Abstract
Multidrug and toxic compound extrusion (MATE) transporters contribute to multidrug resistance by coupling the efflux of drugs to the influx of Na(+) or H(+). Known structures of Na(+)-coupled, extracellular-facing MATE transporters from the NorM subfamily revealed 12 membrane-spanning segments related by a quasi-two-fold rotational symmetry and a multidrug-binding cavity situated near the membrane surface. Here we report the crystal structure of an H(+)-coupled MATE transporter from Bacillus halodurans and the DinF subfamily at 3.2-Å resolution, unveiling a surprisingly asymmetric arrangement of 12 transmembrane helices. We also identified a membrane-embedded substrate-binding chamber by combining crystallographic and biochemical analyses. Our studies further suggested a direct competition between H(+) and substrate during DinF-mediated transport and implied how a MATE transporter alternates between its extracellular- and intracellular-facing conformations to propel multidrug extrusion. Collectively, our results demonstrated heretofore-unrecognized mechanistic diversity among MATE transporters.