For the ff19SB simulations, the minimization and equilibration steps were following: 1) all non-water atoms constrained, 2) heavy atoms constrained, 3) protein back bone constrained and 4) no constraints. The constraint force was 50 kcal/mol in the minimizations and 10 kcal/mol in the equilibration simulations. The minimizations 1-4 used the steepest descent algorithm with a maximum of 10,000 steps. The equilibration steps 1-3 consisted of 400 ps simulations, and step 4 was a 4,000 ps simulation. In the first equilibration step, the system was heated to 310 K. The temperature and pressure were maintained with Langevin thermostat and Berendsen barostat in the equilibration simulations. For the ff14SB, steps 2-4 were used in the minimization procedure and steps 2 and 4 for the equilibration runs of 20 ps and 2000 ps, respectively.