title: Change to alanine of one out of four selectivity filter glycines in KtrB causes a two orders of magnitude decrease in the affinities for both K+ and Na+ of the Na+ dependent K+ uptake system KtrAB from Vibrio alginolyticus.
abstract: KtrAB from Vibrio alginolyticus is a recently described new type of high affinity bacterial K+ uptake system. Its activity assayed in an Escherichia coli K+ uptake negative mutant depended on Na+ ions (Km of 40 microM). Subunit KtrB contains four putative P-loops. The selectivity filter from each P-loop contains a conserved glycine residue. Residue Gly-290 from the third P-loop selectivity filter in KtrB was exchanged for Ala, Ser or Asp. KtrB variants Ser-290 and Asp-290 were without activity. In contrast, KtrB variant Ala-290 was still active. This variant transported K+ with a two orders of magnitude decrease in apparent affinity for both K+ and Na+ with little effect on Vmax.
authors.affiliation: Abteilung Mikrobiologie, Universität Osnabrück, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Tholema
authors.forename: E P
authors.initials: EP
authors.lastname: Bakker
authors.forename: A
authors.initials: A
authors.lastname: Suzuki
authors.forename: T
authors.initials: T
authors.lastname: Nakamura
mesh_terms: D000409:Alanine / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D005998:Glycine / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014733:Vibrio / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D027682:Cation Transport Proteins; C113206:KtrB protein, Bacteria; D008565:Membrane Proteins; D012964:Sodium; D000409:Alanine; D011188:Potassium; D005998:Glycine