The SMR family: a novel family of multidrug efflux proteins involved with the efflux of lipophilic drugs

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Abstract
Summary: The sequenced members of a novel family of small, hydrophobic, bacterial multidrug‐resistance efflux proteins, which we have designated the small multidrug resistance (SMR) protein family, are identified and analysed. Two distinct clusters of proteins were identified within this family: (i) small multidrug efflux systems; and (ii) Sug proteins, potentially involved in the suppression of groEL mutations. Hydropathy and residue distribution analyses of this family suggest a structural model in which the polypeptide chain spans the membrane four times as mildly amphipathic α‐helices. The roles of specific residues, a possible mechanistic model of drug efflux, and the primary physiological role(s) of the SMR proteins are discussed.