Abstract
The bacterial mechanosensitive channel MscS (mechanosensitive channel of small conductance) is known to function as a defensive device against cell rupture by hypotonic downshock. However, structure basis of its mechano-gating is little known. MscS is composed of a transmembrane (TM) part and a large cytoplasmic vestibule (CV). In this study, we investigated the role of interaction between these tow parts in MscS gating by focusing on the electrostatic interaction between charged residues in the respective parts. D62 is a negatively charged residue located in the loop connecting the TM1 and the TM2 helices and has been proposed to interact with R128 that is located at the upper surface of the CV. We examined whether D62 interacts with the CV, and if so, how the interaction contributes to MscS gating. Neutralization (D62C) or substitution (D62R) with a positively charged residue of D62 increased dramatically the threshold level for activation of MscS. In contrast, substitution with negatively charged residue (D62E) did not change the threshold. Interestingly the negative effect of D62R on mechano-activation was largely complemented by reversing the charge sign of the residue at 131 (R131D) but not with the residue at 128 (R128D), both of the residues are located in the CV being close to D62. Above findings suggest that the CV affects crucially the mechano-gating of MscS through the electrostatic interaction between D62 and R131. [J Physiol Sci. 2007;57 Suppl:S222]
