ATP-binding cassette sub-family A member 4 (ABCA4) (ABCA4)

ATP-binding cassette sub-family A member 4 (ABCA4) is a crucial transmembrane protein located in the outer segment disc membranes of rod and cone photoreceptor cells. It functions as an ATP-driven flippase, transporting N-retinylidene-phosphatidylethanolamine from the intradiscal to the cytoplasmic leaflet, which is a vital step in the visual cycle for recycling vitamin A derivatives (UniProt P78363). Deficiencies in ABCA4 lead to the accumulation of toxic lipofuscin precursors, such as A2E, within the retinal pigment epithelium (RPE), eventually causing cell death and vision loss. Mutations in the ABCA4 gene are the primary cause of Stargardt disease (STGD1) and are significantly associated with other retinal dystrophies including cone-rod dystrophy and age-related macular degeneration (PubMed: 29335243). Current therapeutic development focuses on gene replacement therapies to restore protein function and small molecule inhibitors, like Tinlarebant, designed to reduce the metabolic load on the visual cycle (ClinicalTrials.gov: NCT05244304). Additionally, deuterated vitamin A (ALK-001) is being investigated to slow the dimerization of retinal into toxic aggregates. As a central gatekeeper of retinal metabolic health, ABCA4 remains a primary target for treating inherited macular degenerations.

Other names

ABCRRim proteinPhotoreceptor-specific ATP-binding cassette transporterStargardt disease protein 1ABC10

ABCA4 acts as an ATP-dependent flippase that moves N-retinylidene-phosphatidylethanolamine (N-ret-PE) from the inner (lumenal) leaflet to the outer (cytoplasmic) leaflet of the disc membrane in photoreceptor cells (UniProt P78363). This activity facilitates the removal of all-trans-retinal from the disc, preventing its spontaneous reaction with phosphatidylethanolamine to form toxic bis-retinoids like A2E (PubMed: 10611235).