Mechanosensitive channels in archaea.

The ubiquity of mechanosensitive (MS) channels triggered a search for their functional homologues in Archaea, the third domain of the phylogenetic tree. Two types of MS channels have been identified in the cell membranes of Haloferax volcanii using the patch clamp technique. Recently MS channels were identified and cloned from two archaeal species occupying different environmental habitats. These studies demonstrate that archaeal MS channels share structural and functional homology with bacterial MS channels. The mechanical force transmitted via the lipid bilayer alone activates all to date known prokaryotic MS channels. This implies the existence of a common gating mechanism for bacterial as well as archaeal MS channels according to the bilayer model. Based on recent evidence that the bilayer model also applies to eukaryotic MS channels, mechanosensory transduction probably originated along with the appearance of the first life forms according to simple biophysical principles. In support of this hypothesis the phylogenetic analysis revealed that prokaryotic MS channels of large and small conductance originated from a common ancestral molecule resembling the bacterial MscL channel protein. Furthemore, bacterial and archaeal MS channels share common structural motifs with eukaryotic channels of diverse function indicating the importance of identified structures to the gating mechanism of this family of channels. The comparative approach used throughout this review should contribute towards understanding of the evolution and molecular basis of mechanosensory transduction in general.