Table 1.

Thermodynamic parameters for the unfolding of α₂D and variants^*

Glu7 variant	ΔΔG₂₉₈^† (kcal mol⁻¹) (1 M)	ΔG₂₉₈^† (kcal mol⁻¹) (1 M)	T_m^‡ (°C) (100 μM)	T_m^‡ (K) (1 M)	ΔH_m^§ (kcal mol⁻¹) (100 μM)	ΔH_m^§ (kcal mol⁻¹) (1 M)	ΔC_p (cal mol⁻¹ K⁻¹)
E	-	7.0	51.8	369.8	30.7	69.3	860
A	0.2	7.2	53.2	370.1	32.6	70.2	860
S	−0.8	6.2	37.7	358.5	23.4	64.3	860
D	−1.4	5.6	27.3	354.4	14.2	60.6	860
H	−1.1	5.9	36.0	363.1	16.2	62.5	860
Y	1.0	8.0	65.0	379.7	39.4	75.1	860
F	0.5	7.5	72.7	404.2	28.5	61.0	558
V	−0.4	6.6	50.1	405.1	7.6	55.5	514

Thermal denaturation data of peptide samples (pH 7.3, 50 mM Na₂HPO₄) were obtained by monitoring ellipticity at 222 nm. Multiple datasets at various peptide concentrations were globally analyzed using the Gibbs-Helmholtz equation using a 100 μM (or 1 M) standard state as described [60]. The computed values of ΔC_p were constant given the precision of these parameters (± 10% based on sensitivity analysis). Therefore, a single value of ΔC_p was used for all samples (860 ± 100 cal mol⁻¹ K⁻¹ dimer–1) except E7F and E7V (see the Discussion section).

^†

ΔG₂₉₈ is the Gibbs free energy for the folding–unfolding transition at 25°C, 1 M standard state; units are kcal mol⁻¹.

^‡

T_m is the midpoint of the folding–unfolding transition (at the standard state indicated) and is precise to 0.4°C.

^§

The ΔH_m is the extrapolated enthalpy for the folding–unfolding transition at T_m (at the standard state indicated); units are kcal mol⁻¹ and the uncertainty is ± 0.8 kcal mol⁻¹.