Table 1.

Calculated and experimental thermodynamics (kcal/mol) for phosphotyrosine (pY)-containing peptide analogs and their constrained counterparts binding to the SH2 domain of Grb2. fpYV(I)N is the unconstrained tri-peptide analog consisting of pY, V (or I) and N residues; cpYV(I)N are the constrained counterparts (see Figure 1). The ΔG°, ΔH° and ΔS° are the absolute binding free energy, enthalpy and entropy differences, respectively. With the calculated values of fpYVN set to experimental values, thermodynamics for the remaining ligands were computed from the relative binding free energy and enthalpy obtained from MD simulations. Statistical errors of the calculated binding free energy are given in the parenthesis.

	Calculation			Experiment14
	ΔG° (kcal/mol)	ΔH° (kcal/mol)	−TΔS (kcal/mol)	ΔG° (kcal/mol)	ΔH° (kcal/mol)	−TΔS° (kcal/mol)
fpYVN	−7.7	−5.4	−2.3	−7.7	−5.4	−2.3
cpYVN	−10.0(0.6)	−15.7	5.7(1.2)	−8.8	−7.9	−0.8
fpYIN	−7.7(0.1)	−3.2	−4.5(0.2)	−7.7	−5.5	−2.2
cpYIN	−9.8(0.4)	−14.0	4.3(0.8)	−8.6	−8.3	−0.3