Biological Activation of Small Molecules: Nitrogenases and Related Biomimetic Models

Montana State University, Bozeman MT

Investigators

Abstract

Biological nitrogen fixation provides about half of the metabolically accessible nitrogen in nature, which is a fundamental basis of life on earth. This is carried out at ambient conditions from abundant atmospheric dinitrogen by a fascinating metalloenzymatic machinery. This project aims to address some of the fundamental questions about the structure and molecular mechanism of this machinery that remain unanswered despite decades of past research. The approach has the potential to contribute significantly to the design of functionally analogous biomimetic systems for agricultural and chemical technological use. A set of physical-chemical parameters will be established that is required for the activation and reduction of the N-N triple bond in dinitrogen at iron-sulfur cluster-based compounds. The chemical composition of the unknown interstititial ligand at the active site cofactor center of the Mo-containing nitrogenase metalloenzyme will be determined. Building on the above two tasks, an in silico, virtual chemical model of the metalloenzyme active site will be created, which is a long needed tool for probing the intimate molecular details of substrate binding, proton, and electron-transfer, substrate activation and transformation, and product release processes. These will be achieved by employing an innovative combination of the multi-edge X-ray absorption spectroscopic technique and a range of computational methods. Due to the complex nature of the above tasks, the research will be carried out in a multidisciplinary environment involving biochemists and enzymologists, spectroscopists, inorganic and computational chemists that will provide a unique environment for scientific discovery and student training at undergraduate, graduate, and postdoctoral levels. Broader Impact: The main scientific achievement of the project will be the specific understanding of how ligand/protein environment and cluster composition can influence the structure and reactivity of heterometal substituted iron-sulfur clusters with relevance to nitrogen fixation. This knowledge will be incorporated into a computational model of the nitrogenase active site that looks and acts in silico like the real metalloenzyme in vitro. The methodology developed is likely to impact research efforts toward the catalytic mechanism of other iron-sulfur containing metalloenzymes. As part of student training, the principal investigator's students will learn the fine details of metalloenzymatic and biomimetic sample preparations from collaborators. Conversely, the principal investigator will train the collaborators' students in synchrotron science, physical inorganic chemistry, and computational chemistry. The research activities and scientific insights will be disseminated via peer-reviewed journals, conferences and meetings, and electronically via the research group's website.