The diverse gating mechanisms of bacterial MscS-like ion channels

Bacterial mechanosensitive (MS) channels protect cells against hypoosmotic shock by opening, in response to increased membrane tension, a transmembrane pore that allows rapid efflux of osmolytes. The MS channel of small conductance (MscS) in Escherichia coli has been extensively characterized both functionally and structurally, establishing its channel properties and revealing its architecture and the conformational changes that underlie channel gating. In particular, several lipids associated with MscS have been proposed to play a role in its mechanosensitivity. MscS is the founding member of the superfamily of MscS-like channels that share a structurally conserved core with MscS but feature additional structural elements that result in distinct functional properties. In addition to MscS, E. coli expresses five MscS-like channels. In the present review, we summarize recent advances in the structural characterization of E. coli MscS-like channels that revealed diverse gating mechanisms. Unlike the mechanosensation of MscS that appears to depend on its associated lipids, the mechanosensation of MscS-like channels seems to be the result of the deformation they cause on their surrounding membrane. Despite the diversity in observed gating mechanisms, we highlight unifying principles that dictate the properties of MscS-like channels and MS channels in general.