Structure of the multidrug resistance efflux transporter EmrE from Escherichia coli

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Abstract
Multidrug resistance efflux transporters threaten to reverse the progress treating infectious disease by extruding a wide range of drug and other cytotoxic compounds. One such drug transporter, EmrE, from the small multidrug resistance family, utilizes proton gradients as an energy source to drive substrate translocation. In an effort to understand the molecular structural basis of this transport mechanism, we have determined the structure of EmrE from Escherichia coli to 3.8 A. EmrE is a tetramer comprised of two conformational heterodimers related by a pseudo two-fold symmetry axis perpendicular to the cell membrane. Based on the structure and biochemical evidence, we propose a mechanism by which EmrE accomplishes multidrug efflux by coupling conformational changes between two heterodimers with proton gradient. Because of its simplicity and compact size, the structure of EmrE can serve as an ideal model for understanding the general structural basis of proton:drug antiport for other drug efflux systems.