Association between thermodynamic and evolutionary stability. Residues are classified into four (equally-spaced) categories according to their conservation entropy in Gα-MSA (1 to 4 correspond to weakest to strongest conservation), and plotted against average residue-specific stability constants in the categories. Stability constants are calculated in GDP- or GTPγS-bound forms of Gαi. Bars are standard deviation of means. There are approximately equal numbers of sites in each category (n ≈ 80). Note that in average, there is a remarkable positive association between conservation of the residues and their local thermodynamic stabilities (local stabilities of the GDP-bound form are slightly but systematically higher than those of the GTPγS-bound form).