Potassium ion channels: could they have evolved from viruses?

All potassium channels share a common architecture consisting of their pore module with two transmembrane domains and a conserved filter region that selects for K ions. The current view is that the plethora of complex K channels in eukaryotes evolved from a pore module precursor via gene fusions and gene duplications. Here we suggest that this pore precursor might have originated from viruses. This view is fostered by new ideas and insights into the role of viruses in evolution and by the discovery of viral K channels that were not acquired from their current algal hosts. These small virus encoded channel proteins resemble the postulated pore precursor. Furthermore, the structural and functional features of complex eukaryotic K channels can be formed by a few simple genetic manipulations. Introduction Cells communicate among themselves by electrical activity. Sophisticated membrane-embedded proteins, called ion channels, catalyze rapid, selective and regulated ion fluxes across membranes (Hille, 2001). The resulting membrane currents are responsible for neuronal activity and the systemic propagation of electrical signals in animals. The activity of some channels is important for muscle movement in animals or growth in plants; other channels sense the concentration of physiological signals and modulate key processes in all kinds of eukaryotic cells. Among the many diverse ion channels in higher organisms, K channels are among the most important. One feature of K channels is that they conduct K ions much better than slightly smaller Na ions (Hille, 2001). The selective transport of K is involved in many physiological functions including homeostasis of the membrane potential and the re-polarization of the action potential in excitable cells. Because of a universal requirement for selective K fluxes across membranes, K channels are present in plasma membranes of all cell types in animals and plants. K channels also exist in organellar membranes including mitochondria, chloroplasts and endoplasmic reticulum (ER). The evolution of K channels has been traced back to the prokaryotic world where K channel proteins are common in eubacteria and archea (Jan and Jan, 1992; Anderson and Greenberg, 2001; Derst and Karschin, 1998, Martinac et al. 2006). Phylogenetic studies and structure/function properties of channel proteins have led www.plantphysiol.org on January 30, 2018 Published by Downloaded from Copyright © 2013 American Society of Plant Biologists. All rights reserved.