Structure and Dynamics of CO Binding to Nitrogenase via Ultrafast Vibrational Spectroscopy

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Nitrogenases are important enzymes that catalyze the conversion of nitrogen to ammonia and play key roles in the global nitrogen cycle. Recently, they have also been shown to convert carbon monoxide (CO) to hydrocarbons and, therefore, are recognized as important candidates for the production of biofuels. With this award, the Chemistry of Life Processes Program in the Division of Chemistry at NSF is funding Professor Nien-Hui Ge from the University of California, Irvine, to investigate how CO binds to and interacts with nitrogenases. Although nitrogenases have been well studied, the detailed mechanisms for CO binding and reactions are still lacking. This project will apply state-of-the-art ultrafast vibrational spectroscopy to capture molecular motions using laser pulses at "shutter speeds" faster than one-trillionth of a second. These snap-shots provide new and much needed information on the molecular structure and transient dynamics of CO and nitrogenases as they bind and interact with each other. Graduate students participating in the research gain valuable training with advanced laser techniques and core physical sciences to strengthen their career development. This project is also integrated with outreach efforts that engage K-12 students through scientific demonstrations. This project is undertaken to gain a molecular picture of CO binding to molybdenum- and vanadium-dependent nitrogenases by novel applications of ultrafast two-dimensional infrared spectroscopy and a variety of transient measurements. The high time resolution of these techniques allows the study of rapid structural fluctuations and transitions of the enzyme. When combined with computational modeling, these experiments reveal the structure of CO at binding sites, elucidate local environment around the cofactor, and establish connectivities between different CO species. Detailed structural and dynamic information obtained from this project provides new insight and helps to establish a unified mechanism for CO binding to nitrogenases.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.