The initial geometry employed here is an equilibrated structure extracted from our previous study . First, a geometry optimization has been performed within a QM/MM framework based on the 3rd-order SCC-DFTB (DFTB3) scheme with the 3OB-f parameter set for the QM region and the AMBER03 classical force field for the MM region including the protein, lipids, solvent, and ions . We have employed the interface between DFTB+ and GROMACS to perform the QM/MM minimization using the steepest-descent algorithm.