Nanosecond time-resolved polarization spectroscopy applied to protein folding

The dynamic response of a protein to photoinitiation of folding can reveal new information about the early stages of secondary and tertiary structure formation, information beyond that obtainable from X-ray crystallography, NMR, and other steady state methods. The combined efforts of time-resolved studies using different experimental probes have already observed several events in the early stages of protein and peptide folding. However, in terms of the 'big folding picture', our understanding of protein folding is limited. Information on the folding mechanisms for a range of peptides and proteins is important to address the commonality of folding intermediates and pathways, but it is also useful to thoroughly understand the process of folding in at least one protein. To obtain such an understanding of one protein it is useful to employ a number of spectroscopic approaches. We present here the results of time-resolved absorption, CD and MCD studies of the folding reactions of reduced cytochrome c after ligand photolysis of the CO adduct. We also discuss our results and the results of other studies on cytochrome c to demonstrate the advantage of using a number of different approaches for understanding protein folding.