Probing the structure of the mechanosensitive channel of small conductance in lipid bilayers with pulsed electron-electron double resonance
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Mechanosensitive channel proteins are important safety valves against osmotic shock in bacteria, and are involved in sensing touch and sound waves in higher organisms. The mechanosensitive channel of small conductance (MscS) has been extensively studied. Pulsed electron-electron double resonance (PELDOR or DEER) of detergent-solubilized protein confirms that as seen in the crystal structure, the outer ring of transmembrane helices do not pack against the pore- forming helices, creating an apparent void. The relevance of this void to the functional form of MscS in the bilayer is the subject of debate. Here, we report PELDOR measurements of MscS reconstituted into two lipid bilayer systems: nanodiscs and bicelles. The distance measurements from multiple mutants derived from the PELDOR data are consistent with the detergent-solution arrangement of the protein. We conclude, therefore, that the relative positioning of the transmembrane helices is preserved in mimics of the cell bilayer, and that the apparent voids are not an artifact of detergent solution but a property of the protein that will have to be accounted for in any molecular mechanism of gating.
Ward , R , Pliotas , C , Branigan , E , Hacker , C , Rasmussen , A , Hagelueken , G , Booth , I R , Miller , S , Lucocq , J , Naismith , J & Schiemann , O 2014 , ' Probing the structure of the mechanosensitive channel of small conductance in lipid bilayers with pulsed electron-electron double resonance ' Biophysical Journal , vol 106 , no. 4 , pp. 834-42 . DOI: 10.1016/j.bpj.2014.01.008
© 2014 The Authors. This is an Open Access article distributed under the terms of the Creative Commons-Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/2.0/), which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Funding: EaStCHEM studentship to E.B. The work was funded by BBSRC grant BB/H017917/1 to JNH, OS & IRB, The Leverhulme Foundation (EM-2012-60\2) and equipment from a Wellcome Trust Capital Award.
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