Engineering protein thermal stability. Sequence statistics point to residue substitutions in alpha-helices

Amino acid sequences have been compared for thermophilic and mesophilic molecules from six different protein families, which include lactate and glyceraldehyde-3-phosphate dehydrogenases, triose phosphate isomerases, superoxide dismutases, thermolysins and subtilisins. Since a three-dimensional structure was known for at least one of the sequences in each family, analysis of preferred residue substitutions, presumably to achieve thermal stability, could be examined from a structural context. The overall results, which are generally consistent across all the families, suggested decreased flexibility and increased hydrophobicity in alpha-helical regions as the main stabilizing principles. The most favoured residual exchanges, hopefully useful in engineering stability into proteins, are discussed.