Table I.
Parameters Characterizing the Urea Unfolding of VlsE and Hydrogen Bonding Variants in 5 mM Sodium Phosphate, pH 7.0, 25°C
| Variant | Urea 1/2a (M) | ΔUrea1/2b (M) | mc (cal mol−1 M−1) | ΔG (H2O)d (kcal mol−1) | ΔΔGe (kcal mol−1) |
|---|---|---|---|---|---|
| WT | 1.19 | – | 3860 | 4.6 | – |
| S122A | 1.02 | −0.17 | 3070 | 3.1 | −0.6 |
| S123A | 0.99 | −0.20 | 3360 | 3.3 | −0.7 |
| S213A | 1.02 | −0.17 | 3350 | 3.4 | −0.6 |
| S296A | 0.99 | −0.20 | 3770 | 3.7 | −0.7 |
| T66V | 1.25 | 0.06 | 2960 | 3.7 | 0.2 |
| T57V | 0.99 | −0.20 | 2720 | 2.7 | −0.7 |
| Y55F | 1.14 | −0.05 | 3250 | 3.7 | −0.2 |
a
Midpoint of the unfolding curve. The error is ± 2%.
b
ΔUrea1/2 = Urea1/2 (variant) − Urea1/2 (WT).
c
The slope of plots of ΔG versus [Urea]. The error is ± 10%.
d
ΔG (H2O) = the intercept of plots of ΔG versus [Urea] at 0M Urea.
e
From ΔUrea1/2 × the average m value of WT and the variants (3360 cal mol−1 M−1). The negative values indicate a decrease in stability.