High-Throughput Simulations Reveal Membrane-Mediated Effects of Alcohols on MscL Gating

The mechanosensitive channels of
large conductance (MscL) are bacterial
membrane proteins that serve as last resort emergency release valves
in case of severe osmotic downshock. Sensing bilayer tension, MscL
channels are sensitive to changes in the bilayer environment and are,
therefore, an ideal test case for exploring membrane protein coupling.
Here, we use high-throughput coarse-grained molecular dynamics simulations
to characterize MscL gating kinetics in different bilayer environments
under the influence of alcohols. We performed over five hundred simulations
to obtain sufficient statistics to reveal the subtle effects of changes
in the membrane environment on MscL gating. MscL opening times were
found to increase with the addition of the straight-chain alcohols
ethanol, octanol, and to some extent dodecanol but not with hexadecanol.
Increasing concentration of octanol increased the impeding effect,
but only up to 10–20 mol %. Our in silico predictions
were experimentally confirmed using reconstituted MscL in a liposomal
fluorescent efflux assay. Our combined data reveal that the effect
of alcohols on MscL gating arises not through specific binding sites
but through a combination of the alcohol-induced changes to a number
of bilayer properties and their alteration of the MscL–bilayer
interface. Our work provides a key example of how extensive molecular
simulations can be used to predict the functional modification of
membrane proteins by subtle changes in their bilayer environment.