Catalysis-dependent selenium incorporation and migration in the nitrogenase active site iron-molybdenum cofactor
- Howard Hughes Medical Institute, California Institute of Technology, United States
- California Institute of Technology, United States
Abstract
Dinitrogen reduction in the biological nitrogen cycle is catalyzed by nitrogenase, a two-component metalloenzyme. Understanding of the transformation of the inert resting state of the active site FeMo-cofactor into an activated state capable of reducing dinitrogen remains elusive. Here we report the catalysis dependent, site-selective incorporation of selenium into the FeMo-cofactor from selenocyanate as a newly identified substrate and inhibitor. The 1.60 Å resolution structure reveals selenium occupying the S2B site of FeMo-cofactor in the Azotobacter vinelandii MoFe-protein, a position that was recently identified as the CO-binding site. The Se2B-labeled enzyme retains substrate reduction activity and marks the starting point for a crystallographic pulse-chase experiment of the active site during turnover. Through a series of crystal structures obtained at resolutions of 1.32-1.66 Å, including the CO-inhibited form of Av1-Se2B, the exchangeability of all three belt-sulfur sites is demonstrated, providing direct insights into unforeseen rearrangements of the metal center during catalysis.
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© 2015, Spatzal et al.
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Catalysis-dependent selenium incorporation and migration in the nitrogenase active site iron-molybdenum cofactor
eLife 4:e11620.
https://doi.org/10.7554/eLife.11620
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