Catalysis-dependent selenium incorporation and migration in the nitrogenase active site iron-molybdenum cofactor

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Cite this article as: eLife 2015;4:e11620 doi: 10.7554/eLife.11620

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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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Author details

Thomas Spatzal

Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, United States

Competing interests
The authors declare that no competing interests exist.
Kathryn A Perez

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, United States

Competing interests
The authors declare that no competing interests exist.
James B Howard

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, United States

Competing interests
The authors declare that no competing interests exist.
Douglas C Rees

Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, United States

For correspondence
dcrees@caltech.edu

Competing interests
The authors declare that no competing interests exist.

Reviewing Editor

Wilfred A van der Donk, University of Illinois at Urbana-Champaign, United States

Publication history

Received: September 15, 2015
Accepted: December 15, 2015
Accepted Manuscript published: December 16, 2015 (version 1)
Version of Record published: February 3, 2016 (version 2)

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.