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Pivotal role of the glycine-rich TM3 helix in gating the MscS mechanosensitive channel

Nature Structural & Molecular Biology volume 12, pages 113–119 (2005)Cite this article

Abstract

The crystal structure of an open form of the Escherichia coli MscS mechanosensitive channel was recently solved. However, the conformation of the closed state and the gating transition remain uncharacterized. The pore-lining transmembrane helix contains a conserved glycine- and alanine-rich motif that forms a helix-helix interface. We show that introducing 'knobs' on the smooth glycine face by replacing glycine with alanine, and substituting conserved alanines with larger residues, increases the pressure required for gating. Creation of a glycine-glycine interface lowers activation pressure. The importance of residues Gly104, Ala106 and Gly108, which flank the hydrophobic seal, is demonstrated. A new structural model is proposed for the closed-to-open transition that involves rotation and tilt of the pore-lining helices. Introduction of glycine at Ala106 validated this model by acting as a powerful suppressor of defects seen with mutations at Gly104 and Gly108.

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Figure 1: Interaction of conserved glycine-alanine pairs in TM3 of MscS.
Figure 2: Analysis of expression of MscS channels with TM3 mutations.
Figure 3: Introduction of mutations close to the seal reduces channel conductance.
Figure 4: The introduction of serine residues alters the gating pressure.
Figure 5: Structure of the MscS channel pore in the open and the putative closed states.
Figure 6: The A106V mutant exhibits two different open states.
Figure 7: A106G is a strong suppressor of mutations at Gly104 and Gly108.

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Acknowledgements

This research was supported by The Wellcome Trust (040174) (I.R.B., S.M. and M.D.E.), by the European Union Fifth Framework Programme (W.B.) (Hypersolutes; contract no. QLK3-CT-2000-00640), by the UK Biotechnology and Biological Sciences Research Council and Unilever (S.D. and S.B.), grants GM61028 and DK60818 from the US National Institutes of Health (NIH) (P.B.), grant I-1420 of the Welch Foundation (Y.L. and P.B.) and grant F49620-01-1-0503 of the Air Force Office of Scientific Review (I.I. and P.B.), and NIH grant R01 GM063919 (J.U.B.). The authors also thank L. Moir, P. Moe and U. Schumann for their contributions to this work. We thank S. Sukharev and D. Rees for preprints.

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  1. Michelle D Edwards, Yuezhou Li and Sanguk Kim: These authors contributed equally to this work.

Authors and Affiliations

  1. School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, AB25 2ZD, UK

    Michelle D Edwards, Samantha Miller, Wendy Bartlett, Susan Black, Sally Dennison & Ian R Booth

  2. Department of Physiology, University of Texas, Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, 75390–9040, Texas, USA

    Yuezhou Li, Irene Iscla & Paul Blount

  3. UCLA-DOE Center for Genomics and Proteomics, University of California Los Angeles, 611 Charles E. Young Drive E., Los Angeles, 90095–1570, California, USA

    Sanguk Kim & James U Bowie

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Correspondence to Ian R Booth.

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Edwards, M., Li, Y., Kim, S. et al. Pivotal role of the glycine-rich TM3 helix in gating the MscS mechanosensitive channel. Nat Struct Mol Biol 12, 113–119 (2005). https://doi.org/10.1038/nsmb895

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