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

FEBS Lett. 1999 May 7;450(3):217-20. doi: 10.1016/s0014-5793(99)00504-9.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / genetics
  • Alanine / metabolism*
  • Amino Acid Sequence
  • Amino Acid Substitution
  • Bacterial Proteins*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cation Transport Proteins*
  • Glycine / genetics
  • Glycine / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Mutagenesis
  • Potassium / metabolism*
  • Sodium / metabolism*
  • Vibrio / metabolism*


  • Bacterial Proteins
  • Carrier Proteins
  • Cation Transport Proteins
  • KtrB protein, Bacteria
  • Membrane Proteins
  • Sodium
  • Alanine
  • Potassium
  • Glycine