One of the unsolved puzzles in molecular biology is the way in which amino acid sequence codes for the native structure of proteins. Closely related to this is the question of how a protein folds into its native structure. It is believed that some crucial steps in the formation of secondary and tertiary structure of globular proteins take place on the sub-millisecond time scale, but there are as yet no general and direct experimental investigations of very early folding dynamics. The objective of our research is to develop an experimental methodology and instrumentation which can monitor the folding of the protein backbone in vitro in a single sweep from 10 nanoseconds to 1 millisecond. We use a nanosecond infrared laser-induced temperature jump to bring a cold-denatured protein such as myoglobin across the refolding phase transition, then monitor tryptophan fluorescence as well as near-and far- UV CD at 13 ns intervals using a mode-locked UV pulse train. The fluorescence or circular dichroism history is recorded in a single sweep for different tryptophan mutants of the protein, and the resulting time-resolved information correlated with static fluorescence and CD Measurements to yield a picture of folding history. Our samples have often not been fully characterized under the conditions we use, and facilities at the UIUC Fluorescence Dynamics Lab are used to provide needed thermodynamic, fluorimetric, and CD information.
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