Site-Specific Oxidation State Assignments of the Iron Atoms in the [4Fe:4S]2+/1+/0 States of the Nitrogenase Fe-Protein

Angew Chem Int Ed Engl. 2019 Mar 18;58(12):3894-3897. doi: 10.1002/anie.201813966. Epub 2019 Feb 14.

Abstract

The nitrogenase iron protein (Fe-protein) contains an unusual [4Fe:4S] iron-sulphur cluster that is stable in three oxidation states: 2+, 1+, and 0. Here, we use spatially resolved anomalous dispersion (SpReAD) refinement to determine oxidation assignments for the individual irons for each state. Additionally, we report the 1.13-Å resolution structure for the ADP bound Fe-protein, the highest resolution Fe-protein structure presently determined. In the dithionite-reduced [4Fe:4S]1+ state, our analysis identifies a solvent exposed, delocalized Fe2.5+ pair and a buried Fe2+ pair. We propose that ATP binding by the Fe-protein promotes an internal redox rearrangement such that the solvent-exposed Fe pair becomes reduced, thereby facilitating electron transfer to the nitrogenase molybdenum iron-protein. In the [4Fe:4S]0 and [4Fe:4S]2+ states, the SpReAD analysis supports oxidation states assignments for all irons in these clusters of Fe2+ and valence delocalized Fe2.5+ , respectively.

Keywords: X-ray crystallography; iron-sulphur cluster; multiple-wavelength anomalous diffraction; nitrogenase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Diphosphate / chemistry
  • Adenosine Diphosphate / metabolism
  • Biocatalysis
  • Electron Spin Resonance Spectroscopy
  • Hydrogen Bonding
  • Ions / chemistry
  • Iron / chemistry*
  • Iron-Sulfur Proteins / chemistry
  • Iron-Sulfur Proteins / metabolism
  • Molybdenum / chemistry
  • Oxidation-Reduction
  • Oxidoreductases / chemistry
  • Oxidoreductases / metabolism*

Substances

  • Ions
  • Iron-Sulfur Proteins
  • Adenosine Diphosphate
  • Molybdenum
  • Iron
  • Oxidoreductases
  • nitrogenase reductase