Time resolved collapse of a folding protein observed with small angle x-ray scattering

High-intensity, "pink" beam from an undulator was used in conjunction with microfabricated rapid-fluid mixing devices to monitor the early events in p rotein folding with time resolved small angle x-ray scattering. This Letter describes recent work on the protein bovine P-lactoglobulin where collapse from an expanded to a compact set of states was directly observed on the m illisecond time scale. The role of chain collapse, one of the initial stage s of protein folding, is not currently understood. The characterization of transient, compact states is vital in assessing the validity of theories an d models of the Folding process.