assay with two cell models and CoQ rescue, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"37433530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPG20 detects lipid-packing defects in damaged lysosomal membranes via sensory amphipathic helices before membrane rupture; SPG20 binds IST1 on damaged lysosomes and, when lipid-packing defects are extensive (e.g., during lipid peroxidation), recruits and activates ITCH to mark the lysosome with K63-linked ubiquitin chains, initiating lysophagy.\",\n      \"method\": \"Human cell-based assays, lysosomal damage assays (LLOMe), co-immunoprecipitation, ubiquitin linkage-specific antibodies, SPG20 amphipathic helix mutagenesis, IST1 binding assays, ITCH recruitment assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, mutagenesis of amphipathic helices, ubiquitin chain typing, functional lysophagy assay) in a single rigorous study\",\n      \"pmids\": [\"38503285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HCV NS3/4A protease cleaves SPG20 at Cys504 and Cys562; cleavage disrupts SPG20–TIP47 interaction and prevents ITCH recruitment to LD-associated ADRP/adipophilin, thereby blocking ubiquitin-dependent ADRP degradation and promoting large lipid droplet formation.\",\n      \"method\": \"Immunoblot of HCV-infected cells, NS3/4A transfection (active vs. inactive mutant), site-directed mutagenesis of cleavage sites, co-immunoprecipitation of SPG20 with TIP47, siRNA knockdown of ITCH, immunofluorescence\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — site-directed mutagenesis identifying specific cleavage sites, active-site inactive mutant controls, Co-IP, siRNA rescue, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"40985721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SPART interacts with and disrupts the endosomal localization of ITCH E3-ubiquitin ligase; ITCH ubiquitinates the ZIKV capsid to trigger viral uncoating; loss of SPART enhances ZIKV replication through an ITCH-dependent mechanism (effect absent in SPART-ITCH double knockouts), establishing SPART as a pan-orthoflavivirus restriction factor acting via ITCH-mediated capsid ubiquitination.\",\n      \"method\": \"Genome-wide CRISPR activation screen, SPART/ITCH single and double knockout cell lines, Spg20-/- and Itch-/- mice infected with ZIKV, viral replication assays, ITCH localization imaging, ubiquitination assays on viral capsid\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR screen validated by double-knockout epistasis in cells and in vivo mouse models, multiple orthogonal methods across cell and animal systems\",\n      \"pmids\": [\"42161262\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Spartin (SPART/SPG20) is a multifunctional scaffold protein with an N-terminal MIT domain that binds ESCRT-III protein IST1 to enable midbody localization and cytokinesis, a C-terminal plant-related senescence domain that binds cardiolipin and regulates mitochondrial membrane potential, Ca2+ homeostasis, and nuclear-encoded mitochondrial protein import (including CoQ biosynthesis enzymes); at lipid droplets, spartin binds TIP47 and recruits/activates the HECT E3 ubiquitin ligase ITCH to ubiquitinate and degrade the LD-coat protein ADRP/adipophilin, thereby driving LD turnover; on damaged lysosomes, spartin detects lipid-packing defects via sensory amphipathic helices, binds IST1, and activates ITCH to deposit K63-linked ubiquitin chains that initiate lysophagy; and in innate antiviral defense, spartin restricts orthoflavivirus replication by sequestering ITCH away from endosomes, thereby enabling ITCH-mediated ubiquitination of viral capsid and uncoating.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Spartin (SPART/SPG20) is a multifunctional adaptor protein that couples membrane and organelle quality control to the ubiquitin system, and its loss causes the autosomal recessive hereditary spastic paraplegia Troyer syndrome [#0]. Through its N-terminal MIT domain it binds the ESCRT-III protein IST1 with micromolar affinity, an interaction required for spartin's recruitment to the midbody and for completion of cytokinesis; a structure-based MIT mutation that abolishes IST1 binding blocks midbody localization and acts dominant-negatively [#4]. A central feature of spartin function is its role as a recruitment platform for HECT-family E3 ubiquitin ligases ITCH (AIP4) and WWP1 (AIP5), which it engages via a PPXY motif while itself acting as an adaptor rather than an obligate substrate [#3]. At lipid droplets, spartin binds TIP47, competes with adipophilin for droplet occupancy, and controls lipid droplet size and number through ITCH/WWP1-dependent ubiquitination [#2]. On damaged lysosomes, spartin senses lipid-packing defects through amphipathic helices, binds IST1, and recruits and activates ITCH to deposit K63-linked ubiquitin chains that initiate lysophagy [#11]. The same ITCH-targeting activity underlies antiviral restriction: spartin redistributes ITCH away from endosomes to enable ITCH-mediated ubiquitination of the orthoflavivirus capsid and viral uncoating, establishing spartin as a pan-orthoflavivirus restriction factor [#13]. Independently, its C-terminal plant-related senescence domain binds cardiolipin and supports mitochondrial membrane potential, calcium uptake, complex I activity, and nuclear-encoded mitochondrial protein import, including the CoQ biosynthetic enzymes COQ7 and COQ9 [#5, #8, #10]. In vivo, Spg20-deficient mice recapitulate impaired cytokinesis, increased neuronal axon branching reversed by IST1-binding-competent spartin, and lipid droplet accumulation [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established the gene-disease link and first functional context: a frameshift mutation in SPG20 causes Troyer syndrome, with sequence similarity to endosomal trafficking and spastin-like HSP proteins pointing toward membrane biology.\",\n      \"evidence\": \"Genetic mapping, sequencing, and comparative sequence analysis in Troyer syndrome families\",\n      \"pmids\": [\"12134148\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Function inferred from homology rather than biochemistry\", \"No direct demonstration of trafficking activity\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Provided the first direct interaction partner, linking spartin to endocytic machinery and showing it has both cytosolic and membrane-associated pools.\",\n      \"evidence\": \"Yeast two-hybrid of human brain library with pulldown and redistribution validation\",\n      \"pmids\": [\"16036216\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reciprocal Co-IP\", \"Functional consequence of Eps15 interaction not established\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined spartin as a lipid-droplet regulator and an adaptor for HECT E3 ligases, showing it binds TIP47, competes with adipophilin, and engages ITCH/WWP1 via a PPXY motif while acting as an adaptor rather than obligate substrate.\",\n      \"evidence\": \"Co-IP, RNAi, LD imaging, ubiquitination assays, and PPXY mutagenesis on endogenous protein across two labs\",\n      \"pmids\": [\"19307600\", \"19580544\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of ITCH/WWP1 substrates at LDs not yet defined\", \"How spartin selects between the two ligases unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved the mechanism of spartin's role in cell division: the MIT domain binds ESCRT-III IST1 to target spartin to the midbody and complete cytokinesis.\",\n      \"evidence\": \"SPR binding kinetics, structure-based F24D mutagenesis, siRNA, and co-localization imaging\",\n      \"pmids\": [\"20719964\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effector of midbody spartin not defined\", \"Relationship between MIT/IST1 axis and the LD/ligase functions unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified a distinct mitochondrial function: the PRS domain binds cardiolipin, and spartin loss depolarizes mitochondria and impairs calcium uptake, separating membrane lipid sensing from the MIT/ESCRT activity.\",\n      \"evidence\": \"Lipid-binding assay with purified PRS domain plus siRNA functional readouts in neuroblastoma\",\n      \"pmids\": [\"21559443\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanistic link between cardiolipin binding and membrane potential not delineated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed that epigenetic silencing of SPG20 by promoter hypermethylation phenocopies depletion, causing cytokinesis arrest reversible by demethylation, tying spartin loss to a cancer-relevant proliferation defect.\",\n      \"evidence\": \"Methylation-specific PCR, siRNA, and cell-cycle analysis with methylation-inhibition rescue\",\n      \"pmids\": [\"21499309\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish direct oncogenic mechanism\", \"Single lab\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Validated multiple spartin functions in vivo and established that the IST1 interaction is required to restrain neuronal axon branching, integrating cytokinesis, neuronal, BMP-signaling, and lipid-droplet phenotypes in a knockout animal.\",\n      \"evidence\": \"Spg20-/- mice with primary neuronal/fibroblast culture, imaging, Western blot, and spartin rescue\",\n      \"pmids\": [\"22619377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"BMP/Smad effect attributed to altered receptor trafficking but mechanism not resolved\", \"Adipose LD phenotype not linked to specific ligase activity\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Placed spartin loss upstream of EGFR/MAPK signaling, showing knockout activates this pathway to drive proliferation reversible by EGFR or ERK1/2 inhibition.\",\n      \"evidence\": \"SPG20 knockout cells, proliferation/colony assays, pathway Westerns, pharmacological rescue, and xenografts\",\n      \"pmids\": [\"29673586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between spartin and EGFR not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Deepened the mitochondrial phenotype, showing SPART loss reduces complex I activity and ATP synthesis, increases ROS, and disrupts Ca2+ homeostasis, with rescue restoring calcium handling.\",\n      \"evidence\": \"SH-SY5Y SPART frameshift model with complex I, ATP, membrane potential, ROS, Ca2+ assays and rescue\",\n      \"pmids\": [\"31314595\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether mitochondrial defects are primary or secondary to import failure not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided a mechanistic basis for the mitochondrial bioenergetic defect: mutant SPART impairs import of nuclear-encoded proteins including COQ7/COQ9, depleting CoQ, with CoQ supplementation restoring ATP comparably to wild-type rescue.\",\n      \"evidence\": \"Patient fibroblasts, mitochondrial import assay, MS proteomics, CoQ measurement, ATP assay, rescue\",\n      \"pmids\": [\"37433530\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How spartin supports the import machinery mechanistically unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Unified spartin's membrane-sensing and ligase-recruitment functions in lysophagy: amphipathic helices detect lipid-packing defects on damaged lysosomes, and spartin binds IST1 and activates ITCH to deposit K63 ubiquitin chains initiating lysosomal autophagy.\",\n      \"evidence\": \"Cell-based LLOMe damage assays, Co-IP, ubiquitin linkage typing, amphipathic helix mutagenesis, ITCH recruitment assays\",\n      \"pmids\": [\"38503285\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the ubiquitinated lysosomal substrate(s) not defined\", \"Threshold determining ITCH activation not quantified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated that a viral protease exploits the spartin-ITCH lipid-droplet pathway: HCV NS3/4A cleaves SPG20 at Cys504/Cys562, disrupting TIP47 binding and ITCH recruitment to block ADRP degradation and promote large LD formation.\",\n      \"evidence\": \"HCV infection/NS3-4A transfection, cleavage-site mutagenesis, Co-IP, ITCH siRNA, immunofluorescence\",\n      \"pmids\": [\"40985721\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether cleavage benefits viral replication directly not established here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Established spartin as a pan-orthoflavivirus restriction factor, showing it sequesters ITCH from endosomes to enable ITCH ubiquitination of viral capsid and uncoating, with epistasis confirming an ITCH-dependent mechanism.\",\n      \"evidence\": \"Genome-wide CRISPRa screen, SPART/ITCH single and double knockouts, Spg20-/- and Itch-/- mice, viral assays, capsid ubiquitination\",\n      \"pmids\": [\"42161262\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How spartin spatially redistributes ITCH at the molecular level not detailed\", \"Breadth across other virus families not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how spartin's distinct domain activities — MIT/IST1 targeting, PPXY-mediated E3 ligase recruitment, amphipathic membrane sensing, and PRS/cardiolipin-dependent mitochondrial support — are coordinated and which contributes to Troyer syndrome neuropathology.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model integrating the multiple domains\", \"Tissue-specific determinant of motor-neuron vulnerability unknown\", \"Direct ubiquitination substrates at each membrane site incompletely defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 11]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [5, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [4, 6, 7]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 2]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5, 8, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"IST1\", \"ITCH\", \"WWP1\", \"TIP47\", \"Eps15\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":{"gene":"SPART","tier":"GROUNDING","verdict":"Evidence-grounding concern","subtype":"fabrication","uniprot_band":"medium","rules_fired":"R7","issue":"R7: fabricated (no corpus paper): 37433530"},"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}