TRANSIENT CIRCULAR DICHROISM STUDIES OF PROTEIN MOTIONS

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Time-resolved circular dichroism (TRCD) spectroscopy is a new experimental technique that we have developed in our laboratory for the study of protein conformational dynamics. This proposal presents continued and new studies of biochemical processes using TRCD and complementary time-resolved laser spectroscopies. During the grant period, both technical developments associated with the TRCD technique and applications of this spectroscopy to the study of conformational motions in biological molecules will be pursued. It is our goal to develop the technology for collecting transient ultraviolet circular dichroism spectra. The experimental details of our approach are outlined. The proposed improvements will enable collection of ultraviolet circular dichroism spectra between 205 nm and 250 nm, at any desired time delay between 30 picoseconds and 10 microseconds following photoexcitation. This region of the optical spectrum monitors the absorption of the protein backbone. CD spectra in the ultraviolet provide a measure of the secondary structures present in proteins in solution. Continued studies on the relaxation of heme proteins following ligand photodissociation will be conducted. The major effort during this next grant period will focus on using the UV CD technique along with a variety of laser spectroscopic probes to examine the (a) secondary structure evolution in the folding and unfolding of proteins and (b) photo-induced helix-coil transitions in small polypeptides. Protein folding is an important problem in biochemistry. The application of time resolved UV CD spectroscopy to this problem offers to produce new and exciting insights into the time scales associated with the formation of protein secondary structure. Research will also be conducted aimed at developing new photochemical methods for triggering protein unfolding and folding processes.