Stabilization of proteins by rational design of alpha-helix stability using helix/coil transition theory

Increasing protein stability is a major goal of protein engineering because of its potential industrial and pharmacological applications. Several different rule-of-thumb strategies have been employed for such a purpose, but a general rational method is still lacking. Recently, there has been significant progress in our understanding of the interactions responsible for helix stability in monomeric peptides and this information has been included in algorithms based on the helix/coil transition theory. We set out to investigate whether it is possible to use these algorithms to rationally increase protein stability.

Using a helix/coil transition algorithm, AGADIRms, we have designed mutations affecting solvent-exposed residues which, as predicted, significantly increase the helical stability in aqueous solution of peptides corresponding to the two alpha-helices of the activation domain of procarboxipeptidase A. Introduction of the same mutations in the protein results in proteins more resistant to urea or temperature denaturation, and there is a qualitative agreement between the expected and observed increases in stability.

In this work we demonstrate that by using a helix/coil algorithm to design helix-stabilizing mutations on the solvent-exposed face of helices, it is possible to rationally increase the stability of proteins.