{"gene":"ATP8A1","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2006,"finding":"Purified murine Atp8a1 (ATPase II) is maximally activated by phosphatidylserine (PS) in a manner dependent on the sn-1,2-glycerol stereoisomer and multiple elements of the PS headgroup structure, is minimally activated by PE and phosphatidylglycerol, and is inactive in phosphatidylcholine, phosphatidic acid, or phosphatidylinositol micelles; its selectivity profile mirrors but is distinct from the plasma membrane PS flippase, and it is vanadate-sensitive, consistent with P-type ATPase mechanism.","method":"In vitro ATPase activity assay with purified Atp8a1 expressed in insect cells, tested against a panel of phospholipid structural variants","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro biochemical reconstitution with purified protein and systematic structural variant analysis in a single focused study","pmids":["16618126"],"is_preprint":false},{"year":2008,"finding":"Atp8a1 is expressed in red blood cell precursors and is present in mature RBC membranes; its flippase activity was established in purified yeast secretory vesicles where it translocates PS across the vesicle membrane in an ATP-dependent manner, and its ATPase activity is stimulated by PS and PE.","method":"In vitro PS translocation assay in purified Saccharomyces cerevisiae secretory vesicles expressing Atp8a1; ATPase activity assay; membrane fractionation","journal":"Journal of receptor, ligand and channel research","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — reconstitution in yeast vesicles establishes flippase activity, but single lab and limited orthogonal validation","pmids":["20224745"],"is_preprint":false},{"year":2011,"finding":"Atp8a1 is required for plasma membrane aminophospholipid translocase (APLT) activity in hippocampal neurons; Atp8a1 knockout mice show dramatic PS externalization in dentate gyrus, CA1, and CA3 cells without increased apoptosis; ectopic expression of wild-type Atp8a1 (but not a P-type phosphorylation-site mutant) increases the Vmax of PM-APLT activity in neuronal N18 cells, and expression of the phosphorylation-site mutant causes PS externalization.","method":"Atp8a1 knockout mouse model; annexin V-based PS externalization assay; ectopic expression and phosphorylation-site mutagenesis in N18 neuronal cells; APLT kinetic assays (Vmax, Km)","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — knockout model with direct PS externalization readout combined with mutagenesis and kinetic assays in neuronal cells, two orthogonal approaches","pmids":["22007859"],"is_preprint":false},{"year":2012,"finding":"ATP8A1 forms a phospholipid flippase complex with CDC50A; CDC50A associates with ATP8A1 and recruits it to the plasma membrane; depletion of ATP8A1 specifically inhibits inward translocation of PE (but not PS) at the plasma membrane of CHO cells, impairs membrane ruffle formation, and severely reduces cell migration.","method":"Co-immunoprecipitation; siRNA knockdown; phospholipid translocation assay (fluorescent lipid analogs); cell spreading, ruffle formation, and migration assays; PE-binding peptide and PE-synthesis-defective mutant cell lines","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional interaction established by Co-IP and knockdown, mechanistic link to PE translocation confirmed with orthogonal chemical and genetic tools","pmids":["23269685"],"is_preprint":false},{"year":2019,"finding":"ATP8A1 is highly expressed in murine and human platelets but is not present in the plasma membrane; during apoptosis, ATP8A1 is cleaved by the cysteine protease calpain, and this cleavage is indirectly prevented by caspase inhibition through blockage of calcium influx and subsequent calpain activation. In contrast, ATP8A1 remains intact in platelets activated with thrombin and collagen that also expose PS.","method":"Western blotting of platelet fractions; calpain inhibitor and caspase inhibitor treatment; calcium chelation; immunofluorescence/subcellular fractionation","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical identification of calpain cleavage with pharmacological dissection in two orthogonal activation conditions, single lab","pmids":["30674456"],"is_preprint":false},{"year":2021,"finding":"In alveolar type 2 (AT2) cells, AP-3 sorts ATP8A1 from early endosomes to lamellar bodies (lysosome-related organelles) through recognition of a C-terminal dileucine-based signal on ATP8A1; disruption of the AP-3/ATP8A1 interaction causes ATP8A1 accumulation in early/recycling endosomes, increases phosphatidylserine exposure on the cytosolic leaflet, and activates Yes-associated protein (YAP), augmenting cell migration and AT2 cell numbers.","method":"Mutagenesis of dileucine signal; co-immunoprecipitation; subcellular fractionation and live imaging; PS exposure assay; YAP activity reporter; siRNA knockdown; AP-3-deficient (HPS2) cell models","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (mutagenesis, Co-IP, localization, signaling readout) in a single focused study establishing AP-3-dependent sorting via a defined signal","pmids":["33990468"],"is_preprint":false},{"year":2023,"finding":"AP-3 targets the phospholipid flippase ATP8A1 to a subset of synaptic vesicles (SVs) in mouse hippocampal neurons; ATP8A1 on these SVs translocates PS to the cytoplasmic face, which recruits synapsin to that SV subset; loss of ATP8A1 recapitulates the high-frequency stimulation-specific SV mobilization defect seen with AP-3 loss, establishing that ATP8A1-mediated PS translocation and consequent synapsin recruitment enables high-frequency neurotransmitter release.","method":"AP-3 SV proteomics (mass spectrometry); ATP8A1 knockout mice; electrophysiology of hippocampal slices (high-frequency stimulation); synapsin recruitment assay; live imaging of SV dynamics","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — proteomics identification followed by genetic knockout with direct functional electrophysiological readout and mechanistic link to synapsin recruitment, rigorous controls","pmids":["37723322"],"is_preprint":false},{"year":2023,"finding":"Using coarse-grained molecular dynamics and binding free energy calculations on the ATP8A1-CDC50 complex, phospholipid binding to the transporter occurs early in the transport cycle when ATP8A1-CDC50 transitions from E2P to E2Pi-PL state, and electrostatic interactions of key transmembrane residues are critical drivers of the phospholipid transport free energy landscape.","method":"Coarse-grained molecular simulation; binding free energy calculations on cryo-EM-derived ATP8A1-CDC50 structure","journal":"Biomedicines","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational modeling only, no experimental validation of specific residues or states reported in this paper","pmids":["36831082"],"is_preprint":false},{"year":2023,"finding":"Atp8a1 knockout in mice causes loss of plasma membrane PS asymmetry in hematopoietic stem cells (HSCs), leading to decreased PTEN protein levels, activation of PI3K-AKT-mTORC1 signaling, increased JNK/AP-1 activity, and YAP1 phosphorylation changes, which collectively increase HSC proliferative activity and repopulation capacity.","method":"Atp8a1 knockout mouse; flow cytometry; competitive bone marrow transplantation; 5-FU stress assay; RNA sequencing; western blotting for PTEN, AKT, mTOR, JNK, YAP1; comet assay and immunofluorescence for DNA damage","journal":"Cellular oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockout model with multiple downstream pathway readouts by western blot and RNA-seq, single lab but orthogonal methods","pmids":["36930333"],"is_preprint":false},{"year":2024,"finding":"ATP8A1 co-localizes with BIG1 and BIG2 ARF-GEFs at the trans-Golgi Network (TGN); the cytosolic C-terminal tail of ATP8A1 binds the catalytic Sec7 domain of BIG1 and BIG2; expression of ATP8A1 (but not a C-terminal tail deletion mutant) increases generation of activated ARFs at the TGN and selectively increases recruitment of AP1, GGA2, and clathrin to TGN membranes, suggesting the ATP8A1 tail stimulates BIG1/BIG2 GEF catalytic activity to couple membrane deformation with vesicle coat assembly.","method":"Co-immunoprecipitation; co-localization by confocal microscopy; expression of wild-type vs. tail-deletion mutant ATP8A1; ARF activation assay; quantification of AP1/GGA2/clathrin recruitment by immunofluorescence","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, domain mutagenesis, and functional ARF/coat recruitment assays in one study, single lab","pmids":["38879142"],"is_preprint":false},{"year":2025,"finding":"ATP8A1 is enriched in Rab7-positive late endosomal compartments and preferentially flips PS from the luminal to the cytosolic leaflet of endosomal membranes (but not the inner leaflet of the plasma membrane); ATP8A1 depletion accelerates cargo transfer into intraluminal vesicles (ILVs) of multivesicular bodies (MVBs), alters EGFR signaling, and promotes ESCRT component recruitment by increasing luminal-leaflet PS loading on MVB limiting membranes.","method":"siRNA knockdown; PS biosensor (GFP-LactC2); subcellular fractionation; live imaging; cargo trafficking assays; EGFR signaling (western blot); ESCRT recruitment by immunofluorescence","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct PS topology assay combined with cargo trafficking and ESCRT recruitment readouts, single lab with multiple orthogonal approaches","pmids":["40083718"],"is_preprint":false},{"year":2021,"finding":"ATP8A1 is identified as the strongest binding partner of IFT27 by pulldown/interaction screening; however, global Atp8a1 knockout mice are fully fertile with normal sperm count, motility, and testis/epididymis histology, demonstrating ATP8A1 is dispensable for spermatogenesis despite this interaction.","method":"Co-immunoprecipitation/binding partner identification; Atp8a1 knockout mouse; sperm count and motility analysis; histology","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — binding confirmed and negative functional result rigorously established with knockout, single lab","pmids":["33821543"],"is_preprint":false}],"current_model":"ATP8A1 is a P4-type ATPase that forms a complex with the CDC50A chaperone subunit, which recruits it to specific membranes; it uses ATP hydrolysis (requiring phosphorylation of a conserved P-type site) to flip phosphatidylserine and phosphatidylethanolamine from the exoplasmic/luminal leaflet to the cytoplasmic leaflet of the plasma membrane, endosomes, lamellar bodies, and synaptic vesicles, with PS being the primary activating substrate; this lipid asymmetry activity regulates cell migration (via PE-dependent membrane ruffling), high-frequency synaptic vesicle release (via PS-dependent synapsin recruitment), hematopoietic stem cell proliferation (via PTEN/PI3K-AKT-mTORC1 signaling), TGN vesicle coat assembly (via BIG1/BIG2 GEF stimulation), and MVB/ESCRT sorting, while AP-3 directs its subcellular targeting through a C-terminal dileucine signal, and calpain cleaves and inactivates it during platelet apoptosis to permit sustained PS exposure."},"narrative":{"mechanistic_narrative":"ATP8A1 is a P4-type ATPase phospholipid flippase that uses vanadate-sensitive, phosphorylation-dependent ATP hydrolysis to translocate aminophospholipids from the exoplasmic/luminal leaflet to the cytoplasmic leaflet of cellular membranes, with phosphatidylserine (PS) serving as the principal activating substrate and phosphatidylethanolamine (PE) as a secondary one [PMID:16618126, PMID:20224745, PMID:22007859]. It functions as a heteromeric complex with the CDC50A chaperone, which associates with ATP8A1 and recruits it to the plasma membrane [PMID:23269685]. Catalysis requires an intact P-type phosphorylation site, as mutation of this residue abolishes translocase activity and instead causes PS externalization [PMID:22007859]. Through this lipid-flipping activity ATP8A1 controls diverse membrane-dependent processes: it maintains plasma membrane aminophospholipid asymmetry in hippocampal neurons [PMID:22007859], drives PE-dependent membrane ruffling and cell migration [PMID:23269685], and on a synaptic-vesicle subset translocates PS to the cytoplasmic face to recruit synapsin and sustain high-frequency neurotransmitter release [PMID:37723322]. Its subcellular targeting is governed by the AP-3 adaptor, which recognizes a C-terminal dileucine signal to sort ATP8A1 from endosomes to lamellar bodies and synaptic vesicles [PMID:33990468, PMID:37723322]. ATP8A1 also acts at the trans-Golgi network, where its cytosolic C-terminal tail binds and stimulates the Sec7 domain of the ARF-GEFs BIG1 and BIG2 to promote ARF activation and AP1/GGA2/clathrin coat recruitment [PMID:38879142], and at Rab7-positive late endosomes, where it regulates PS topology on multivesicular body limiting membranes to control ESCRT recruitment, intraluminal vesicle cargo sorting, and EGFR signaling [PMID:40083718]. Loss of ATP8A1 lipid asymmetry activity feeds into downstream signaling, modulating PTEN/PI3K-AKT-mTORC1 and YAP1 outputs that govern hematopoietic stem cell proliferation and AT2 cell behavior [PMID:33990468, PMID:36930333]. During platelet apoptosis, the cysteine protease calpain cleaves and inactivates ATP8A1, permitting sustained PS exposure [PMID:30674456].","teleology":[{"year":2006,"claim":"Established that ATP8A1 is a P-type ATPase whose activity is specifically driven by phosphatidylserine, defining its substrate preference at the biochemical level.","evidence":"In vitro ATPase assay with purified Atp8a1 from insect cells against a panel of phospholipid structural variants","pmids":["16618126"],"confidence":"High","gaps":["ATPase stimulation alone does not demonstrate vectorial lipid transport","no in vivo membrane context","CDC50A requirement not yet known"]},{"year":2008,"claim":"Demonstrated that ATP8A1 is a bona fide ATP-dependent flippase that vectorially translocates PS across a membrane, moving beyond ATPase stimulation to actual transport.","evidence":"PS translocation assay in purified yeast secretory vesicles expressing Atp8a1; ATPase assay; RBC membrane fractionation","pmids":["20224745"],"confidence":"Medium","gaps":["heterologous yeast system may not reflect native partner requirements","single lab","physiological membrane localization unresolved"]},{"year":2011,"claim":"Linked ATP8A1 catalytic mechanism to a physiological function by showing its phosphorylation site is required for plasma membrane aminophospholipid translocase activity and PS asymmetry in neurons.","evidence":"Atp8a1 knockout mice with annexin V PS-externalization readout; phosphorylation-site mutagenesis and APLT kinetics in N18 neuronal cells","pmids":["22007859"],"confidence":"High","gaps":["PS externalization in knockout did not increase apoptosis, leaving downstream consequences unclear","chaperone subunit not addressed","did not distinguish direct vs indirect contribution to APLT"]},{"year":2012,"claim":"Identified CDC50A as the obligate partner that recruits ATP8A1 to the plasma membrane and resolved a distinct PE-translocation role driving membrane ruffling and migration.","evidence":"Co-IP, siRNA knockdown, fluorescent-lipid translocation assays, and ruffle/migration assays in CHO cells with PE-binding peptide and PE-synthesis mutants","pmids":["23269685"],"confidence":"High","gaps":["PE versus PS substrate split across studies/systems not fully reconciled","stoichiometry of the ATP8A1-CDC50A complex not defined here","in vivo migration relevance untested"]},{"year":2019,"claim":"Showed how ATP8A1 activity is terminated during apoptosis, identifying calpain cleavage as the switch permitting sustained platelet PS exposure.","evidence":"Western blotting of platelet fractions with calpain/caspase inhibitors and calcium chelation across apoptotic versus thrombin/collagen activation","pmids":["30674456"],"confidence":"Medium","gaps":["cleavage site not mapped","single lab","direct demonstration that cleavage abolishes flippase activity not shown"]},{"year":2021,"claim":"Defined the trafficking logic of ATP8A1, showing AP-3 recognizes a C-terminal dileucine signal to deliver it to lamellar bodies and linking mislocalization to PS topology and YAP-driven migration.","evidence":"Dileucine mutagenesis, Co-IP, fractionation, PS-exposure and YAP reporter assays in AP-3-deficient (HPS2) AT2 cell models","pmids":["33990468"],"confidence":"High","gaps":["mechanism coupling cytosolic PS to YAP activation not resolved","single tissue context","did not test other adaptor contributions"]},{"year":2021,"claim":"Tested whether the ATP8A1-IFT27 interaction confers a reproductive function, establishing ATP8A1 is dispensable for spermatogenesis despite being IFT27's strongest binding partner.","evidence":"Pulldown interaction screening plus Atp8a1 knockout mouse fertility, sperm, and histology analysis","pmids":["33821543"],"confidence":"Medium","gaps":["functional meaning of the IFT27 interaction unexplained","possible redundancy with paralogs not excluded","no ciliary phenotype assessment beyond reproduction"]},{"year":2023,"claim":"Connected AP-3 targeting to a defined neuronal function, showing ATP8A1 flips PS on a synaptic-vesicle subset to recruit synapsin and enable high-frequency release.","evidence":"AP-3 SV proteomics, Atp8a1 knockout mice, hippocampal slice electrophysiology, and synapsin recruitment/live SV imaging","pmids":["37723322"],"confidence":"High","gaps":["how synapsin reads cytoplasmic-leaflet PS mechanistically not detailed","fraction of SVs carrying ATP8A1 not quantified structurally","interplay with other SV flippases unknown"]},{"year":2023,"claim":"Extended ATP8A1's role to hematopoietic stem cells, linking loss of PS asymmetry to PTEN/PI3K-AKT-mTORC1 and YAP1 signaling that boosts HSC proliferation and repopulation.","evidence":"Atp8a1 knockout mouse with flow cytometry, competitive transplantation, RNA-seq, and pathway western blots","pmids":["36930333"],"confidence":"Medium","gaps":["direct mechanistic link between membrane PS and PTEN regulation not established","single lab","causality versus correlation among pathway changes unresolved"]},{"year":2023,"claim":"Provided a computational model of the transport cycle, placing phospholipid binding at the E2P to E2Pi-PL transition and highlighting transmembrane electrostatics.","evidence":"Coarse-grained molecular dynamics and binding free energy calculations on the cryo-EM ATP8A1-CDC50 structure","pmids":["36831082"],"confidence":"Low","gaps":["computational only, no experimental validation of predicted residues or states","predicted key residues not mutationally tested","model assumes the cryo-EM conformations sampled"]},{"year":2024,"claim":"Revealed a moonlighting role at the TGN in which the ATP8A1 cytosolic tail stimulates BIG1/BIG2 GEF activity to couple lipid flipping to ARF activation and vesicle coat assembly.","evidence":"Reciprocal Co-IP, confocal co-localization, tail-deletion mutagenesis, ARF activation assays, and AP1/GGA2/clathrin recruitment quantification","pmids":["38879142"],"confidence":"Medium","gaps":["whether GEF stimulation requires catalytic flippase activity untested","single lab","in vivo TGN trafficking consequence not shown"]},{"year":2025,"claim":"Established a late-endosomal function, showing ATP8A1 controls MVB-limiting-membrane PS topology to regulate ESCRT recruitment, ILV cargo sorting, and EGFR signaling.","evidence":"siRNA knockdown, GFP-LactC2 PS biosensor, fractionation, cargo trafficking and ESCRT recruitment assays, EGFR western blot","pmids":["40083718"],"confidence":"Medium","gaps":["mechanism by which luminal-leaflet PS recruits ESCRT not defined","single lab","relationship to AP-3-dependent endosomal sorting not integrated"]},{"year":null,"claim":"How a single flippase coordinates its distinct PS- versus PE-flipping activities across plasma membrane, TGN, endosomes, and synaptic vesicles, and how cytosolic-leaflet aminophospholipid changes are transduced into PTEN/YAP/synapsin/ESCRT outputs, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["unified structural basis for substrate switching not established","direct molecular sensors of cytosolic PS/PE in each pathway unidentified","tissue-specific phenotypic hierarchy of ATP8A1 loss not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[1,3,6,10]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,3]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[5,10]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[9]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[6]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[5,9,10]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,10]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[5,6]}],"complexes":["ATP8A1-CDC50A flippase complex"],"partners":["CDC50A","BIG1","BIG2","IFT27"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y2Q0","full_name":"Phospholipid-transporting ATPase IA","aliases":["ATPase class I type 8A member 1","Chromaffin granule ATPase II","P4-ATPase flippase complex alpha subunit ATP8A1"],"length_aa":1164,"mass_kda":131.4,"function":"Catalytic component of a P4-ATPase flippase complex which catalyzes the hydrolysis of ATP coupled to the transport of aminophospholipids from the outer to the inner leaflet of various membranes and ensures the maintenance of asymmetric distribution of phospholipids (PubMed:31416931). Phospholipid translocation also seems to be implicated in vesicle formation and in uptake of lipid signaling molecules. In vitro, its ATPase activity is selectively and stereospecifically stimulated by phosphatidylserine (PS) (PubMed:31416931). The flippase complex ATP8A1:TMEM30A seems to play a role in regulation of cell migration probably involving flippase-mediated translocation of phosphatidylethanolamine (PE) at the cell membrane (By similarity). Acts as aminophospholipid translocase at the cell membrane in neuronal cells (By similarity)","subcellular_location":"Cytoplasmic vesicle, secretory vesicle, chromaffin granule membrane; Cytoplasmic granule; Cell membrane; Endoplasmic reticulum; Golgi apparatus","url":"https://www.uniprot.org/uniprotkb/Q9Y2Q0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATP8A1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ATP8A1","total_profiled":1310},"omim":[{"mim_id":"615268","title":"CEREBELLAR ATAXIA, IMPAIRED INTELLECTUAL DEVELOPMENT, AND DYSEQUILIBRIUM SYNDROME 4; CAMRQ4","url":"https://www.omim.org/entry/615268"},{"mim_id":"613285","title":"DEAFNESS, AUTOSOMAL RECESSIVE 25; DFNB25","url":"https://www.omim.org/entry/613285"},{"mim_id":"609542","title":"ATPase, CLASS I, TYPE 8A, MEMBER 1; ATP8A1","url":"https://www.omim.org/entry/609542"},{"mim_id":"607680","title":"ZINC FINGER PROTEIN 363; ZNF363","url":"https://www.omim.org/entry/607680"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"thyroid gland","ntpm":37.1}],"url":"https://www.proteinatlas.org/search/ATP8A1"},"hgnc":{"alias_symbol":["ATPIA"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y2Q0","domains":[{"cath_id":"-","chopping":"54-134","consensus_level":"medium","plddt":83.2372,"start":54,"end":134},{"cath_id":"2.70.150.10","chopping":"152-280","consensus_level":"high","plddt":84.6159,"start":152,"end":280},{"cath_id":"3.40.50.1000","chopping":"372-416_666-845","consensus_level":"medium","plddt":87.6192,"start":372,"end":845},{"cath_id":"3.40.1110.10","chopping":"420-434_457-663_1140-1154","consensus_level":"high","plddt":86.2361,"start":420,"end":1154},{"cath_id":"-","chopping":"854-1095","consensus_level":"medium","plddt":88.6848,"start":854,"end":1095},{"cath_id":"1.10.287","chopping":"290-356","consensus_level":"medium","plddt":84.2963,"start":290,"end":356}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y2Q0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y2Q0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y2Q0-F1-predicted_aligned_error_v6.png","plddt_mean":82.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATP8A1","jax_strain_url":"https://www.jax.org/strain/search?query=ATP8A1"},"sequence":{"accession":"Q9Y2Q0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y2Q0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y2Q0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y2Q0"}},"corpus_meta":[{"pmid":"23269685","id":"PMC_23269685","title":"Role for phospholipid flippase complex of ATP8A1 and CDC50A proteins in cell migration.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23269685","citation_count":76,"is_preprint":false},{"pmid":"26415732","id":"PMC_26415732","title":"MiR-140-3p suppressed cell growth and invasion by downregulating the expression of ATP8A1 in non-small cell lung cancer.","date":"2015","source":"Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26415732","citation_count":64,"is_preprint":false},{"pmid":"16618126","id":"PMC_16618126","title":"Lipid specific activation of the murine P4-ATPase Atp8a1 (ATPase II).","date":"2006","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16618126","citation_count":64,"is_preprint":false},{"pmid":"22007859","id":"PMC_22007859","title":"Atp8a1 deficiency is associated with phosphatidylserine externalization in hippocampus and delayed hippocampus-dependent learning.","date":"2011","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22007859","citation_count":60,"is_preprint":false},{"pmid":"33990468","id":"PMC_33990468","title":"AP-3-dependent targeting of flippase ATP8A1 to lamellar bodies suppresses activation of YAP in alveolar epithelial type 2 cells.","date":"2021","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/33990468","citation_count":32,"is_preprint":false},{"pmid":"20224745","id":"PMC_20224745","title":"ATP8A1 activity and phosphatidylserine transbilayer movement.","date":"2008","source":"Journal of receptor, ligand and channel research","url":"https://pubmed.ncbi.nlm.nih.gov/20224745","citation_count":23,"is_preprint":false},{"pmid":"27287255","id":"PMC_27287255","title":"Aberrant hippocampal Atp8a1 levels are associated with altered synaptic strength, electrical activity, and 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pathology","url":"https://pubmed.ncbi.nlm.nih.gov/31966623","citation_count":9,"is_preprint":false},{"pmid":"36930333","id":"PMC_36930333","title":"Atp8a1 deletion increases the proliferative activity of hematopoietic stem cells by impairing PTEN function.","date":"2023","source":"Cellular oncology (Dordrecht, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/36930333","citation_count":6,"is_preprint":false},{"pmid":"33821543","id":"PMC_33821543","title":"ATP8a1, an IFT27 binding partner, is dispensable for spermatogenesis and male fertility.","date":"2021","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/33821543","citation_count":4,"is_preprint":false},{"pmid":"36831082","id":"PMC_36831082","title":"Exploring the Phospholipid Transport Mechanism of ATP8A1-CDC50.","date":"2023","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/36831082","citation_count":4,"is_preprint":false},{"pmid":"38879142","id":"PMC_38879142","title":"The lipid flippase ATP8A1 regulates the recruitment of ARF effectors to the trans-Golgi Network.","date":"2024","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/38879142","citation_count":3,"is_preprint":false},{"pmid":"40679788","id":"PMC_40679788","title":"circRNA_Atp8a1 Promotes Glycolytic Reprogramming in Damage of Intestinal Mucosal Barrier by Upregulating IGF2 through miR-200b-3p.","date":"2025","source":"Tissue engineering and regenerative medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40679788","citation_count":2,"is_preprint":false},{"pmid":"40083718","id":"PMC_40083718","title":"ATP8A1-translocated endosomal phosphatidylserine fine-tunes the multivesicular body formation and the endo-lysosomal traffic.","date":"2025","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/40083718","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.11.13.623339","title":"Lipid flippases ATP9A and ATP9B form a complex and contribute to the secretory pathway from the Golgi apparatus","date":"2024-11-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.13.623339","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.09.15.613099","title":"TAT-1, a phosphatidylserine flippase, affects molting and regulates membrane trafficking in the epidermis of  <i>C. elegans</i>","date":"2024-09-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.15.613099","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.02.616385","title":"Tissue-specific transcriptomics uncovers novel craniofacial genes underlying jaw divergence in specialist pupfishes","date":"2024-10-03","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.02.616385","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12184,"output_tokens":3644,"usd":0.045606,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11317,"output_tokens":4624,"usd":0.086093,"stage2_stop_reason":"end_turn"},"total_usd":0.131699,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"Purified murine Atp8a1 (ATPase II) is maximally activated by phosphatidylserine (PS) in a manner dependent on the sn-1,2-glycerol stereoisomer and multiple elements of the PS headgroup structure, is minimally activated by PE and phosphatidylglycerol, and is inactive in phosphatidylcholine, phosphatidic acid, or phosphatidylinositol micelles; its selectivity profile mirrors but is distinct from the plasma membrane PS flippase, and it is vanadate-sensitive, consistent with P-type ATPase mechanism.\",\n      \"method\": \"In vitro ATPase activity assay with purified Atp8a1 expressed in insect cells, tested against a panel of phospholipid structural variants\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro biochemical reconstitution with purified protein and systematic structural variant analysis in a single focused study\",\n      \"pmids\": [\"16618126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Atp8a1 is expressed in red blood cell precursors and is present in mature RBC membranes; its flippase activity was established in purified yeast secretory vesicles where it translocates PS across the vesicle membrane in an ATP-dependent manner, and its ATPase activity is stimulated by PS and PE.\",\n      \"method\": \"In vitro PS translocation assay in purified Saccharomyces cerevisiae secretory vesicles expressing Atp8a1; ATPase activity assay; membrane fractionation\",\n      \"journal\": \"Journal of receptor, ligand and channel research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — reconstitution in yeast vesicles establishes flippase activity, but single lab and limited orthogonal validation\",\n      \"pmids\": [\"20224745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Atp8a1 is required for plasma membrane aminophospholipid translocase (APLT) activity in hippocampal neurons; Atp8a1 knockout mice show dramatic PS externalization in dentate gyrus, CA1, and CA3 cells without increased apoptosis; ectopic expression of wild-type Atp8a1 (but not a P-type phosphorylation-site mutant) increases the Vmax of PM-APLT activity in neuronal N18 cells, and expression of the phosphorylation-site mutant causes PS externalization.\",\n      \"method\": \"Atp8a1 knockout mouse model; annexin V-based PS externalization assay; ectopic expression and phosphorylation-site mutagenesis in N18 neuronal cells; APLT kinetic assays (Vmax, Km)\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — knockout model with direct PS externalization readout combined with mutagenesis and kinetic assays in neuronal cells, two orthogonal approaches\",\n      \"pmids\": [\"22007859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ATP8A1 forms a phospholipid flippase complex with CDC50A; CDC50A associates with ATP8A1 and recruits it to the plasma membrane; depletion of ATP8A1 specifically inhibits inward translocation of PE (but not PS) at the plasma membrane of CHO cells, impairs membrane ruffle formation, and severely reduces cell migration.\",\n      \"method\": \"Co-immunoprecipitation; siRNA knockdown; phospholipid translocation assay (fluorescent lipid analogs); cell spreading, ruffle formation, and migration assays; PE-binding peptide and PE-synthesis-defective mutant cell lines\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional interaction established by Co-IP and knockdown, mechanistic link to PE translocation confirmed with orthogonal chemical and genetic tools\",\n      \"pmids\": [\"23269685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ATP8A1 is highly expressed in murine and human platelets but is not present in the plasma membrane; during apoptosis, ATP8A1 is cleaved by the cysteine protease calpain, and this cleavage is indirectly prevented by caspase inhibition through blockage of calcium influx and subsequent calpain activation. In contrast, ATP8A1 remains intact in platelets activated with thrombin and collagen that also expose PS.\",\n      \"method\": \"Western blotting of platelet fractions; calpain inhibitor and caspase inhibitor treatment; calcium chelation; immunofluorescence/subcellular fractionation\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical identification of calpain cleavage with pharmacological dissection in two orthogonal activation conditions, single lab\",\n      \"pmids\": [\"30674456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In alveolar type 2 (AT2) cells, AP-3 sorts ATP8A1 from early endosomes to lamellar bodies (lysosome-related organelles) through recognition of a C-terminal dileucine-based signal on ATP8A1; disruption of the AP-3/ATP8A1 interaction causes ATP8A1 accumulation in early/recycling endosomes, increases phosphatidylserine exposure on the cytosolic leaflet, and activates Yes-associated protein (YAP), augmenting cell migration and AT2 cell numbers.\",\n      \"method\": \"Mutagenesis of dileucine signal; co-immunoprecipitation; subcellular fractionation and live imaging; PS exposure assay; YAP activity reporter; siRNA knockdown; AP-3-deficient (HPS2) cell models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (mutagenesis, Co-IP, localization, signaling readout) in a single focused study establishing AP-3-dependent sorting via a defined signal\",\n      \"pmids\": [\"33990468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"AP-3 targets the phospholipid flippase ATP8A1 to a subset of synaptic vesicles (SVs) in mouse hippocampal neurons; ATP8A1 on these SVs translocates PS to the cytoplasmic face, which recruits synapsin to that SV subset; loss of ATP8A1 recapitulates the high-frequency stimulation-specific SV mobilization defect seen with AP-3 loss, establishing that ATP8A1-mediated PS translocation and consequent synapsin recruitment enables high-frequency neurotransmitter release.\",\n      \"method\": \"AP-3 SV proteomics (mass spectrometry); ATP8A1 knockout mice; electrophysiology of hippocampal slices (high-frequency stimulation); synapsin recruitment assay; live imaging of SV dynamics\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — proteomics identification followed by genetic knockout with direct functional electrophysiological readout and mechanistic link to synapsin recruitment, rigorous controls\",\n      \"pmids\": [\"37723322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Using coarse-grained molecular dynamics and binding free energy calculations on the ATP8A1-CDC50 complex, phospholipid binding to the transporter occurs early in the transport cycle when ATP8A1-CDC50 transitions from E2P to E2Pi-PL state, and electrostatic interactions of key transmembrane residues are critical drivers of the phospholipid transport free energy landscape.\",\n      \"method\": \"Coarse-grained molecular simulation; binding free energy calculations on cryo-EM-derived ATP8A1-CDC50 structure\",\n      \"journal\": \"Biomedicines\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational modeling only, no experimental validation of specific residues or states reported in this paper\",\n      \"pmids\": [\"36831082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Atp8a1 knockout in mice causes loss of plasma membrane PS asymmetry in hematopoietic stem cells (HSCs), leading to decreased PTEN protein levels, activation of PI3K-AKT-mTORC1 signaling, increased JNK/AP-1 activity, and YAP1 phosphorylation changes, which collectively increase HSC proliferative activity and repopulation capacity.\",\n      \"method\": \"Atp8a1 knockout mouse; flow cytometry; competitive bone marrow transplantation; 5-FU stress assay; RNA sequencing; western blotting for PTEN, AKT, mTOR, JNK, YAP1; comet assay and immunofluorescence for DNA damage\",\n      \"journal\": \"Cellular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockout model with multiple downstream pathway readouts by western blot and RNA-seq, single lab but orthogonal methods\",\n      \"pmids\": [\"36930333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ATP8A1 co-localizes with BIG1 and BIG2 ARF-GEFs at the trans-Golgi Network (TGN); the cytosolic C-terminal tail of ATP8A1 binds the catalytic Sec7 domain of BIG1 and BIG2; expression of ATP8A1 (but not a C-terminal tail deletion mutant) increases generation of activated ARFs at the TGN and selectively increases recruitment of AP1, GGA2, and clathrin to TGN membranes, suggesting the ATP8A1 tail stimulates BIG1/BIG2 GEF catalytic activity to couple membrane deformation with vesicle coat assembly.\",\n      \"method\": \"Co-immunoprecipitation; co-localization by confocal microscopy; expression of wild-type vs. tail-deletion mutant ATP8A1; ARF activation assay; quantification of AP1/GGA2/clathrin recruitment by immunofluorescence\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, domain mutagenesis, and functional ARF/coat recruitment assays in one study, single lab\",\n      \"pmids\": [\"38879142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ATP8A1 is enriched in Rab7-positive late endosomal compartments and preferentially flips PS from the luminal to the cytosolic leaflet of endosomal membranes (but not the inner leaflet of the plasma membrane); ATP8A1 depletion accelerates cargo transfer into intraluminal vesicles (ILVs) of multivesicular bodies (MVBs), alters EGFR signaling, and promotes ESCRT component recruitment by increasing luminal-leaflet PS loading on MVB limiting membranes.\",\n      \"method\": \"siRNA knockdown; PS biosensor (GFP-LactC2); subcellular fractionation; live imaging; cargo trafficking assays; EGFR signaling (western blot); ESCRT recruitment by immunofluorescence\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct PS topology assay combined with cargo trafficking and ESCRT recruitment readouts, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"40083718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ATP8A1 is identified as the strongest binding partner of IFT27 by pulldown/interaction screening; however, global Atp8a1 knockout mice are fully fertile with normal sperm count, motility, and testis/epididymis histology, demonstrating ATP8A1 is dispensable for spermatogenesis despite this interaction.\",\n      \"method\": \"Co-immunoprecipitation/binding partner identification; Atp8a1 knockout mouse; sperm count and motility analysis; histology\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — binding confirmed and negative functional result rigorously established with knockout, single lab\",\n      \"pmids\": [\"33821543\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATP8A1 is a P4-type ATPase that forms a complex with the CDC50A chaperone subunit, which recruits it to specific membranes; it uses ATP hydrolysis (requiring phosphorylation of a conserved P-type site) to flip phosphatidylserine and phosphatidylethanolamine from the exoplasmic/luminal leaflet to the cytoplasmic leaflet of the plasma membrane, endosomes, lamellar bodies, and synaptic vesicles, with PS being the primary activating substrate; this lipid asymmetry activity regulates cell migration (via PE-dependent membrane ruffling), high-frequency synaptic vesicle release (via PS-dependent synapsin recruitment), hematopoietic stem cell proliferation (via PTEN/PI3K-AKT-mTORC1 signaling), TGN vesicle coat assembly (via BIG1/BIG2 GEF stimulation), and MVB/ESCRT sorting, while AP-3 directs its subcellular targeting through a C-terminal dileucine signal, and calpain cleaves and inactivates it during platelet apoptosis to permit sustained PS exposure.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATP8A1 is a P4-type ATPase phospholipid flippase that uses vanadate-sensitive, phosphorylation-dependent ATP hydrolysis to translocate aminophospholipids from the exoplasmic/luminal leaflet to the cytoplasmic leaflet of cellular membranes, with phosphatidylserine (PS) serving as the principal activating substrate and phosphatidylethanolamine (PE) as a secondary one [#0, #1, #2]. It functions as a heteromeric complex with the CDC50A chaperone, which associates with ATP8A1 and recruits it to the plasma membrane [#3]. Catalysis requires an intact P-type phosphorylation site, as mutation of this residue abolishes translocase activity and instead causes PS externalization [#2]. Through this lipid-flipping activity ATP8A1 controls diverse membrane-dependent processes: it maintains plasma membrane aminophospholipid asymmetry in hippocampal neurons [#2], drives PE-dependent membrane ruffling and cell migration [#3], and on a synaptic-vesicle subset translocates PS to the cytoplasmic face to recruit synapsin and sustain high-frequency neurotransmitter release [#6]. Its subcellular targeting is governed by the AP-3 adaptor, which recognizes a C-terminal dileucine signal to sort ATP8A1 from endosomes to lamellar bodies and synaptic vesicles [#5, #6]. ATP8A1 also acts at the trans-Golgi network, where its cytosolic C-terminal tail binds and stimulates the Sec7 domain of the ARF-GEFs BIG1 and BIG2 to promote ARF activation and AP1/GGA2/clathrin coat recruitment [#9], and at Rab7-positive late endosomes, where it regulates PS topology on multivesicular body limiting membranes to control ESCRT recruitment, intraluminal vesicle cargo sorting, and EGFR signaling [#10]. Loss of ATP8A1 lipid asymmetry activity feeds into downstream signaling, modulating PTEN/PI3K-AKT-mTORC1 and YAP1 outputs that govern hematopoietic stem cell proliferation and AT2 cell behavior [#5, #8]. During platelet apoptosis, the cysteine protease calpain cleaves and inactivates ATP8A1, permitting sustained PS exposure [#4].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that ATP8A1 is a P-type ATPase whose activity is specifically driven by phosphatidylserine, defining its substrate preference at the biochemical level.\",\n      \"evidence\": \"In vitro ATPase assay with purified Atp8a1 from insect cells against a panel of phospholipid structural variants\",\n      \"pmids\": [\"16618126\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ATPase stimulation alone does not demonstrate vectorial lipid transport\", \"no in vivo membrane context\", \"CDC50A requirement not yet known\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated that ATP8A1 is a bona fide ATP-dependent flippase that vectorially translocates PS across a membrane, moving beyond ATPase stimulation to actual transport.\",\n      \"evidence\": \"PS translocation assay in purified yeast secretory vesicles expressing Atp8a1; ATPase assay; RBC membrane fractionation\",\n      \"pmids\": [\"20224745\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"heterologous yeast system may not reflect native partner requirements\", \"single lab\", \"physiological membrane localization unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linked ATP8A1 catalytic mechanism to a physiological function by showing its phosphorylation site is required for plasma membrane aminophospholipid translocase activity and PS asymmetry in neurons.\",\n      \"evidence\": \"Atp8a1 knockout mice with annexin V PS-externalization readout; phosphorylation-site mutagenesis and APLT kinetics in N18 neuronal cells\",\n      \"pmids\": [\"22007859\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PS externalization in knockout did not increase apoptosis, leaving downstream consequences unclear\", \"chaperone subunit not addressed\", \"did not distinguish direct vs indirect contribution to APLT\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified CDC50A as the obligate partner that recruits ATP8A1 to the plasma membrane and resolved a distinct PE-translocation role driving membrane ruffling and migration.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, fluorescent-lipid translocation assays, and ruffle/migration assays in CHO cells with PE-binding peptide and PE-synthesis mutants\",\n      \"pmids\": [\"23269685\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PE versus PS substrate split across studies/systems not fully reconciled\", \"stoichiometry of the ATP8A1-CDC50A complex not defined here\", \"in vivo migration relevance untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed how ATP8A1 activity is terminated during apoptosis, identifying calpain cleavage as the switch permitting sustained platelet PS exposure.\",\n      \"evidence\": \"Western blotting of platelet fractions with calpain/caspase inhibitors and calcium chelation across apoptotic versus thrombin/collagen activation\",\n      \"pmids\": [\"30674456\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"cleavage site not mapped\", \"single lab\", \"direct demonstration that cleavage abolishes flippase activity not shown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the trafficking logic of ATP8A1, showing AP-3 recognizes a C-terminal dileucine signal to deliver it to lamellar bodies and linking mislocalization to PS topology and YAP-driven migration.\",\n      \"evidence\": \"Dileucine mutagenesis, Co-IP, fractionation, PS-exposure and YAP reporter assays in AP-3-deficient (HPS2) AT2 cell models\",\n      \"pmids\": [\"33990468\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"mechanism coupling cytosolic PS to YAP activation not resolved\", \"single tissue context\", \"did not test other adaptor contributions\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Tested whether the ATP8A1-IFT27 interaction confers a reproductive function, establishing ATP8A1 is dispensable for spermatogenesis despite being IFT27's strongest binding partner.\",\n      \"evidence\": \"Pulldown interaction screening plus Atp8a1 knockout mouse fertility, sperm, and histology analysis\",\n      \"pmids\": [\"33821543\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"functional meaning of the IFT27 interaction unexplained\", \"possible redundancy with paralogs not excluded\", \"no ciliary phenotype assessment beyond reproduction\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected AP-3 targeting to a defined neuronal function, showing ATP8A1 flips PS on a synaptic-vesicle subset to recruit synapsin and enable high-frequency release.\",\n      \"evidence\": \"AP-3 SV proteomics, Atp8a1 knockout mice, hippocampal slice electrophysiology, and synapsin recruitment/live SV imaging\",\n      \"pmids\": [\"37723322\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"how synapsin reads cytoplasmic-leaflet PS mechanistically not detailed\", \"fraction of SVs carrying ATP8A1 not quantified structurally\", \"interplay with other SV flippases unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended ATP8A1's role to hematopoietic stem cells, linking loss of PS asymmetry to PTEN/PI3K-AKT-mTORC1 and YAP1 signaling that boosts HSC proliferation and repopulation.\",\n      \"evidence\": \"Atp8a1 knockout mouse with flow cytometry, competitive transplantation, RNA-seq, and pathway western blots\",\n      \"pmids\": [\"36930333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"direct mechanistic link between membrane PS and PTEN regulation not established\", \"single lab\", \"causality versus correlation among pathway changes unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided a computational model of the transport cycle, placing phospholipid binding at the E2P to E2Pi-PL transition and highlighting transmembrane electrostatics.\",\n      \"evidence\": \"Coarse-grained molecular dynamics and binding free energy calculations on the cryo-EM ATP8A1-CDC50 structure\",\n      \"pmids\": [\"36831082\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"computational only, no experimental validation of predicted residues or states\", \"predicted key residues not mutationally tested\", \"model assumes the cryo-EM conformations sampled\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a moonlighting role at the TGN in which the ATP8A1 cytosolic tail stimulates BIG1/BIG2 GEF activity to couple lipid flipping to ARF activation and vesicle coat assembly.\",\n      \"evidence\": \"Reciprocal Co-IP, confocal co-localization, tail-deletion mutagenesis, ARF activation assays, and AP1/GGA2/clathrin recruitment quantification\",\n      \"pmids\": [\"38879142\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"whether GEF stimulation requires catalytic flippase activity untested\", \"single lab\", \"in vivo TGN trafficking consequence not shown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established a late-endosomal function, showing ATP8A1 controls MVB-limiting-membrane PS topology to regulate ESCRT recruitment, ILV cargo sorting, and EGFR signaling.\",\n      \"evidence\": \"siRNA knockdown, GFP-LactC2 PS biosensor, fractionation, cargo trafficking and ESCRT recruitment assays, EGFR western blot\",\n      \"pmids\": [\"40083718\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"mechanism by which luminal-leaflet PS recruits ESCRT not defined\", \"single lab\", \"relationship to AP-3-dependent endosomal sorting not integrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single flippase coordinates its distinct PS- versus PE-flipping activities across plasma membrane, TGN, endosomes, and synaptic vesicles, and how cytosolic-leaflet aminophospholipid changes are transduced into PTEN/YAP/synapsin/ESCRT outputs, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"unified structural basis for substrate switching not established\", \"direct molecular sensors of cytosolic PS/PE in each pathway unidentified\", \"tissue-specific phenotypic hierarchy of ATP8A1 loss not defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [1, 3, 6, 10]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [5, 10]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5, 9, 10]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 10]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [\n      \"ATP8A1-CDC50A flippase complex\"\n    ],\n    \"partners\": [\n      \"CDC50A\",\n      \"BIG1\",\n      \"BIG2\",\n      \"IFT27\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":8,"faith_pct":87.5}}