Novel features in the structure of P-glycoprotein (ABCB1) in the post-hydrolytic state as determined at 7.9Å resolution

Abstract

P-glycoprotein (ABCB1) is a ATP-binding cassette transporter that plays an important role in the removal of drugs and xenobiotic compounds from the cell.It is also associated with multi-drug resistance in cancer. Here we report novel features of the cryo-EM-derived structure of P-glycoprotein in the posthydrolytic state: The cytosolic nucleotide-binding domains (NBDs) are separated despite ADP remaining bound to the NBDs. Gaps in the TMDs that connect to the inner hydrophilic cavity are back-filled by detergent head-groups from the annular detergent micelle and are close to two regions predicted to delineate two pseudo-symmetry-related drug-binding sites. In this conformation, the (newly-resolved) N-terminal extension, NBD-TMD linker region and gap-filling detergents all appear to impede NBD dimerisation. We propose a model for the mechanism of action of the exporter where ATP will be bound to the protein for most of the time, consistent with the high physiological ATP concentrations in vivo. KeywordsP-glycoprotein; ABCB1; ATP-binding cassette; transporter, membrane protein, protein structure, cryo-electron microscopy.

Does human P-glycoprotein efflux involve transmembrane alpha helix breakage?

“…When reporting only to the cryo-EM structures, both inward murine (PDB ID: 6GDI) and outward human (PDB ID: 6C0V) were found to have both TM4/TM10 modelled as straight helices. Furthermore, while Thongin and co-workers identified electron densities compatible with “detergent head-groups from the annular detergent micelle (…) close to two regions predicted to delineate two pseudo-symmetry-related drug-binding sites” but no TM4/TM10 kink [5], other authors reported for the outward-facing human structure that the “continuity of these helices is important to completely close the intracellular gate upon NBD dimerization, avoiding potential leakage in the outward-facing state” [2]. So, what could be the underlying reason for such a difference?…”