title: Crystal structure of a potassium ion transporter, TrkH.
abstract: The TrkH/TrkG/KtrB proteins mediate K(+) uptake in bacteria and probably evolved from simple K(+) channels by multiple gene duplications or fusions. Here we present the crystal structure of a TrkH from Vibrio parahaemolyticus. TrkH is a homodimer, and each protomer contains an ion permeation pathway. A selectivity filter, similar in architecture to those of K(+) channels but significantly shorter, is lined by backbone and side-chain oxygen atoms. Functional studies showed that TrkH is selective for permeation of K(+) and Rb(+) over smaller ions such as Na(+) or Li(+). Immediately intracellular to the selectivity filter are an intramembrane loop and an arginine residue, both highly conserved, which constrict the permeation pathway. Substituting the arginine with an alanine significantly increases the rate of K(+) flux. These results reveal the molecular basis of K(+) selectivity and suggest a novel gating mechanism for this large and important family of membrane transport proteins.
authors.affiliation: Department of Physiology & Cellular Biophysics, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, New York 10032, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Cao
authors.forename: Xiangshu
authors.initials: X
authors.lastname: Jin
authors.forename: Hua
authors.initials: H
authors.lastname: Huang
authors.forename: Mehabaw Getahun
authors.initials: MG
authors.lastname: Derebe
authors.forename: Elena J
authors.initials: EJ
authors.lastname: Levin
authors.forename: Venkataraman
authors.initials: V
authors.lastname: Kabaleeswaran
authors.forename: Yaping
authors.initials: Y
authors.lastname: Pan
authors.forename: Marco
authors.initials: M
authors.lastname: Punta
authors.forename: James
authors.initials: J
authors.lastname: Love
authors.forename: Jun
authors.initials: J
authors.lastname: Weng
authors.forename: Matthias
authors.initials: M
authors.lastname: Quick
authors.forename: Sheng
authors.initials: S
authors.lastname: Ye
authors.forename: Brian
authors.initials: B
authors.lastname: Kloss
authors.forename: Renato
authors.initials: R
authors.lastname: Bruni
authors.forename: Erik
authors.initials: E
authors.lastname: Martinez-Hackert
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Hendrickson
authors.forename: Burkhard
authors.initials: B
authors.lastname: Rost
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Javitch
authors.forename: Kanagalaghatta R
authors.initials: KR
authors.lastname: Rajashankar
authors.forename: Youxing
authors.initials: Y
authors.lastname: Jiang
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry; D015640:Ion Channel Gating; D017136:Ion Transport; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014736:Vibrio parahaemolyticus / Q000737:chemistry*
chemical_list: D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins; D015221:Potassium Channels; C443122:TrkH protein, E coli; D011188:Potassium