title: Probing the structure of the mechanosensitive channel of small conductance in lipid bilayers with pulsed electron-electron double resonance.
abstract: 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.
authors.affiliation: Centre for Biomolecular Sciences, University of St. Andrews, St. Andrews, Scotland.
authors.forename: Richard
authors.initials: R
authors.lastname: Ward
authors.affiliation: Centre for Biomolecular Sciences, University of St. Andrews, St. Andrews, Scotland.
authors.forename: Christos
authors.initials: C
authors.lastname: Pliotas
authors.affiliation: Centre for Biomolecular Sciences, University of St. Andrews, St. Andrews, Scotland.
authors.forename: Emma
authors.initials: E
authors.lastname: Branigan
authors.affiliation: School of Medicine, University of St. Andrews, St. Andrews, Scotland.
authors.forename: Christian
authors.initials: C
authors.lastname: Hacker
authors.affiliation: Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland.
authors.forename: Akiko
authors.initials: A
authors.lastname: Rasmussen
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Bonn, Bonn, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Hagelueken
authors.affiliation: Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Booth
authors.affiliation: Institute of Medical Sciences, University of Aberdeen, Aberdeen, Scotland.
authors.forename: Samantha
authors.initials: S
authors.lastname: Miller
authors.affiliation: School of Medicine, University of St. Andrews, St. Andrews, Scotland.
authors.forename: John
authors.initials: J
authors.lastname: Lucocq
authors.affiliation: Centre for Biomolecular Sciences, University of St. Andrews, St. Andrews, Scotland. Electronic address: jhn@st-andrews.ac.uk.
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Bonn, Bonn, Germany; Centre for Biomolecular Sciences, University of St. Andrews, St. Andrews, Scotland. Electronic address: schiemann@pc.uni-bonn.de.
authors.forename: Olav
authors.initials: O
authors.lastname: Schiemann
mesh_terms: D000595:Amino Acid Sequence; D003461:Crystallography; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D007473:Ion Channels / Q000737:chemistry* / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; C469542:MscS protein, E coli