Insights into the Molecular Properties of ABCA4 and Its Role in the Visual Cycle and Stargardt Disease.

ABCA4 is a member of the A-subfamily of ATP-binding cassette (ABC) transporters localized in rod and cone outer segment disc membranes. Over 800 mutations in ABCA4 are now known to cause Stargardt macular degeneration and related retinal degenerative diseases. Biochemical studies have shown that ABCA4 transports or flips the 11-cis and all-trans isomers of N-retinylidene-phosphatidylethanolamine across disc membranes, thereby facilitating the removal of retinal from disc membranes through the visual cycle and preventing the accumulation of potentially toxic bisretinoid compounds in photoreceptor and retinal pigment epithelial cells. This chapter summarizes studies which have led to our understanding of the role of ABCA4 in the visual cycle and Stargardt disease.