An Effective Electric Dipole Model for Voltage-induced Gating Mechanism of Lysenin.

Lysenin is a pore-forming toxin, which self-inserts open channels into sphingomyelin containing membranes and is known to be voltage regulated. The mechanistic details of its voltage gating mechanism, however, remains elusive despite much recent efforts. Here, we have employed a novel combination of experimental and computational techniques to examine a model for voltage gating, that is based on the existence of an "effective electric dipole" inspired by recent reported structures of lysenin. We support this mechanism by the observations that (i) the charge-reversal and neutralization substitutions in lysenin result in changing its electrical gating properties by modifying the strength of the dipole, and (ii) an increase in the viscosity of the solvent increases the drag force and slows down the gating. In addition, our molecular dynamics (MD) simulations of membrane-embedded lysenin provide a mechanistic picture for lysenin conformational changes, which reveals, for the first time, the existence of a lipid-dependent bulge region in the pore-forming module of lysenin, which may explain the gating mechanism of lysenin at a molecular level.