Force Transduction and Lipid Binding in MscL: A Continuum-Molecular Approach
We apply balanced radial pulling forces of different magnitudes and polar angles on the unbound tails of all ten tightly-bound lipids simultaneously as illustrated in (A). In these simulations there are no forces or restraints acting directly on the protein. The diagram in (B) shows regions in the lateral/normal force space for which the channel pore continuously opens under symmetric pulling (all lipids bound, green area), and where the pore opens after one or more lipids unbind and the pulling becomes asymmetric (pink area). Lower forces can readily open the pore, without subunit dissociation, when the lateral and vertical components are close in magnitude. Large forces can result in open conformations with large deformations and partial unfolding/dissociation of the protein subunits in most directions tested. (C) Vertical cross section of a surface representation of the MscL channel opened by a pulling force of 300 pN at an angle of 45°. The C-terminal bundle in this open structure remains associated in good agreement with recent experimental observations , .