The present calculations do replicate the experimental trend that the glutamine-containing peptides, fQ and cQ, have more favorable binding enthalpies than their valine-containing counterparts, fV and cV. Here, since the computed relative binding enthalpies are within 5.2 kcal/mol of zero, the uncertainties of up to about 2 kcal/mol in the calculations (above) are more problematic. However, the consistency of the results between both pairs of peptides supports the solidity of the result. The more favorable binding enthalpy of the glutamine-containing peptides does not correlate clearly with stronger ligand-protein interactions (∆u inter , Table ), although this might have been expected given the ability of the Q residue to hydrogen-bond with the protein. This absence of hydrogen bonds between the ligand glutamines and the protein is consistent the crystal structures. Instead, the binding site itself adopts somewhat lower energy conformations in the presence of the fQ and cQ, versus fV and cV, as evident from the positive values of ∆u B in Table .