Molecular Chaperones as Buffers for Functionality during Protein Evolution

It is well known that molecular chaperones, or heat shock proteins, play an important role in ensuring the proper folding of newly synthesized proteins in vivo. However, less understood is the role that these proteins may play in the context of evolution, enabling a broader phenotypic sampling of sequence space. We hypothesize that by buffering the tolerance of proteins to destabilizing mutations, chaperones give these proteins an increased range of improved functional mutations to try. By generating mutant libraries of the proteins cytochrome P450 BM3 and chloramphenicol acetyltransferase and screening them in various chaperone-impaired strains of E. Coli, we have found and characterized a number of mutants that depend on chaperones to fold and function properly. These results imply that chaperones are part of natural mechanism for protein evolution and illuminate a potential application for accelerated directed evolution.