Substitutions of Amino Acids with Large Number of Contacts in the Native State Have no Effect on the Rates of Protein Folding

•A rule is proposed on the effects of mutations of highly connected residues•Mutations of highly connected hydrophobic residues should affect unfolding rates•Such mutations would not change the folding rates of a protein•Experimental support of this hypothesis is provided•This rule can facilitate the work on constructing mutant forms of proteins

Various effects of amino acid substitutions on properties of globular proteins have been described in a large number of research papers. Nevertheless, no definite “rule” has been formulated as of yet that could be used by experimentalists to introduce desirable changes in the properties of proteins. Herein we attempt to establish such a “rule”. To this end, a hypothesis is proposed on the effects of substitutions of hydrophobic residues with large number of contacts on free energies of different states of a globular protein. The hypothesis states: Substitutions of hydrophobic residues engaged in a large number of residue-residue contacts would not change the folding rate of a protein but could affect its unfolding rate. This hypothesis was verified by both theoretical and experimental analyses, generating a general rule that can facilitate the work of experimentalists on constructing mutant forms of proteins.