Single amino acid substitutions producing instability of globular proteins. Calculation of their frequencies in the entire mutational spectra of the alpha- and beta-subunits of human hemoglobin.

The frequencies of substitutions resulting in protein instability were calculated by a method estimating changes in stability produced by amino acid substitutions. The method takes into account the accessibility of an amino acid position to a solvent and changes in the specificity of amino acid interactions. When tested on human mutant hemoglobins, the method yielded predictions with a preciseness of 80%. The consideration of the evolutionary homologous proteins in the analysis allowed us to estimate the evolutionary constraints imposed on stability of their spatial structure. With these limitations, approximately 50% of amino acid substitutions in the entire mutational spectra of the alpha- and beta-subunits of human hemoglobin were found to damage the spatial structure of the globular proteins.