Evidence for a Molecular Diode-based Mechanism in a Multi-specific ABC Exporter: Ser-1368 as a Gatekeeping Residue in the Yeast Multidrug Transporter Pdr5 [Microbiology]
August 11th, 2014 by Mehla, J., Ernst, R., Moore, R., Wakschlag, A., Marquis, M. K., Ambudkar, S. V., Golin, J.
ABC multidrug efflux pumps transport a wide range of substrates. Current models suggest that a drug binds relatively tightly to a transport site in the transmembrane domains when the protein is in the closed inward-facing conformation. Upon binding of ATP, the transporter can switch to an outward-facing (drug off or drug releasing) structure of lower affinity. ATP hydrolysis is critically important for remodeling the drug-binding site to facilitate drug release and to reset the transporter for a new transport cycle. We characterized the novel phenotype of an S1368A mutant which that lies in the putative drug-binding pocket of the yeast multidrug transporter Pdr5. This substitution created broad, severe drug hypersensitivity, although drug binding, ATP hydrolysis, and intradomain signaling were indistinguishable from the wild-type control. Several different rhodamine 6G transport assays yielded evidence consistent with the possibility that Ser-1368 prevents reentry of the excluded drug.