Mechanosensitive channels protect bacteria against lysis caused by a sudden drop in osmolarity in their surroundings. Besides the channel of large conductance (MscL) and small conductance (MscS), Escherichia coli has five additional paralogs of MscS that are functional and widespread in the bacterial kingdom. Here, we present the structure of YnaI by cryo-electron microscopy to a resolution of 13 Å. While the cytosolic vestibule is structurally similar to that in MscS, additional density is seen in the transmembrane (TM) region consistent with the presence of two additional TM helices predicted for YnaI. The location of this density suggests that the extra TM helices are tilted, which could induce local membrane curvature extending the tension-sensing paddles seen in MscS. Off-center lipid-accessible cavities are seen that resemble gaps between the sensor paddles in MscS. The conservation of the tapered shape and the cavities in YnaI suggest a mechanism similar to that of MscS.
Bibliographical noteDate of Acceptance: 02/07/2015
Open Access funded by Wellcome Trust
We thank Chris Kennaway and Veselin Kukenski for their contributions in the early stages of the project, and Ian R. Booth and Samantha Miller for helpful discussions. Electron microscopy was done in the Cryo-EM facility of the University of Edinburgh, which was funded by contributions of the Wellcome Trust equipment grant WT087658 and the Scottish University Life Science Alliance (SULSA). The Aberdeen group was supported by the Wellcome Trust grant (WT092552/A/10/Z) awarded to I.R. Booth, S. Miller, T.R., J. Naismith (St. Andrews), and S. Conway (Oxford).
- cryo-electron microscopy
- osmotic stress
- protein-lipid interaction