Intramolecular Vibrational Excitation of Protein Unfolding and Refolding Dynamics

点击翻译按钮获取中文摘要

This project employs time-resolved fluorescence spectroscopy to study how small proteins change in structure when they are displaced from the equilibrium or native structure. The planned research exploits a new method developed in this laboratory that uses the vibrational energy transferred from an excited-state electronic chromophore to drive the host protein to which it is attached from its native structure to a range of partially unfolded states that probably correspond to late intermediates along the folding/unfolding pathway. Because the intermediate structures are generated optically under the solution conditions that favor the native structure, the refolding reactions that follow the production of unfolded intermediates can be characterized with independent control of the solvent composition or temperature over a very wide range of timescales, over the picosecond to millisecond regime, through the use of prompt and delayed fluorescence methods. Zinc(II)-substituted and metal-free cytochromes c are the main systems to be studied. The porphyrin chromophore in cytochrome c serves in the planned experiments as both the trigger and the sensor for the unfolding and refolding reactions. A tryptophan residue will also be used as a remote sensor for the reactions that are triggered by the porphyrin. This research provides a direct test of the central hypothesis that proteins fold rapidly under physiological conditions because they move randomly on a funnel-shaped potential-energy surface that has the native structure at the funnel's minimum. The research will also have an impact on the broader fields of protein structure and function that relate to the barrier-crossing processes that lead to conformational changes during photobiological and enzyme-catalyzed reactions.This project plays an integral part in the teaching of undergraduate and graduate courses by the PI and co-PI. It provides key lecture topics and applications even in introductory courses. Research participants are exposed to a wide range of disciplines ranging from structural biology to chemical physics. Undergraduate students are encouraged to start working in the laboratory in the freshman year, and they usually contribute to publications by the senior year. Additionally, this project is associated with a new outreach program that will feature visits by the PI and co-PI to high schools in the Lansing, Michigan area to give presentations to Chemistry and Physics classes on the use of laser spectroscopy in biophysical chemistry, structural biology, and related disciplines. Interested students and their teachers will then be invited to visit the PI, co-PI, and their graduate students, to see the research laboratories, to talk about careers in science and engineering, and perhaps to get involved in research projects. This outreach plan will lead to interactions with students from underrepresented groups who will be recruited to undertake undergraduate studies in the sciences at Michigan State University. This effort is intended to augment an existing effort by the Department of Chemistry at MSU to recruit and retain students from underrepresented groups.