  For ion channel gating, the appearance of two distinct conformational states
and the discrete transitions between them is essential, and therefore of
crucial importance to all living organisms. We show that the physical interplay
between two structural elements that are commonly present in bacterial
mechanosensitive channels, namely a charged vestibule and a hydrophobic
constriction, creates two distinct conformational states, open and closed, as
well as the gating between them. We solve the nonequilibrium
Stokes-Poisson-Nernst-Planck equations, extended to include a molecular
potential of mean force, and show that a first order transition between the
closed and open states arises naturally from the diffusio-osmotic stress caused
by the ions and water inside the channel and the elastic restoring force from
the membrane. Our proposed gating mechanism is likely to be important for a
broad range of ion channels, as well as for biomimetic channels and ion
channel-targeting therapeutics.
