Umbrella samping was executed in OpenMM 7.1.0 33 using a Langevin integrator with a 1fs timestep and a friction coefficient of 10/picosecond. The dipeptide backbone atoms were restrained with a force constant of 5 kcal/mol/Å 2 . The atoms forming the dihedral angle of the valine χ 1 were harmonically restrained with a force constant of 200 kcal/mol/Å 2 for 36 10 • χ 1 simulation windows (0 • -350 • ). The simulation for each window was run for 3,000,000 steps (3 ns).