ATP-binding cassette sub-family D member 4 (ABCD4)

ABCD4 is an ATP-binding cassette (ABC) transporter protein of the subfamily D, originally thought to be peroxisomal but now recognized as a lysosomal membrane protein critical for vitamin B12 (cobalamin) metabolism. ABCD4, in association with LMBD1, facilitates the ATP-dependent export of cobalamin from the lysosomal lumen into the cytosol, enabling its subsequent conversion into active cofactors for essential metabolic enzymes. Mutations in ABCD4 result in failure of cobalamin release, leading to rare inherited metabolic disorders characterized by B12 deficiency, with major hematological and neurological consequences. The protein is unique among mammalian ABC transporters for functioning as an importer of a soluble compound into the cytoplasm, contrasting with other members of its subfamily that localize to peroxisomes and mediate fatty acid transport.

Other names

Lysosomal cobalamin transporter ABCD4PXMP1LP70RPXMP1-LPMP69EST352188ATP-binding cassette subfamily D member 4PMP70-related proteinPeroxisomal membrane protein 1-likePeroxisomal membrane protein 69ABC41MAHCJP79R69 kDa peroxisomal ABC transporter

ATPase-dependent translocation of cobalamin across the lysosomal membrane from the lumen to the cytosol