MD simulations were executed with OpenMM 7.1.0 33 using a Langevin integrator with a 2fs timestep and a friction coefficient of 10/picosecond. Backbone atoms were restrained with a force constant of 5 kcal/mol/Å 2 . For simulations wherein the torsional barrier was inflated (further details below), the periodic torsion force constant on the valine χ 1 dihedral was increased by 2.6X (from 3.8 to 10 kcal/mol) to mimic the barrier to rotation found for valine in the crowded environment of a binding pocket where the surroundings provide a steric barrier to rotation.