title: Small multidrug resistance proteins: a multidrug transporter family that continues to grow.
abstract: The small multidrug resistance (SMR) protein family is a bacterial multidrug transporter family. As suggested by their title, SMR proteins are composed of four transmembrane alpha-helices of approximately 100-140 amino acids in length. Since their designation as a family, many homologues have been identified and characterized both structurally and functionally. In this review the topology, structure, drug resistance, drug binding, and transport mechanisms of the entire SMR protein family are examined. Additionally, updated bioinformatic analysis of predicted and characterized SMR protein family members was also conducted. Based on SMR sequence alignments and phylogenetic analysis of current members, we propose that this small multidrug resistance transporter family should be expanded into three subclasses: (i) the small multidrug pumps (SMP), (ii) suppressor of groEL mutation proteins (SUG), and a third group (iii) paired small multidrug resistance proteins (PSMR). The roles of these three SMR subclasses are examined, and the well-characterized members, such as Escherichia coli EmrE and SugE, are described in terms of their function and structural organization.
authors.affiliation: Biological Sciences Building, Department of Biological Sciences, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada T2N 1N4.
authors.forename: Denice C
authors.initials: DC
authors.lastname: Bay
authors.forename: Kenton L
authors.initials: KL
authors.lastname: Rommens
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Turner
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000737:chemistry / Q000145:classification* / Q000378:metabolism / Q000502:physiology*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D019281:Dimerization; D008954:Models, Biological; D008958:Models, Molecular; D008970:Molecular Weight; D010802:Phylogeny
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D017920:Antiporters; D001426:Bacterial Proteins; D018834:Chaperonin 60