NSF/BIO-DFG: Biological Fe-S intermediates in the synthesis of nitrogenase metalloclusters

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Nitrogen gas (N2) is the most abundant source of nitrogen on Earth. However, this nutrient source is only biologically accessible to a subset of microbes that can reduce it into ammonium NH4+. The biological capacity to fix N2 is a critical step in the biogeochemical nitrogen cycle and essential to life on Earth. The enzyme responsible for this reaction is nitrogenase and its activity relies on its associated metallocofactors. This project aims to elucidate initial reaction steps involving the synthesis of nitrogenase metallocofactors that are promoted by proteins NifU and NifS. Previous studies have established the involvement of these proteins in supporting the synthesis of initial iron-sulfur (Fe-S) building blocks for nitrogenase metallocofactors. The research supported by this award will explore how NifU and NifS assemble these Fe-S units in the model bacterium Azotobacter vinelandii. The interdisciplinary, collaborative international project will engage undergraduate and graduate students through research experiences and professional development opportunities. A German and an American PI partnership will support two synergistic research and professional development efforts: (a) collaborative research experiences abroad for graduate students and (b) mentored research fellowships for local undergraduate students. These efforts are relevant for preparing the next generation of STEM leaders for a diverse and globalized workforce. The project is aimed at investigating the mechanistic and chemical steps of Fe-S cluster synthesis in the context of a native environment and the presence of physiological reductants by establishing 1) the location and spectroscopic features of novel cluster species associated with NifU, 2) the involvement additional factors in this process, and 3) the reactivity of newly identified cluster species as building blocks for the synthesis of nitrogenase metalloclusters. Uncovering molecular and mechanistic details that enable nitrogen fixation has intrinsic intellectual merit in understanding their sustained and conserved requirement throughout evolution. These principles can also guide foundational studies on Fe-S clusters on more complex systems that utilize metallocofactors participating in other cellular processes. This collaborative US/Germany project is supported by the US National Science Foundation (Chemistry and Molecular and Cellular Biosciences Divisions jointly) and the German Research Foundation (DFG).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.