title: The Structure of YnaI Implies Structural and Mechanistic Conservation in the MscS Family of Mechanosensitive Channels.
abstract: 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.
authors.affiliation: Institute of Structural and Molecular Biology, School of Biological Sciences, University of Edinburgh, Michael Swann Building, Max Born Crescent, Edinburgh EH9 3BF, UK. Electronic address: bettina.boettcher@ed.ac.uk.
authors.forename: Bettina
authors.initials: B
authors.lastname: Böttcher
authors.affiliation: Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors.forename: Vojtech
authors.initials: V
authors.lastname: Prazak
authors.affiliation: Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors.forename: Akiko
authors.initials: A
authors.lastname: Rasmussen
authors.affiliation: Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Black
authors.affiliation: Institute of Medical Sciences, School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK. Electronic address: t.rasmussen@abdn.ac.uk.
authors.forename: Tim
authors.initials: T
authors.lastname: Rasmussen
mesh_terms: D020285:Cryoelectron Microscopy; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D007473:Ion Channels / Q000737:chemistry* / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D014364:Tryptophan / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; D008563:Membrane Lipids; C469542:MscS protein, E coli; C580573:YnaI protein, E coli; D014364:Tryptophan
keywords: bacteria; cryo-electron microscopy; fluorescence; osmotic stress; protein-lipid interaction