Interaction of the Mechanosensitive Channel, MscS, with the Membrane Bilayer through Lipid Intercalation into Grooves and Pockets

Publication date: Available online 4 June 2019Source: Journal of Molecular BiologyAuthor(s): Tim Rasmussen, Akiko Rasmussen, Limin Yang, Corinna Kaul, Susan Black, Heloisa Galbiati, Stuart J. Conway, Samantha Miller, Paul Blount, Ian Rylance BoothAbstractAll membrane proteins have dynamic and intimate relationships with the lipids of the bilayer that may determine their activity. Mechanosensitive channels sense tension through their interaction with the lipids of the membrane. We have proposed a mechanism for the bacterial channel of small conductance, MscS, that envisages variable occupancy of pockets in the channel by lipid chains. Here, we analyse protein-lipid interactions for MscS by quenching of tryptophan fluorescence with brominated lipids. By this strategy we define the limits of the bilayer for TM1, which is the most lipid exposed helix of this protein. In addition, we show that residues deep in the pockets, created by the oligomeric assembly, interact with lipid chains. On the cytoplasmic side, lipids penetrate as far as the pore-lining helices and lipid molecules can align along TM3b perpendicular to lipids in the bilayer. Cardiolipin, free fatty acids, and branched lipids can access the pockets where the latter have a distinct effect on function. Cholesterol is excluded from the pockets. We demonstrate that introduction of hydrophilic residues into TM3b severely impairs channel function and that even ‘conservative’ hydrophobic substitutions can modulate the s...

Source: Journal of Molecular Biology - June 5, 2019 Category: Molecular Biology Source Type: research