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I. Introduction

EmrM is a prototype of the Small Multi-drug Resistance family of efflux transporters and actively expels positively charged hydrophobic drugs across the inner membrane of Escherichia coli.

For more information see Biochemistry Online: Chapter 9A - Energy Transduction: Uses of ATP

II. General Structure

Backbone and sidechains
Cartoon, Hbonds and Wireframe
Two EmrE polypeptides form a homodimeric transporter that binds substrate (tetraphenylphosphonium, TPP) at the dimerization interface.
Wireframe with Leu-7, Tyr-60, and Trp-63 spacefilled and TPP cartoon

Leu-7, Tyr-60, and Trp-63 are residues that are important for drug transport because they perform essential structural roles.
Cartoon with Glu-14 spacefilled and TPP cartoon

TPP first binds to Glu-14 in one subunit of the dimer in exchange for a proton.