Neutron reflectometry reveals conformational changes in a mechanosensitive protein induced by an antimicrobial peptide in tethered lipid bilayers

MscL was expressed into vesicles using cell free protein expression. Analysing these vesicles with small angle neutron scattering, the radius of gyration of the protein was determined to be between 26-29 Å, consistent with the crystal structure of individual MscL channels. The MscL composition of the formed bilayer was 14%v/v, close to the initial composition of the vesicles, and a protein protrusion extending ca. 46 Å into the solvent was determined by PNR. Addition of 1.6 and 3.2 μM pexiganan resulted in a decrease in the protrusion of MscL (from ∼46 to ∼38 Å). To our knowledge, these findings represent the first direct experimental evidence of a structural change in the C-terminus containing protrusion of MscL, triggered by an antimicrobial peptide.