ANALYSIS OF PROTEIN CONFORMATIONAL CHARACTERISTICS RELATED TO THERMOSTABILITY

The thermal stability of proteins was studied, 195 single amino acid r esidue replacements reported elsewhere being analysed for several prot ein conformational characteristics: type of residue replacement; conse rvative versus nonconservative substitution; replacement being in a ho mologous stretch of amino acid residues; change in hydrogen bond, van der Waals and secondary structure propensities; solvent-accessible ver sus inaccessible replacement; type of secondary structure involved in the substitution; the physico-chemical characteristics to which the th ermostability enhancement can be attributed; and the relationship of t he replacement site to the folding intermediates of the protein, when known. From the above analyses, some general rules arise which suggest where amino acid substitutions can be made to enhance protein thermos tability: substitutions are conservative according to the Dayhoff matr ix; mainly occur on conserved stretches of residues; preferentially oc cur on solvent-accessible residues; maintain or enhance the secondary structure propensity upon substitution; contribute to neutralize the d ipole moment of the caps of helices and strands; and tend to increase the number of potential hydrogen bonding or van der Waals contacts or improve hydrophobic packing.