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

• Published in: Journal of molecular biology 2019-08, Vol.431 (17), p.3339-3352
• Main Authors: Rasmussen, Tim, Rasmussen, Akiko, Yang, Limin, Kaul, Corinna, Black, Susan, Galbiati, Heloisa, Conway, Stuart J., Miller, Samantha, Blount, Paul, Booth, Ian Rylance
• Format: Article
• Language: English
• Subjects: Biochemical Phenomena; Biological Transport; brominated lipids; Cardiolipins; electrophysiology; Escherichia coli - metabolism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; fluorescence quenching; Hydrophobic and Hydrophilic Interactions; Ion Channels - chemistry; Ion Channels - genetics; Ion Channels - metabolism; Lipid Bilayers - chemistry; Lipid Bilayers - metabolism; lipid–protein interaction; Models, Molecular; Phospholipids - chemistry; Protein Binding; Protein Conformation; Protein Interaction Domains and Motifs; tension sensing; Tryptophan - metabolism
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2019.05.043

All 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 analyze 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 stability of the open pore. The data provide important insights into the interactions between phospholipids and MscS and are discussed in the light of recent developments in the study of Piezo1 and TrpV4. [Display omitted] •MscS tension-sensing relies on dynamic molecular interactions with lipids.•Branched lipids or protein mutations that change these interactions modify gating.•Lipids can penetrate in pockets deep within MscS by changing orientation.•Tryptophan fluorescence quenching is defined by bilayer lipid interactions with MscS.•MscS deforms the shape of the membrane in a manner similar to Piezo1.