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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
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.