Potassium/proton antiport system of Escherichia coli

Abstract

The intracellular level of potassium (K+) in Escherichia coli is regulated through multiple K+ transport systems. Recent data indicate that not all K+ extrusion system(s) have been identified (15). Here we report that the E. coli Na+(Ca2+)/H + antiporter ChaA functions as a K+ extrusion system. Cells expressing ChaA mediated K+ efflux against a K+ concentration gradient. E. coli strains lacking the chaA gene were unable to extrude K+ under conditions in which wild-type cells extruded K +. The K+/H+ antiporter activity of ChaA was detected by using inverted membrane vesicles produced using a French press. Physiological growth studies indicated that E. coli uses ChaA to discard excessive K+, which is toxic for these cells. These results suggest that ChaA K+/H+ antiporter activity enables E. coli to adapt to K+ salinity stress and to maintain K+ homeostasis. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.