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Lipid-Protein Interaction of the MscS Mechanosensitive Channel Examined by Scanning Mutagenesis

Takeshi Nomura ^*, Masahiro Sokabe ^*   and Kenjiro Yoshimura ^*  ¶

^* ICORP/SORST, Cell Mechanosensing, Japan Science and Technology Agency, Nagoya, Japan; Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya, Japan; Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan; and ^¶ Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Okazaki, Aichi, Japan

Correspondence: Address reprint requests to Kenjiro Yoshimura, Structural Biosciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan. Tel.: 81-29-853-6658; Fax: 81-29-853-6614; E-Mail: kenjiro{at}biol.tsukuba.ac.jp.

The mechanosensitive channel of small conductance (MscS) is a bacterial mechanosensitive channel that opens in response to rapid hypoosmotic stress. Since MscS can be opened solely by membrane stretch without help from any accessory protein, the lipid-protein interface must play a crucial role in sensing membrane tension. In this study, the hydrophobic residues in the lipid-protein interface were substituted one by one with a hydrophilic amino acid, asparagine, to modify the interaction between the protein and the lipid. Function of the mutant MscSs was examined by patch-clamp and hypoosmotic shock experiments. An increase in the gating threshold and a decrease in the viability on hypoosmotic shock were observed when the hydrophobic residues near either end of the first or the second transmembrane helix (TM1 or TM2) were replaced with asparagine. This observation indicates that the lipid-protein interaction at the ends of both helices (TM1 and TM2) is essential to MscS function.

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