title: Pivotal role of the glycine-rich TM3 helix in gating the MscS mechanosensitive channel.
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.
authors.affiliation: School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, AB25 2ZD, UK.
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Edwards
authors.forename: Yuezhou
authors.initials: Y
authors.lastname: Li
authors.forename: Sanguk
authors.initials: S
authors.lastname: Kim
authors.forename: Samantha
authors.initials: S
authors.lastname: Miller
authors.forename: Wendy
authors.initials: W
authors.lastname: Bartlett
authors.forename: Susan
authors.initials: S
authors.lastname: Black
authors.forename: Sally
authors.initials: S
authors.lastname: Dennison
authors.forename: Irene
authors.initials: I
authors.lastname: Iscla
authors.forename: Paul
authors.initials: P
authors.lastname: Blount
authors.forename: James U
authors.initials: JU
authors.lastname: Bowie
authors.forename: Ian R
authors.initials: IR
authors.lastname: Booth
mesh_terms: D000409:Alanine / Q000235:genetics / Q000378:metabolism; D004594:Electrophysiology; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005998:Glycine / Q000235:genetics / Q000378:metabolism*; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D017434:Protein Structure, Tertiary
chemical_list: D029968:Escherichia coli Proteins; D007473:Ion Channels; C469542:MscS protein, E coli; D000409:Alanine; D005998:Glycine