ABCA4

Retinal-specific phospholipid-transporting ATPase ABCA4

Flippase that catalyzes in an ATP-dependent manner the transport of retinal-phosphatidylethanolamine conjugates like 11-cis and all-trans isomers of N-retinylidene-phosphatidylethanolamine (N-Ret-PE) from the lumen to the cytoplasmic leaflet of photoreceptor outer segment disk membranes, where 11-cis-retinylidene-phosphatidylethanolamine is then isomerized to its all-trans isomer and reduced by RDH8 to produce all-trans-retinol. This transport activity ensures that all-trans-retinal generated from photoexcitation and 11-cis-retinal not needed for the regeneration of rhodopsin and cone opsins are effectively cleared from the photoreceptors, therefore preventing their accumulation and the formation of toxic bisretinoid (PubMed:10075733, PubMed:20404325, PubMed:22735453, PubMed:23144455, PubMed:24097981, PubMed:29847635, PubMed:33375396). Displays ATPase activity in vitro in absence of retinal substrate (PubMed:33605212, PubMed:39128720, PubMed:29847635, PubMed:33375396). May display GTPase activity that is strongly influenced by the lipid environment and the presence of retinoid compounds (PubMed:22735453). Binds the unprotonated form of N-retinylidene-phosphatidylethanolamine with high affinity in the absence of ATP, and ATP binding and hydrolysis induce a protein conformational change that causes N-retinylidene-phosphatidylethanolamine release (By similarity)