Compactness of the Denatured State of a Fast-Folding Protein Measured by Submillisecond Small-Angle X-Ray Scattering

Time-resolved small-angle x-ray scattering was used to measure the radius of gyration of cytochrome c after initiation of folding by a pH jump. Submillisecond time resolution was obtained with a microfabricated diffusional mixer and synchrotron radiation. The results show that the protein first collapses to compact denatured structures before folding very fast to the native state.