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Published March 18, 2019 | Supplemental Material + Published
Journal Article Open

Site-specific oxidation state assignments of the irons in the [4Fe:4S]^(2+/1+/0) states of the nitrogenase Fe-protein

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 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.

Additional Information

© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Accepted manuscript online: 30 January 2019; Manuscript accepted: 18 January 2019; Manuscript received: 14 December 2018. We thank Prof. O. Einsle, Prof. L. Zhang, Dr. K. Perez, Dr. R. Arias, A. Maggiolo, and Prof. J. B. Howard for informative discussions, and K. H. Lee for the initial identification of the ADP‐bound Fe‐protein crystals. We acknowledge the Gordon and Betty Moore Foundation and the Beckman Institute at Caltech for their generous support of the Molecular Observatory at Caltech. We thank the staff at Beamline 12‐2, Stanford Synchrotron Radiation Lightsource (SSRL), operated for the DOE and supported by its OBER and by the NIH, NIGMS (P41GM103393), and the NCRR (P41RR001209). We also thank Dr. A. Di Bilio for assisting with EPR experiments. The Caltech EPR Facility was supported by NSF‐1531940. This work was supported by NIH grant GM045162 and the Howard Hughes Medical Institute. The authors declare no conflict of interest.

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Published - Wenke_et_al-2019-Angewandte_Chemie_International_Edition.pdf

Supplemental Material - anie201813966-sup-0001-misc_information.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 20, 2023