Biophysical Studies of Metalloenzymes

Northwestern University, Evanston IL

Investigators

Abstract

Title: Biophysical Studies of Metalloenzymes This project is jointly funded by the Molecular Biophysics Cluster in the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences Systems Program and the Chemistry of Life Processes Program in the Division of Chemistry in the Directorate of Mathematical and Physical Sciences. Bioavailable nitrogen derived from ammonia produced by the reduction of atmospheric nitrogen is second only to water as the limiting nutrient in plant growth. From the appearance of the enzyme nitrogenase approximately two billion years ago, until the wide-spread use of the Haber-Bosch process in the 1950's for the chemical production of ammonia fertilizers, all life obtained nitrogen from biological nitrogen fixation using the nitrogenase enzyme. Currently, biological nitrogen fixation using nitrogenase supplies approximately one-half of the world's ammonia. The remaining half is produced by the Haber-Bosch industrial process, a process that is responsible for approximately 2% of the world's total energy consumption. The goal of this research is to reveal the mechanism of nitrogenase function. Understanding of nitrogenase function will potentially enable the effective utilization of nitrogenase activity for greater human benefit, increasing food production and reducing energy consumption during the industrial production of ammonia fertilizers. In addition, investigators are active in science education and training at all levels. The first goal of this project is to further refine the nitrogenase reaction mechanism elucidated by the investigators through the use of genetic/biochemical approaches for the isolation of catalytic intermediates in combination with the laboratory's use of electron-nuclear double resonance (ENDOR) and electron spin-echo envelope modulation (ESEEM) spectroscopies to characterize the reaction intermediates. A second goal of the project is to determine the structure and electronic properties of enzymatic intermediates throughout the catalytic cycle, by integrating hydrogen, deuterium, (14,15)nitrogen, (57)Fe and (95)Mo ENDOR/ESEEM spectroscopic studies with quantum chemical calculations that for the first time introduce QM/MM methods to the study of nitrogenase intermediates. The third goal of the project is to study the biomimetic molybdenum and iron complexes in order to advance the understanding of the biocatalytic potential of these complexes. EPR/ENDOR characterizations of biomimetic Mo and Fe complexes yield powerful constraints on the identification of substrate-derived moieties in our nitrogenase intermediates. In addition, these complexes have their own, fundamental importance to coordination chemistry that include non-classical M-H(2) adducts that show novel H(2) rotational dynamics and also are relevant for hydrogen catalysis and energy storage.