Microbial K⁺ Channels

A survey of the currently available genomes shows that K⁺ channels are found in most free-living bacteria, archaea, and protists, indicating early evolution before the divergences of the three major domains of life. Though vertically descended from the primordial K⁺ channels, more recent lateral transfers of K⁺ channel genes must also have occurred. Variations in the motifs of transmembrane or cytoplasmic domains, S4 features, gating mechanism, and even the putative K⁺ filter sequence are observed. Limited experimentation and sequence survey of free-ling versus parasitic bacteria show that K⁺ channels are not essential for survival in ordinary circumstances. The lone K⁺ channel in Escherichia coli is probably not for K⁺ uptake but for resting-potential regulation in vivo. Protists (eukaryotic unicells) vary greatly; the fission yeast has no recognizable K⁺ channel gene while paramecium has 298, some three times...