ABCA4

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0001523 retinoid metabolic process	ISS GO_REF:0000024	ACCEPT	Summary: ABCA4 participates in retinal/retinoid handling by moving the retinal-PE adduct to the cytosolic disc leaflet for subsequent retinal release and reduction. Reason: This is a direct transport step in the retinoid metabolic pathway, supported by reconstitution and variant studies. ABCA4 does not itself reduce retinal to retinol or catalyze the chemical cis/trans isomerization. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes.
GO:0001523 retinoid metabolic process	TAS Reactome:R-HSA-2453902	ACCEPT	Summary: ABCA4 participates in retinal/retinoid handling by moving the retinal-PE adduct to the cytosolic disc leaflet for subsequent retinal release and reduction. Reason: This is a direct transport step in the retinoid metabolic pathway, supported by reconstitution and variant studies. ABCA4 does not itself reduce retinal to retinol or catalyze the chemical cis/trans isomerization. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes.
GO:0001750 photoreceptor outer segment	IEA GO_REF:0000120	ACCEPT	Summary: ABCA4 acts in photoreceptor outer-segment disc membranes, particularly at rims and incisures; the rod-disc annotation describes a well-established location. Reason: Disc-membrane localization is consistent with direct NRPE transport and the original rim-protein studies. This annotation does not imply exclusive rod expression: cones and RPE also express ABCA4. Supporting Evidence: PMID:9202155 RmP is expressed specifically in photoreceptors and predominantly in outer segments. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0001750 photoreceptor outer segment	ISS GO_REF:0000024	ACCEPT	Summary: ABCA4 acts in photoreceptor outer-segment disc membranes, particularly at rims and incisures; the rod-disc annotation describes a well-established location. Reason: Disc-membrane localization is consistent with direct NRPE transport and the original rim-protein studies. This annotation does not imply exclusive rod expression: cones and RPE also express ABCA4. Supporting Evidence: PMID:9202155 RmP is expressed specifically in photoreceptors and predominantly in outer segments. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0001750 photoreceptor outer segment	ISS GO_REF:0000024	ACCEPT	Summary: ABCA4 acts in photoreceptor outer-segment disc membranes, particularly at rims and incisures; the rod-disc annotation describes a well-established location. Reason: Disc-membrane localization is consistent with direct NRPE transport and the original rim-protein studies. This annotation does not imply exclusive rod expression: cones and RPE also express ABCA4. Supporting Evidence: PMID:9202155 RmP is expressed specifically in photoreceptors and predominantly in outer segments. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0003924 GTPase activity	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: ABCA4 has experimentally demonstrated GTPase capacity in the bovine ortholog used as the ISS donor. Reason: The WITH/FROM donor is reviewed bovine ABCA4 F1MWM0, whose GTPase IDA points to PMID:10767284. That study directly measured GTP hydrolysis, and PMID:22735453 found GTP could partly replace ATP in transport. Retain this biochemical capacity as non-core because physiological GTP-driven transport in human photoreceptors is not established. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: UniProtKB:F1MWM0 · ABCA4 (Bos taurus) SUPPORTS TRANSFER Live UniProt and QuickGO trace the bovine GTPase IDA to PMID:10767284; its accessible abstract explicitly reports ATPase and GTPase assays. This is supported nucleotidase promiscuity, not a mistaken transfer from a small GTPase. Supporting Evidence: PMID:10767284 We have examined the ATPase and GTPase activity of detergent-solubilized and reconstituted ABCR. PMID:22735453 GTP could partially substitute for ATP, whereas ADP and GDP showed substantially reduced activity.
GO:0005501 retinoid binding	ISS GO_REF:0000024	ACCEPT	Summary: Retinoid binding is integral to the ABCA4 substrate-recognition mechanism. Reason: Purified ABCA4 binds NRPE, and isolated human domains also bind retinal isomers. The broad retinoid-binding term is correct and encompasses this experimentally demonstrated chemistry without making free retinal the principal transported species. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:20404325 we have demonstrated that this domain specifically interacts with all-trans-retinal. PMID:23144455 the nucleotide binding domain 1 (NBD1) specifically bound 11-cis-retinal. PMID:15471866 ABCA4 preferentially binds N-retinylidene-phosphatidylethanolamine with high affinity in the absence of ATP.
GO:0005502 11-cis retinal binding	IDA PMID:23144455 Retinoid binding properties of nucleotide binding domain 1 o...	KEEP AS NON CORE	Summary: An isolated recombinant human NBD1 polypeptide directly binds 11-cis-retinal. Reason: The cited fluorescence-anisotropy experiment supports the binding claim. It does not establish an independent physiological retinal-sequestration function of full-length ABCA4; the primary transport substrate is the retinal-PE adduct. Supporting Evidence: PMID:23144455 the nucleotide binding domain 1 (NBD1) specifically bound 11-cis-retinal.
GO:0005503 all-trans retinal binding	IDA PMID:20404325 Interaction of extracellular domain 2 of the human retina-sp...	KEEP AS NON CORE	Summary: Recombinant human extracellular domain 2 directly interacts with all-trans-retinal. Reason: Fluorescence assays support this domain-level binding capacity. Retain it as ancillary biochemical evidence while distinguishing free-retinal binding from the established full-length NRPE flippase function. Independent evidence in PMID:15471866 also detects some free-retinal binding by purified full-length bovine protein. Supporting Evidence: PMID:20404325 we have demonstrated that this domain specifically interacts with all-trans-retinal.
GO:0005503 all-trans retinal binding	IDA PMID:29847635 Correlating the Expression and Functional Activity of ABCA4 ...	KEEP AS NON CORE	Summary: The cited full-length variant study measures binding of N-retinylidene-PE generated from retinal plus PE, rather than demonstrating free-retinal binding in that assay. Reason: Retain the experimentally supported free-retinal-binding capacity as ancillary to NRPE transport. The cited variant assay measures NRPE recognition and does not independently establish free-retinal binding or leaflet translocation. Free-retinal binding is supported separately by the human ECD2 experiment and by purified full-length bovine ABCA4 in PMID:15471866. This ligand-specific caveat does not justify replacing a binding assertion with flippase activity. Supporting Evidence: PMID:29847635 Binding of N-Ret-PE to ABCA4 variants in the absence and presence of ATP. PMID:20404325 we have demonstrated that this domain specifically interacts with all-trans-retinal. PMID:15471866 0.3 mol of all-trans-retinal were bound in the absence of phosphatidylethanolamine.
GO:0005503 all-trans retinal binding	IDA PMID:33375396 Functional Characterization of ABCA4 Missense Variants Linke...	KEEP AS NON CORE	Summary: The cited full-length variant study measures binding of N-retinylidene-PE generated from retinal plus PE, rather than demonstrating free-retinal binding in that assay. Reason: Retain the experimentally supported free-retinal-binding capacity as ancillary to NRPE transport. The cited variant assay measures NRPE recognition and does not independently establish free-retinal binding or leaflet translocation. Free-retinal binding is supported separately by the human ECD2 experiment and by purified full-length bovine ABCA4 in PMID:15471866. This ligand-specific caveat does not justify replacing a binding assertion with flippase activity. Supporting Evidence: PMID:33375396 ABCA4 immobilized on an immunoaffinity matrix was treated with ATR in the presence of PE to generate N-Ret-PE. PMID:20404325 we have demonstrated that this domain specifically interacts with all-trans-retinal. PMID:15471866 0.3 mol of all-trans-retinal were bound in the absence of phosphatidylethanolamine.
GO:0005524 ATP binding	IEA GO_REF:0000002	ACCEPT	Summary: ABCA4 binds ATP at its two cytoplasmic nucleotide-binding domains to drive conformational cycling. Reason: ATP binding is a core mechanistic component of the importer. Later human cryo-EM and ATPase studies directly corroborate the original sequence-based transporter identification. PMID:34158497 resolves two ATP-Mg2+ molecules in the hydrolysis-deficient human ABCA4QQ construct, separating direct nucleotide binding from ATP turnover. Supporting Evidence: PMID:33605212 The final model contains 2 ATP molecules, 8 lipid molecules, and 1920 residues. PMID:34158497 Two strong and well-defined EM densities were observed for two bound ATP-Mg2+ molecules that were sandwiched between the two NBDs
GO:0005524 ATP binding	TAS PMID:9054934 A photoreceptor cell-specific ATP-binding transporter gene (...	ACCEPT	Summary: ABCA4 binds ATP at its two cytoplasmic nucleotide-binding domains to drive conformational cycling. Reason: ATP binding is a core mechanistic component of the importer. Later human cryo-EM and ATPase studies directly corroborate the original sequence-based transporter identification. PMID:34158497 resolves two ATP-Mg2+ molecules in the hydrolysis-deficient human ABCA4QQ construct, separating direct nucleotide binding from ATP turnover. Supporting Evidence: PMID:33605212 The final model contains 2 ATP molecules, 8 lipid molecules, and 1920 residues. PMID:34158497 Two strong and well-defined EM densities were observed for two bound ATP-Mg2+ molecules that were sandwiched between the two NBDs
GO:0005783 endoplasmic reticulum	IDA GO_REF:0000052	KEEP AS NON CORE	Summary: The Human Protein Atlas reports supported ER staining with antibody HPA064420 in HeLa, MCF-7 and U2OS cells. Reason: The live HPA subcellular record supports this cell-line localization; independent heterologous-expression studies also show some wild-type ER staining. Retain this context-specific location without making ER the principal site of retinal transport in photoreceptors. Supporting Evidence: PMID:29847635 WT ABCA4 showed a punctate staining pattern characteristic of intracellular vesicle-like structures containing calnexin with some evidence of ER reticular staining.
GO:0005783 endoplasmic reticulum	IDA PMID:24097981 Differential phospholipid substrates and directional transpo...	KEEP AS NON CORE	Summary: The 2013 study distinguishes large calnexin-positive vesicles containing wild-type ABCA4 from more pronounced reticular ER retention of some disease variants. Reason: The full text was retrieved and checked. Its strongest ER-retention phenotype concerns misfolded mutants; later wild-type imaging also shows limited ER reticular staining. Retain an expression-context ER location, not a core physiological ER transport role. Supporting Evidence: PMID:24097981 WT ABCA4 was present in large intracellular vesicles that also contained calnexin PMID:29847635 WT ABCA4 showed a punctate staining pattern characteristic of intracellular vesicle-like structures containing calnexin with some evidence of ER reticular staining.
GO:0005783 endoplasmic reticulum	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: ABCA4 can be detected in ER-associated compartments during heterologous expression. Reason: The UniProt location mapping is compatible with wild-type imaging, but ER retention is accentuated by pathogenic misfolding and does not define the normal photoreceptor disc location. Supporting Evidence: PMID:29847635 WT ABCA4 showed a punctate staining pattern characteristic of intracellular vesicle-like structures containing calnexin with some evidence of ER reticular staining.
GO:0005886 plasma membrane	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: ABCA4 localizes to the apical plasma membrane of human fetal and induced-pluripotent-stem-cell-derived RPE. Reason: Direct surface proteomics, membrane fractionation, colocalization and immunogold microscopy corroborate this otherwise broad electronic location. PMID:30397118 instead emphasizes RPE internal membranes, including mouse endolysosomal-marker colocalization. The differing compartments and experimental systems leave the relative surface and internal pools unresolved. Retain the directly demonstrated human RPE surface pool as non-core alongside photoreceptor disc localization; do not infer that all RPE ABCA4 is at the plasma membrane. Supporting Evidence: PMID:36306781 specific apical membrane localization was confirmed by colocalization with a well-known apical membrane marker Na+/K+ ATPase PMID:30397118 ABCA4 also colocalized with the early-endosomal protein Rab5 in RPE cells from wild-type (129/Sv) and Mertk−/− mice
GO:0006869 lipid transport	IBA GO_REF:0000033	ACCEPT	Summary: ABCA4 directly transports the phospholipids NRPE and PE between membrane leaflets. Reason: Lipid transport is a correct conserved core process; the more specific phospholipid-translocation annotation and substrate-specific core functions provide further resolution. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0006869 lipid transport	IEA GO_REF:0000002	ACCEPT	Summary: ABCA4 directly transports the phospholipids NRPE and PE between membrane leaflets. Reason: Lipid transport is a correct conserved core process; the more specific phospholipid-translocation annotation and substrate-specific core functions provide further resolution. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0007601 visual perception	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: ABCA4 supports vision by clearing reactive retinal adducts and maintaining photoreceptor and RPE function. Reason: Visual perception is a broad physiological outcome of retinoid handling. The direct molecular role is lipid flipping rather than photon capture or downstream sensory signal transduction. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes.
GO:0007601 visual perception	TAS PMID:9425888 Retinitis pigmentosa caused by a homozygous mutation in the ...	UNDECIDED	Summary: The cited short 1998 disease report concerns an ABCR-associated retinal degeneration, but the cached record has no abstract or full text. Reason: The source cannot be adjudicated directly. ABCA4 clearly supports vision through retinoid handling, but that general knowledge is insufficient to reconstruct what the cited report establishes about the visual-perception annotation.
GO:0007603 phototransduction, visible light	TAS PMID:9202155 The photoreceptor rim protein is an ABC transporter encoded ...	MARK AS OVER ANNOTATED	Summary: The complete 1997 article establishes rim-protein identity and localization, while presenting ion transport and photoresponse functions as unresolved hypotheses. Reason: The original Wiley full text, documented in the prior primary-source access receipt in the notes and reread in the publisher HTML/PDF, leaves the rim protein function unresolved. The present cache remains abstract-only; the short full-text excerpt is separately attributed below. Its discussion speculates about calcium handling and light-stimulated ATPase activity; it does not establish that ABCA4 converts absorbed photons into a molecular signal. Later direct experiments identify NRPE and PE transport supporting retinoid clearance. Thus the legacy phototransduction assignment exceeds the demonstrated role, although ABCA4 contributes to the maintenance of vision. Supporting Evidence: PMID:9202155 may play a role in the photoresponse. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0015850 organic hydroxy compound transport	IEA GO_REF:0000117	MODIFY	Summary: The alcohol/retinol transport description misidentifies the chemical substrate: ABCA4 flips retinal-conjugated PE and PE. Reason: The live GO definitions specify an organic alcohol or retinol. Direct transport assays found no ATP-dependent all-trans-retinol transfer. Replace this with phospholipid translocation; retinal reduction to retinol is performed downstream by RDH enzymes. Proposed replacements: phospholipid translocation Supporting Evidence: PMID:22735453 ATP-dependent transfer was not observed for [3H]-all-trans retinol PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0016020 membrane	EXP PMID:10075733 Retinal stimulates ATP hydrolysis by purified and reconstitu...	ACCEPT	Summary: ABCA4 is a multipass integral membrane transporter. Reason: The broad membrane location is accurate across disc membranes and additional experimentally observed cell-type or expression-system locations; it does not require narrowing all contexts to a single compartment. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:36306781 specific apical membrane localization was confirmed by colocalization with a well-known apical membrane marker Na+/K+ ATPase
GO:0016020 membrane	IEA GO_REF:0000120	ACCEPT	Summary: ABCA4 is a multipass integral membrane transporter. Reason: The broad membrane location is accurate across disc membranes and additional experimentally observed cell-type or expression-system locations; it does not require narrowing all contexts to a single compartment. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:36306781 specific apical membrane localization was confirmed by colocalization with a well-known apical membrane marker Na+/K+ ATPase
GO:0016020 membrane	TAS PMID:9054934 A photoreceptor cell-specific ATP-binding transporter gene (...	ACCEPT	Summary: ABCA4 is a multipass integral membrane transporter. Reason: The broad membrane location is accurate across disc membranes and additional experimentally observed cell-type or expression-system locations; it does not require narrowing all contexts to a single compartment. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:36306781 specific apical membrane localization was confirmed by colocalization with a well-known apical membrane marker Na+/K+ ATPase
GO:0016887 ATP hydrolysis activity	EXP PMID:33605212 Molecular structures of the eukaryotic retinal importer ABCA...	ACCEPT	Summary: ATP hydrolysis is directly measured for ABCA4 and supplies the energy for lipid flipping. Reason: Retain this intrinsic core activity. Basal hydrolysis and NRPE-stimulated hydrolysis are measured separately in biochemical studies; the transporter core functions capture the coupled physiological reaction. Supporting Evidence: PMID:33605212 Basal ATPase activity measured in 0.06% digitonin at 28°C.
GO:0016887 ATP hydrolysis activity	EXP PMID:39128720 Structural and functional characterization of the nucleotide...	ACCEPT	Summary: ATP hydrolysis is directly measured for ABCA4 and supplies the energy for lipid flipping. Reason: Retain this intrinsic core activity. Basal hydrolysis and NRPE-stimulated hydrolysis are measured separately in biochemical studies; the transporter core functions capture the coupled physiological reaction. Supporting Evidence: PMID:39128720 The basal ATPase activity of WT ABCA4 exhibited Michaelis–Menten kinetics while the EQ double mutant was devoid of activity
GO:0016887 ATP hydrolysis activity	IDA PMID:29847635 Correlating the Expression and Functional Activity of ABCA4 ...	ACCEPT	Summary: ATP hydrolysis is directly measured for ABCA4 and supplies the energy for lipid flipping. Reason: Retain this intrinsic core activity. Basal hydrolysis and NRPE-stimulated hydrolysis are measured separately in biochemical studies; the transporter core functions capture the coupled physiological reaction. Supporting Evidence: PMID:29847635 The ATPase activity of immunopurified and reconstituted ABCA4 variants was measured in the presence or absence of all-trans retinal.
GO:0016887 ATP hydrolysis activity	IDA PMID:33375396 Functional Characterization of ABCA4 Missense Variants Linke...	ACCEPT	Summary: ATP hydrolysis is directly measured for ABCA4 and supplies the energy for lipid flipping. Reason: Retain this intrinsic core activity. Basal hydrolysis and NRPE-stimulated hydrolysis are measured separately in biochemical studies; the transporter core functions capture the coupled physiological reaction. Supporting Evidence: PMID:33375396 The ATPase activity of detergent-solubilized WT ABCA4 and disease-associated variants was measured in the absence and presence of all-trans retinal (ATR).
GO:0016887 ATP hydrolysis activity	IEA GO_REF:0000120	ACCEPT	Summary: ATP hydrolysis is directly measured for ABCA4 and supplies the energy for lipid flipping. Reason: Retain this intrinsic core activity. Basal hydrolysis and NRPE-stimulated hydrolysis are measured separately in biochemical studies; the transporter core functions capture the coupled physiological reaction. Supporting Evidence: PMID:39128720 The basal ATPase activity of WT ABCA4 exhibited Michaelis–Menten kinetics while the EQ double mutant was devoid of activity PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0016887 ATP hydrolysis activity	ISS GO_REF:0000024	ACCEPT	Summary: ATP hydrolysis is directly measured for ABCA4 and supplies the energy for lipid flipping. Reason: Retain this intrinsic core activity. Basal hydrolysis and NRPE-stimulated hydrolysis are measured separately in biochemical studies; the transporter core functions capture the coupled physiological reaction. Supporting Evidence: PMID:39128720 The basal ATPase activity of WT ABCA4 exhibited Michaelis–Menten kinetics while the EQ double mutant was devoid of activity PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0031410 cytoplasmic vesicle	IDA PMID:29847635 Correlating the Expression and Functional Activity of ABCA4 ...	KEEP AS NON CORE	Summary: Wild-type ABCA4 accumulates in intracellular vesicle-like structures in heterologous cells. Reason: This is an experimentally documented location in the cited expression assays, distinct from a claim that unspecified cytoplasmic vesicles are the principal physiological site in photoreceptors. RPE studies independently support additional internal-membrane expression. Supporting Evidence: PMID:29847635 WT ABCA4 showed a punctate staining pattern characteristic of intracellular vesicle-like structures containing calnexin with some evidence of ER reticular staining.
GO:0031410 cytoplasmic vesicle	IDA PMID:33375396 Functional Characterization of ABCA4 Missense Variants Linke...	KEEP AS NON CORE	Summary: Wild-type ABCA4 accumulates in intracellular vesicle-like structures in heterologous cells. Reason: This is an experimentally documented location in the cited expression assays, distinct from a claim that unspecified cytoplasmic vesicles are the principal physiological site in photoreceptors. RPE studies independently support additional internal-membrane expression. Supporting Evidence: PMID:33375396 can exit the ER and accumulate in vesicle-like structures similar to WT ABCA4
GO:0031410 cytoplasmic vesicle	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: Wild-type ABCA4 accumulates in intracellular vesicle-like structures in heterologous cells. Reason: This is an experimentally documented location in the cited expression assays, distinct from a claim that unspecified cytoplasmic vesicles are the principal physiological site in photoreceptors. RPE studies independently support additional internal-membrane expression. Supporting Evidence: PMID:29847635 WT ABCA4 showed a punctate staining pattern characteristic of intracellular vesicle-like structures containing calnexin with some evidence of ER reticular staining.
GO:0034632 retinol transmembrane transporter activity	TAS Reactome:R-HSA-1467466	MODIFY	Summary: The Reactome event describes retinal or NRPE handling, but the assigned GO term denotes retinol, the corresponding alcohol. Reason: Direct reconstitution demonstrates NRPE flipping and explicitly found no ATP-dependent retinol transfer. Replace the chemically mismatched retinol transporter term with NRPE flippase activity; the disease reaction does not make retinol a wild-type substrate. Proposed replacements: N-retinylidene-phosphatidylethanolamine flippase activity Supporting Evidence: PMID:22735453 ATP-dependent transfer was not observed for [3H]-all-trans retinol PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0034632 retinol transmembrane transporter activity	TAS Reactome:R-HSA-2466802	MODIFY	Summary: The Reactome event describes retinal or NRPE handling, but the assigned GO term denotes retinol, the corresponding alcohol. Reason: Direct reconstitution demonstrates NRPE flipping and explicitly found no ATP-dependent retinol transfer. Replace the chemically mismatched retinol transporter term with NRPE flippase activity; the disease reaction does not make retinol a wild-type substrate. Proposed replacements: N-retinylidene-phosphatidylethanolamine flippase activity Supporting Evidence: PMID:22735453 ATP-dependent transfer was not observed for [3H]-all-trans retinol PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0034633 retinol transport	IEA GO_REF:0000108	MODIFY	Summary: The alcohol/retinol transport description misidentifies the chemical substrate: ABCA4 flips retinal-conjugated PE and PE. Reason: The live GO definitions specify an organic alcohol or retinol. Direct transport assays found no ATP-dependent all-trans-retinol transfer. Replace this with phospholipid translocation; retinal reduction to retinol is performed downstream by RDH enzymes. Proposed replacements: phospholipid translocation Supporting Evidence: PMID:22735453 ATP-dependent transfer was not observed for [3H]-all-trans retinol PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0042574 retinal metabolic process	IDA PMID:29847635 Correlating the Expression and Functional Activity of ABCA4 ...	ACCEPT	Summary: ABCA4 participates in retinal/retinoid handling by moving the retinal-PE adduct to the cytosolic disc leaflet for subsequent retinal release and reduction. Reason: This is a direct transport step in the retinoid metabolic pathway, supported by reconstitution and variant studies. ABCA4 does not itself reduce retinal to retinol or catalyze the chemical cis/trans isomerization. Supporting Evidence: PMID:29847635 Binding of N-Ret-PE to ABCA4 variants in the absence and presence of ATP. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0042574 retinal metabolic process	IDA PMID:33375396 Functional Characterization of ABCA4 Missense Variants Linke...	ACCEPT	Summary: ABCA4 participates in retinal/retinoid handling by moving the retinal-PE adduct to the cytosolic disc leaflet for subsequent retinal release and reduction. Reason: This is a direct transport step in the retinoid metabolic pathway, supported by reconstitution and variant studies. ABCA4 does not itself reduce retinal to retinol or catalyze the chemical cis/trans isomerization. Supporting Evidence: PMID:33375396 ABCA4 immobilized on an immunoaffinity matrix was treated with ATR in the presence of PE to generate N-Ret-PE. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0042574 retinal metabolic process	ISS GO_REF:0000024	ACCEPT	Summary: ABCA4 participates in retinal/retinoid handling by moving the retinal-PE adduct to the cytosolic disc leaflet for subsequent retinal release and reduction. Reason: This is a direct transport step in the retinoid metabolic pathway, supported by reconstitution and variant studies. ABCA4 does not itself reduce retinal to retinol or catalyze the chemical cis/trans isomerization. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes.
GO:0042626 ATPase-coupled transmembrane transporter activity	IBA GO_REF:0000033	ACCEPT	Summary: The PAINT ATPase-coupled transporter assertion correctly captures the conserved transport mechanism. Reason: Human ABCA4 directly couples ATP use to lipid movement. The conservative ancestral annotation remains valid; specific lipid-carrier and flippase terms express the target-level substrate and direction. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0042626 ATPase-coupled transmembrane transporter activity	TAS PMID:9054934 A photoreceptor cell-specific ATP-binding transporter gene (...	ACCEPT	Summary: The cloning study identified ABCA4 as an ATP-binding cassette transporter; later biochemical work directly verifies ATP-coupled transport. Reason: This conservative mechanism-level term is valid across NRPE and PE substrates. Specific lipid-carrier and flippase terms already capture the substrate and leaflet direction; the broad transporter activity is not a separate core function. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0045332 phospholipid translocation	IDA PMID:24097981 Differential phospholipid substrates and directional transpo...	ACCEPT	Summary: ABCA4 catalyzes ATP-dependent movement of NRPE and PE between membrane leaflets. Reason: Phospholipid translocation directly describes the work of the enzyme, with inward movement from exoplasmic/lumenal to cytosolic leaflet. This is a core process supported by purified-protein transport assays. Supporting Evidence: PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0045332 phospholipid translocation	IEA GO_REF:0000117	ACCEPT	Summary: ABCA4 catalyzes ATP-dependent movement of NRPE and PE between membrane leaflets. Reason: Phospholipid translocation directly describes the work of the enzyme, with inward movement from exoplasmic/lumenal to cytosolic leaflet. This is a core process supported by purified-protein transport assays. Supporting Evidence: PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0055085 transmembrane transport	IEA GO_REF:0000002	MODIFY	Summary: The transport performed by ABCA4 is phospholipid translocation between the two membrane leaflets. Reason: The specific phospholipid-translocation process captures the experimentally demonstrated work of ABCA4 more precisely than general transmembrane transport. Proposed replacements: phospholipid translocation Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0055085 transmembrane transport	TAS Reactome:R-HSA-382556	MODIFY	Summary: The transport performed by ABCA4 is phospholipid translocation between the two membrane leaflets. Reason: The specific phospholipid-translocation process captures the experimentally demonstrated work of ABCA4 more precisely than general transmembrane transport. Proposed replacements: phospholipid translocation Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0090555 phosphatidylethanolamine flippase activity	IDA PMID:24097981 Differential phospholipid substrates and directional transpo...	ACCEPT	Summary: Purified ABCA4 actively flips PE from the exoplasmic to the cytosolic leaflet. Reason: The cited comparative study directly assays phospholipid transport and distinguishes inward PE movement by ABCA4 from outward movement by ABCA1 and ABCA7. This is an intrinsic core activity in addition to NRPE transport. Supporting Evidence: PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0097381 photoreceptor disc membrane	TAS Reactome:R-HSA-1467466	ACCEPT	Summary: ABCA4 acts in photoreceptor outer-segment disc membranes, particularly at rims and incisures; the rod-disc annotation describes a well-established location. Reason: Disc-membrane localization is consistent with direct NRPE transport and the original rim-protein studies. This annotation does not imply exclusive rod expression: cones and RPE also express ABCA4. Supporting Evidence: PMID:9202155 RmP is expressed specifically in photoreceptors and predominantly in outer segments. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0097381 photoreceptor disc membrane	TAS Reactome:R-HSA-2466802	ACCEPT	Summary: ABCA4 acts in photoreceptor outer-segment disc membranes, particularly at rims and incisures; the rod-disc annotation describes a well-established location. Reason: Disc-membrane localization is consistent with direct NRPE transport and the original rim-protein studies. This annotation does not imply exclusive rod expression: cones and RPE also express ABCA4. Supporting Evidence: PMID:9202155 RmP is expressed specifically in photoreceptors and predominantly in outer segments. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0120202 rod photoreceptor disc membrane	ISS GO_REF:0000024	ACCEPT	Summary: ABCA4 acts in photoreceptor outer-segment disc membranes, particularly at rims and incisures; the rod-disc annotation describes a well-established location. Reason: Disc-membrane localization is consistent with direct NRPE transport and the original rim-protein studies. This annotation does not imply exclusive rod expression: cones and RPE also express ABCA4. Supporting Evidence: PMID:9202155 RmP is expressed specifically in photoreceptors and predominantly in outer segments. PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes
GO:0140326 ATPase-coupled intramembrane lipid carrier activity	EXP PMID:24097981 Differential phospholipid substrates and directional transpo...	ACCEPT	Summary: ATP-driven intramembrane lipid carrying accurately describes the common mechanism for ABCA4 transport of NRPE and PE. Reason: The term covers leaflet-to-leaflet translocation without conflating free retinol with retinal-phospholipid adducts. Both substrates have direct reconstitution evidence. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0140326 ATPase-coupled intramembrane lipid carrier activity	IBA GO_REF:0000033	ACCEPT	Summary: ATP-driven intramembrane lipid carrying accurately describes the common mechanism for ABCA4 transport of NRPE and PE. Reason: The term covers leaflet-to-leaflet translocation without conflating free retinol with retinal-phospholipid adducts. Both substrates have direct reconstitution evidence. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0140326 ATPase-coupled intramembrane lipid carrier activity	IEA GO_REF:0000120	ACCEPT	Summary: ATP-driven intramembrane lipid carrying accurately describes the common mechanism for ABCA4 transport of NRPE and PE. Reason: The term covers leaflet-to-leaflet translocation without conflating free retinol with retinal-phospholipid adducts. Both substrates have direct reconstitution evidence. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0140327 flippase activity	IDA PMID:24097981 Differential phospholipid substrates and directional transpo...	MODIFY	Summary: The cited 2013 experiment identifies PE as the lipid flipped inward by ABCA4. Reason: Refine the generic directional flippase term to PE flippase activity, which retains the measured exoplasmic-to-cytosolic direction and specifies the substrate assayed. Proposed replacements: phosphatidylethanolamine flippase activity Supporting Evidence: PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.
GO:0140347 N-retinylidene-phosphatidylethanolamine flippase activity	EXP PMID:22735453 ABCA4 is an N-retinylidene-phosphatidylethanolamine and phos...	ACCEPT	Summary: ABCA4 flips N-retinylidene-PE from the disc lumenal leaflet to the cytosolic leaflet, enabling clearance of all-trans and excess 11-cis retinal. Reason: The GO label matches the direct substrate-specific transport experiments. Its live text definition unexpectedly names the doubly retinylated compound N-retinylidene-N-retinylphosphatidylethanolamine; this apparent definition defect is recorded as an expert question, not used to replace the source identifier or infer bisretinoid transport. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes. PMID:36931393 N-Ret-PS is not a substrate for ABCA4 PMID:34625547 WT ABCA4 displayed significant ATP-dependent N-Ret-PE transport activity as previously reported7,18, whereas all variants showed significantly reduced transport activity
GO:0140347 N-retinylidene-phosphatidylethanolamine flippase activity	IEA GO_REF:0000120	ACCEPT	Summary: ABCA4 flips N-retinylidene-PE from the disc lumenal leaflet to the cytosolic leaflet, enabling clearance of all-trans and excess 11-cis retinal. Reason: The GO label matches the direct substrate-specific transport experiments. Its live text definition unexpectedly names the doubly retinylated compound N-retinylidene-N-retinylphosphatidylethanolamine; this apparent definition defect is recorded as an expert question, not used to replace the source identifier or infer bisretinoid transport. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes. PMID:36931393 N-Ret-PS is not a substrate for ABCA4 PMID:34625547 WT ABCA4 displayed significant ATP-dependent N-Ret-PE transport activity as previously reported7,18, whereas all variants showed significantly reduced transport activity
GO:0140347 N-retinylidene-phosphatidylethanolamine flippase activity	ISS GO_REF:0000024	ACCEPT	Summary: ABCA4 flips N-retinylidene-PE from the disc lumenal leaflet to the cytosolic leaflet, enabling clearance of all-trans and excess 11-cis retinal. Reason: The GO label matches the direct substrate-specific transport experiments. Its live text definition unexpectedly names the doubly retinylated compound N-retinylidene-N-retinylphosphatidylethanolamine; this apparent definition defect is recorded as an expert question, not used to replace the source identifier or infer bisretinoid transport. Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24707049 ABCA4 can transport N-11-cis-retinylidene-phosphatidylethanolamine (PE), the Schiff-base conjugate of 11-cis-retinal and PE, from the lumen to the cytoplasmic leaflet of disk membranes. PMID:36931393 N-Ret-PS is not a substrate for ABCA4 PMID:34625547 WT ABCA4 displayed significant ATP-dependent N-Ret-PE transport activity as previously reported7,18, whereas all variants showed significantly reduced transport activity
GO:0140359 ABC-type transporter activity	IEA GO_REF:0000002	MODIFY	Summary: ABCA4 is an ABC-type ATP-dependent lipid importer with defined intramembrane substrates. Reason: Refine the generic family activity to ATPase-coupled intramembrane lipid carrier activity, covering NRPE and PE while preserving the ABC mechanism. Proposed replacements: ATPase-coupled intramembrane lipid carrier activity Supporting Evidence: PMID:22735453 ABCA4 functions as a novel N-retinylidene-PE and PE importer translocating these substrates from the lumen to the cytoplasmic side of photoreceptor disc membranes PMID:24097981 In contrast, ABCA4 transported phosphatidylethanolamine in the reverse direction.

Gene Description

Existing Annotations Review

Core Functions

Uses ATP hydrolysis to flip N-retinylidene-phosphatidylethanolamine from the lumenal to the cytosolic leaflet of photoreceptor disc membranes, facilitating clearance of all-trans and excess 11-cis retinal.

Uses ATP hydrolysis to flip phosphatidylethanolamine from the exoplasmic/lumenal to the cytosolic membrane leaflet. This substrate activity is directly demonstrated alongside NRPE transport.

References

Suggested Questions for Experts

Deep Research

Falcon

📚 Additional Documentation

Notes

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