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.
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.
Tholema
N
N
Abteilung Mikrobiologie, Universität Osnabrück, Germany.
Bakker
E P
EP
Suzuki
A
A
Nakamura
T
T
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*
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