The role of lipids in mechanosensation

The ability of proteins to sense membrane tension is pervasive in biology. A higher resolution structure of E. coli MscS, the channel of small conductance, identifies alkyl chains inside pockets formed by the transmembrane helices (TMs). Purified MscS contains E. coli lipids and fluorescence quenching demonstrates that phospholipid acyl chains exchange between bilayer and TM pockets. Molecular dynamics and biophysical analyses show that the volume of the pockets and thus the number of lipid acyl chain within them decreases upon channel opening. Phospholipids with one acyl chain per head group (lysolipids) displace normal phospholipids (two acyl chains) from MscS pockets and trigger channel opening. We propose the extent of acyl chain interdigitation in these pockets determines the conformation of MscS. Where interdigitation is perturbed by increased membrane tension or by lysolipids, the closed state becomes unstable and the channel gates.