To compute the torsional entropies of the peptide ligands, we analyzed a minimal, non-redundant, set of rotatable torsions. Although an additional bond is present in the constrained ligands, we note that it does not introduce any new non-redundant torsions, so the constrained and flexible phosphotyrosines (cpY and fpY) were defined by the same minimal set of torsions. When computing such relative entropies comparing ligands containing glutamine versus valine, the additional glutamine-specific torsions were excluded. Analogous calculations yield the difference in entropy of torsions in the binding site residues, with ligand i versus j bound: ∆S B,ij . The rotatable torsions of the following binding site residues were analyzed: Arg13, Arg32, Ser34, Ser36, Ser42, His53, Phe54, and Lys55, which are a subset of the 13 residues used in the structural decomposition analysis (Section 3.5) that had native contacts of 4 Å or less for greater than half the simulation (see Section 3.7). In the following, we report entropies as free energy contributions of the form -T ∆S, in units of kcal/mol, to facilitate comparison with energies. The dihedral angles used for these analyses are listed in the Supporting Information. Histograms for the selected dihedrals were generated from the trajectories with cpptraj, using 180 bins of size 2 • .