Analysis of a putative voltage-gated prokaryotic potassium channel

Most of the completely sequenced prokaryotic genomes contain genes of potas sium channel homologues, but there is still not much known about the role o f these proteins in prokaryotes. Here we describe the large-scale overprodu ction and purification of a prokaryotic voltage-gated potassium channel hom ologue, Kch, from Escherichia coli. After successful overproduction of the protein, a specific increase in the,potassium permeability of the cells was found. Kch could be purified in large amounts using classical purification methods to prevent aggregation of the protein. The physiological state of the protein was revealed to be a homotetramer and the protein was shown to be localized to the cytoplasmic membrane of the cells. In the course of the localization studies, we found a specific increase in the density of the c ytoplasmic membrane on Kch production. This was linked to the observed incr ease in the protein to lipid ratio in the membranes. Another observed chang e in the membrane composition was an increase in the cardiolipin to phospha tidylglycerol ratio, which may indicate a specific cardiolipin requirement of Kch. On the basis of some of our results, we discuss a function for Kch in the maintenance of the membrane potential in E. coli.