title: KtrB, a member of the superfamily of K+ transporters.
abstract: KtrB is the K(+)-translocating subunit of the K(+)-uptake system KtrAB from bacteria. It is a member of the superfamily of K(+)transporters (SKT proteins) with other sub-families occurring in archaea, bacteria, fungi, plants and trypanosomes. SKT proteins may have originated from small K(+) channels by at least two gene duplication and two gene fusion events. They contain four covalently linked M(1)PM(2) domains, in which M(1) and M(2) stand for transmembrane stretches, and P for a P-loop, which folds back from the external medium into the membrane. SKT proteins distinguish themselves in two important aspects from K(+) channels: first, with just one conserved glycine residue in their P-loops they contain a much simpler K(+)-selectivity filter sequence than K(+) channels with their conserved Thr-Val-Gly-Tyr-Gly sequence. Secondly, the middle part M(2C2) from the long transmembrane stretch M(2C) of KtrB from the bacterium Vibrio alginolyticus forms a gate inside the membrane, which prevents K(+) permeation to the cytoplasm. Beside the mechanism of K(+) transport via KtrB and other SKT proteins existing hypotheses of how the KtrA protein regulates the K(+)-transport activity of KtrB are discussed.
authors.affiliation: University of Osnabrück, Faculty of Biology and Chemistry, Department of Microbiology, Osnabrück, Germany. i.haenelt@rug.nl
authors.forename: Inga
authors.initials: I
authors.lastname: Hänelt
authors.forename: Nancy
authors.initials: N
authors.lastname: Tholema
authors.forename: Nadine
authors.initials: N
authors.lastname: Kröning
authors.forename: Marc
authors.initials: M
authors.lastname: Vor der Brüggen
authors.forename: Dorith
authors.initials: D
authors.lastname: Wunnicke
authors.forename: Evert P
authors.initials: EP
authors.lastname: Bakker
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011188:Potassium / Q000378:metabolism*; D017433:Protein Structure, Secondary; D021381:Protein Transport; D044149:Vibrio alginolyticus / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; C113206:KtrB protein, Bacteria; D011188:Potassium