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Site‐Specific Oxidation State Assignments of the Iron Atoms in the [4Fe:4S] 2+/1+/0 States of the Nitrogenase Fe‐Protein
Author(s) -
Wenke Belinda B.,
Spatzal Thomas,
Rees Douglas C.
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201813966
Subject(s) - nitrogenase , oxidation state , delocalized electron , chemistry , redox , crystallography , valence (chemistry) , ferredoxin , molybdenum , electron transfer , dithionite , inorganic chemistry , photochemistry , metal , nitrogen fixation , organic chemistry , nitrogen , biochemistry , enzyme
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 Fe 2.5+ pair and a buried Fe 2+ 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 Fe 2+ and valence delocalized Fe 2.5+ , respectively.