Abstract
MscS (mechanosensitive channel of small conductance) is ubiquitously found among bacteria and has been proposed to play major role in the protection against rapid osmotic downshock. Although the gene has been cloned and X-ray crystallographic analysis has identified the 3D structure of the open channel, much less is known how MscS senses membrane tension. In this study, we examined the function of the mutants generated by scanning mutagenesis to identify the amino acid residues responsible for sensing membrane tension. Channel functions were examined by the patch clamp (in vitro) and hypo-osmotic shock (in vivo) methods. A hydrophilic amino acid (asparagine) replaced one of the hydrophobic residues that are thought to make contact with the lipid bilayer. Replacement of the hydrophobic residues near the periplasmic or cytoplasmic end of TM1 or TM2 transmembrane domain decreased the sensitivity of MscS to tension in the inside-out patch membrane from giant spheroplasts of E.coli. Substitution of the residues located around the center of lipid bilayer did not impair the channel's mechanosensitivity. The survival rate of bacteria challenged to hypo-osmotic shock showed comparative results with those of in vitro experiments. These findings suggest that the interaction between lipid and the both ends of TM1 and TM2 is important for tension sensing. [Jpn J Physiol 54 Suppl:S129 (2004)]
