Small is mighty: EmrE, a multidrug transporter as an experimental paradigm

EmrE is a multidrug transporter from Escherichia coli that functions as a h omooligomer and is unique in ifs small size. In each monomer there are four tightly packed transmembrane segments and one membrane-embedded charged re sidue. This residue provides the basis for the coupling mechanism as part o f a binding site "time shared" by substrates and protons.