Structural insights into human ABCA7-mediated lipid transport

The human ATP-binding cassette (ABC) transporter ABCA7 participates in the lipidation of apolipoprotein ApoE, a commonly recognized risk factor for Alzheimer's disease (AD). How ABCA7 is involved in the molecular pathogenesis of AD remains poorly understood. Using cryoelectron microscopy (cryo-EM), we determined ABCA7 structures in the apo and substrate-bound forms, respectively. Combined with activity assays, we assigned the residues that specifically bind two molecules of phosphatidylserine (PS) that are arranged in a "tail-to-tail" manner. Pull-down assays confirmed that ApoE directly interacts with ABCA7; and moreover, both ATPase and lipid transport activities of ABCA7 were significantly enhanced in the presence of ApoE. We also measured the activities of a familial AD variant and a protective clinically reported variant in the ABCA7 gene. Our findings not only give structural insights into ABCA7-mediated PS translocation, but we also provide first biochemical evidence for its link to AD by forwarding lipids to ApoE.