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Published July 2017 | public
Journal Article

Site-specific X-ray Absorption Spectroscopy Study on Nitrogenase MoFe-protein

Abstract

Nitrogenase is the only known biochemical machinery responsible for biological nitrogen fixation. In the process of biological nitrogen fixation, the nitrogenase MoFe-protein catalyzes the reduction of dinitrogen to ammonia at the FeMo-cofactor, upon receiving the electrons from the donor via Fe-protein. The two unusually large metalloclusters, the [7Fe:9S:Mo:C] FeMo–cofactor and [8Fe:7S] P–cluster, in the MoFe-protein highlight the richness of the redox chemistry available to nitrogenase for dinitrogen reduction. The information on the site-specific charge distribution within these metalloclusters is crucial towards ultimately understanding the mechanisms of nitrogenase at atomic-level. Multi-wavelength X-ray anomalous diffraction (MAD), by combining the strength of X-ray diffraction and X-ray absorption spectroscopy (XAS), provides a powerful tool for probing the local structure of the metals in a site-specific fashion. We have applied site-specific XAS to the MoFe-protein and other Fe-Sproteins as models for the study. The acquired site-specific Fe K-edge absorption spectra have been analyzed to assign relative oxidation states to irons in the metalloclusters. The progress and challenges in this aspect of our work will be discussed. The results from the site-specific XAS studies on the MoFe-protein also demonstrate the presence of a mononuclear iron site, designated as Fe16, in addition to the fifteen iron sites present in the FeMo–cofactor and P–cluster. The Fe K-edge absorption data of the Fe16 site indicates that the iron is in the ferrous oxidation state. The high sequence conservation of the residues coordinated to Fe16 emphasizes the potential importance of the site in nitrogenase.

Additional Information

© 2017 SBIC.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023