Here 𝐸 "⃗ ()*+,$-and 𝐸 "⃗ ,/01%2 refer to the electric field at a given site in the fully solvated protein-ligand complex, and in a ligand-only system stripped of receptor and solvent, respectively. Fields were first calculated at the two atoms of the isomerized peptide bond -the proline N atom and the carbonyl C atom of the preceding residue (Fig. ). Atom-centered fields were then linearly interpolated to provide the field experienced at the bond midpoint. After AMOEBA simulations, the electric fields 𝐸 "⃗ ()*+,$-at the C and N atoms were calculated directly for each trajectory frame using the instantaneous induced atomic dipole at each atomic site, 𝜇 ⃗ /%2 , and the relevant atomic polarizability taken from the AMOEBA force field, 𝛼: