Abstract
Human ATP-binding cassette (ABC) transporter ABCD1 transports CoA esters of saturated/monounsaturated very long chain fatty acid from cytosol to the peroxisome for β-oxidation. Dysfunction of human ABCD1 usually causes the severe progressive genetic disorder X-linked adrenoleukodystrophy, which eventually affects the adrenal glands and/or the central nervous system. Here, we report three cryo-EM structures of human ABCD1 in various states. The apo-form ABCD1 at 3.53 Å resolution adopts an inward-facing conformation, harboring a phosphatidyl ethanolamine (PE) molecule at each lateral entry of substrate cavity. In the substrate-bound ABCD1 structure at 3.59 Å resolution, two molecules of C22:0-CoA (one of the physiological substrates of ABCD1) is symmetrically bound to the transmembrane domains (TMDs). Each C22:0-CoA adopts an unpresented L-shape configuration: the CoA portion inserts into a polar pocket at the TMD at a pose parallel to the membrane plane, whereas the acyl chain portion perpendicular to membrane plane is embedded in a hydrophobic pocket at the opposite TMD. Upon binding the two C22:0-CoA molecules, which resemble a pair of hinges crossing the two TMDs, the two nucleotide-binding domains (NBDs) of ABCD1 approach towards each other. Addition ATP to the substrate-bound ABCD1 enabled us to reveal an ATP-bound structure at 2.79 Å, which shows an outward-facing conformation with the dimerized NBDs succeeding substrate release. These three structures combined with biochemical assays exhibit a snapshot of ABCD1-mediated substrate recognition, translocation and release. These findings provide the structural insights into the transport mechanism of ABC transporters that transport amphipathic molecules with long acyl chains.
Competing Interest Statement
The authors have declared no competing interest.