Mechanosensitive Channels in Prokaryotes

Compared to voltage-dependent or ligand-gated ion channels that have extensively been studied over the last twenty years, there is little knowledge available on structure and function of mechanosensitive (MS) channels that constitute the third major group of ion channels classified according to their gating mechanism. The main purpose of this review is to summarize an area of the MS channel research where major progress has occurred. Cloning of MscL and MscS, the MS channels of Large and Small conductance found in Bacteria and elucidation of the 3D crystal structure of MscL are discussed in conjunction with the physiological role of the MS channels in bacterial osmoregulation. Furthermore, cloning and molecular characterization of MS channels in Archaea Methanococcus jannashii and Thermoplasma acidophilum are described. They present examples of the recent promising developments, which may ultimately lead to the understanding of the biophysical principles and evolutionary origins of mechanosensory transduction. Although they conduct ions and are usually characterized by their ionic conductance and selectivity, the MS channels in prokaryotes may primarily serve to transport osmoticants other than ions. Therefore, throughout this review prokaryotic MS ion channels are referred to as MS channels rather than MS ion channels.