Electrostatics at the membrane define MscL channel mechanosensitivity and kinetics

Area of Science:

• Biophysics
• Molecular Biology
• Structural Biology

Background:

• Bacterial mechanosensitive channel of large conductance (MscL) acts as a cellular emergency release valve against osmotic stress.
• MscL is a model protein for understanding how proteins sense membrane tension.
• The role of electrostatic interactions in MscL gating, beyond hydrophobicity, remains largely unexplored.

Purpose of the Study:

• To investigate the contribution of electrostatic interactions to the gating mechanism of MscL.
• To differentiate between protein-protein and protein-lipid electrostatic contributions to MscL function.

Main Methods:

• Construction and analysis of MscL chimeras from distinct bacterial orthologues (E. coli and S. aureus).
• Site-directed mutagenesis to alter specific residues, including K101 in E. coli MscL.
• Reconstitution of MscL variants into liposomes with varying lipid head groups to assess protein-lipid interactions.

Main Results:

• Mutation of a single residue (K101) in E. coli MscL to a negatively charged residue altered channel gating, reducing mechanosensitivity and increasing open dwell times.
• Both protein-protein and protein-lipid electrostatic interactions were found to influence MscL gating.
• Protein-lipid electrostatic interactions were identified as the primary determinant of the observed channel phenotype.

Conclusions:

• Electrostatic interactions, especially with the lipid bilayer, play a crucial role in modulating MscL channel gating dynamics.
• The findings propose a model where protein-lipid electrostatics are key to MscL's response to membrane tension.
• This study expands the understanding of MscL mechanosensation beyond hydrophobic effects.