Pivotal role of the glycine-rich TM3 helix in gating the MscS mechanosensitive channel.
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.
Edwards
Michelle D
MD
School of Medical Sciences, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, AB25 2ZD, UK.
Li
Yuezhou
Y
Kim
Sanguk
S
Miller
Samantha
S
Bartlett
Wendy
W
Black
Susan
S
Dennison
Sally
S
Iscla
Irene
I
Blount
Paul
P
Bowie
James U
JU
Booth
Ian R
IR
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
D029968:Escherichia coli Proteins; D007473:Ion Channels; C469542:MscS protein, E coli; D000409:Alanine; D005998:Glycine