The docked energy was defined as the sum of the intermolecular and the internal energies. For a representative docking instance, the orientation or pose with the lowest estimated free energy (ΔG) of binding, corresponding to the docking energy and unbound free energy of the system, was chosen in each calculation. The binding free energy ratio (BFER) was defined as the ratio of the free energy binding of each enzyme–PP complex and the free energy binding of the enzyme–substrate complex.