Rapid Formation of a Four-Helix Bundle. Cytochrome b_(562) Folding Triggered by Electron Transfer

Abstract

Understanding how the secondary and tertiary structures of proteins are formed from non-native conformations is a continuing challenge for both theory and experiment. This complex process involves dynamics on time scales that range from picoseconds to minutes. We have shown previously that the folding of redox-active proteins can be triggered by electron transfer (ET), thereby opening the way for investigations of early events in the folding process. Since it is important that the redox-active cofactor remains bound to the unfolded protein (eliminating the possibility that the rate-limiting step will be bimolecular capture of the cofactor), we initially thought that only redox proteins with covalently attached cofactors would be amenable to study by this method. Indeed, thus far we have restricted our work on folding dynamics to ferrocytochrome c, a protein with a covalently attached heme.