Ion Channels in Microbes

Abstract

Summary Studies of ion channels have for long been dominated by the animalcentric, if not anthropocentric view of physiology. The structures and activities of ion channels had, however, evolved long before the appearance of complex multicellular organisms on Earth. The diversity of ion channels existing in cellular membranes of prokaryotes is a good example. Though at first it may appear as a paradox that most of what we know about the structure of eukaryotic ion channels is based on the structure of bacterial channels, this should not be surprising given the evolutionary relatedness of all living organisms and suitability of microbial cells for structural studies of biological macromolecules in a laboratory environment. Genome sequences of the human as well as various microbial, plant and animal organisms unambiguously established the evolutionary links, whereas crystallographic studies of the structures of major types of ion channels published over the last decade clearly demonstrated the advantage of using microbes as experimental organisms. The purpose of this review is not only to provide an account of acquired knowledge on microbial ion channels but also to show that the study of microbes and their ion channels may also hold a key to solving unresolved molecular mysteries in the future.

Structure and molecular mechanism of an anion-selective mechanosensitive channel of small conductance

“…M echanosensitive (MS) channels are the most ancient and universal membrane pores and are found in all eukaryotic and prokaryotic cells (1)(2)(3). In response to mechanical forces, MS channels open, facilitating the passive flow of particles from higher to lower concentrations (3,4).…”

Potassium Ion Channels: Could They Have Evolved from Viruses?

“…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;Derst and Karschin, 1998;Anderson and Greenberg, 2001;Martinac et al, 2008). Phylogenetic studies and structure/function properties of channel proteins have led to the hypothesis that the complex K + channels in animals and plants evolved from a simple bacterial precursor channel (Anderson and Greenberg, 2001).…”

Bacterial Mechanosensitive Channels: Models for Studying Mechanosensory Transduction

“…The criterion for the ''bilayer mechanism'' is demonstration that the purified MS channel protein remains MS when reconstituted into lipid bilayers (57). In practical terms, this means that the sensitivity of the channel to lipid bilayer tension can be demonstrated on reconstitution into liposomes (99). Bacterial and archaeal MS channels provide a clear demonstration that prokaryotic MS channels can sense membrane tension directly.…”

“…Development of the ''giant spheroplast'' preparation from E. coli cells (Fig. 5A) allowed for the first time electro-physiological studies in bacterial cell membranes (95,132) and, thus, opened the way for pioneering structure and function studies of ion channel proteins in prokaryotic microbes (99). For MS channel recording from giant spheroplast preparations, cell cultures of E. coli are grown in Luria-Bertani medium in the presence of cephalexin, which causes the cells to grow into filaments reaching a length of 50 to 150 lm.…”

“…EPR spectroscopy combined with patch-clamp recordings from both MscL and MscS channels has helped elucidate how the basic physical properties of the lipid bilayer, such as thickness, curvature, and/or pressure profile, affect conformational changes within the channel that accompany channel gating (32,99,120,127).…”