Membrane Dependence of the Mechanosensitive Channel of Large Conductance

Abstract

The mechanosensitive channels of large conductance (MscL) are bacterial membrane proteins that serve as last resort emergency release valves in case of severe osmotic down shock. The channels activate with applied bilayer tension, opening a large (ca. 3 nS) mostly unselective pore. Among the mechanosensitive channels, MscL is the most studied and often used as a model for how proteins sense membrane tension. In addition to sensing bilayer tension MscL channels are influenced by various changes in the bilayer environment. For example, their gating kinetics is shifted by changes in bilayer thickness and lipid head group type; and they can be gated without applied tension by asymmetric addition of lysophosphatidylcholine.We use coarse-grained Martini molecular dynamics model[1,2] in combination with experiments to systematically explore the lipid bilayer influence on MscL function. We characterize the dependence of MscL gating kinetics on bilayer properties by simulating MscL embedded in bilayers of different composition and with systematic addition of straight chain alcohols. Both bilayer bulk properties and local properties/deformation around the proteins are analysed in addition to MscL time to opening after applied tension (ko). Analyses of over a hundred channel opening simulations reveal a short initial lag phase followed by an exponentially distributed channel opening time. In-silico predictions in different channel environments are compared with experimental data determined using reconstituted MscL in a liposomal fluorescent efflux assay. The in-silico model correctly predicts known MscL behaviour, like longer ko in thicker bilayers. Surprisingly, the model predicts longer ko with the addition of alcohols, a finding which was later experimentally confirmed. [1] S.J. Marrink, H.J. Risselada, S. Yefimov, D.P. Tieleman, A.H. De Vries. J. Phys. Chem. B 111:7812-7824, 2007. [2] S. Yefimov, E. van der Giessen, P.R. Onck, S.J. Marrink. Biophys. J., 94:2994-3002, 2008.