Transmembrane helix 6 of ABCD4 is indispensable for cobalamin transport.

ABCD4, which belongs to the ABC protein subfamily D, plays a role in the transport of cobalamin from lysosomes to the cytosol by cooperating with ATP-binding and ATP-hydrolysis. Pathogenic variants in the ABCD4 gene lead to an inherited metabolic disorder characterized by cobalamin deficiency. However, the structural requirements for cobalamin transport in ABCD4 remain unclear.