Mechanisms of Hydrogenase Function

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With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Brian Dyer from Emory University to investigate how living systems efficiently store energy in chemical bonds using proton coupled electron transfer processes. The most basic electron and proton transfer reactions relevant to energy storage in chemical bonds are those involved in the reduction of protons to molecular hydrogen. Man-made catalysts are not very efficient at accelerating this process, despite its relative simplicity. In contrast, living systems have evolved a class of enzymes called the hydrogenases that catalyze the reduction of protons to molecular hydrogen at extraordinary rates and with little energy loss. The hydrogenases serve as ideal models for understanding the basic principles of efficient catalysis of multi-electron, multi-proton chemistry, which is important for a wide range of applications including generation of solar fuels. While the structures of hydrogenases are well established, their mechanisms remain poorly understood; indeed, although the chemical structures of the active site of the enzymes have been exactly reproduced in synthetic mimics, these mimics fail as catalysts, highlighting the importance of the protein architecture that surrounds the active site. The Dyer group uses unique laser-based methods to elucidate the dynamics and mechanisms of the electron and proton transfer processes and the role of the protein in controlling them. This research helps students at all levels develop highly interdisciplinary skills and a knowledge base focused on renewable energy science. Training students in renewable energy science is accomplished through the Emory Chemistry Intern Program (high school students) and the Emory SURE and SIRE programs (undergraduates) with an emphasis on underrepresented minority students recruited from the Historically Black Atlanta University Center. Professor Dyer's laboratory has a strong record of dissemination of cutting edge chemical techniques such as the laser induced T-jump methods now widely used in protein folding.Hydrogenases exemplify the challenges inherent to mechanistic studies of the highly efficient oxidoreductases. These challenges are both practical, due to the difficulty of resolving the molecular processes for enzymes with kcat 1,000 s-1, and conceptual, due to the complexity of the structures and dynamics that orchestrate the electron and proton transfer reactions. Because of the extraordinarily fast catalytic rates of these enzymes, their mechanisms have been difficult to study directly. The Dyer lab recently developed an approach that enables the study of the elementary electron and proton transfer steps during fast enzyme turnover. The approach combines a laser-induced redox potential jump with time-resolved infrared spectroscopy studies of the enzyme active site. Using this unique approach, they investigate critical mechanistic questions for the hydrogenases, including how these enzymes move electrons and protons together to avoid high barrier traps (testing the principle of electroneutrality), what are the proton pathways and how are proton transfer and electron transfer gated, and what are the mechanisms of the reaction of molecular oxygen with the active site, enzyme inactivation, and reductive reactivation. Professor Dyer creates unique research opportunities to broadly train high school, undergraduate and graduate students in this research, and to help them develop highly interdisciplinary skills and gain a knowledge base focused on renewable energy science.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.