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The Nitrogenase FeMo‐Cofactor Precursor Formed by NifB Protein: A Diamagnetic Cluster Containing Eight Iron Atoms
Author(s) -
Guo Yisong,
EchavarriErasun Carlos,
Demuez Marie,
JiménezVicente Emilio,
Bominaar Emile L.,
Rubio Luis M.
Publication year - 2016
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201606447
Subject(s) - chemistry , cofactor , nitrogenase , crystallography , cluster (spacecraft) , hyperfine structure , mössbauer spectroscopy , stereochemistry , biochemistry , enzyme , atomic physics , organic chemistry , nitrogen fixation , physics , computer science , nitrogen , programming language
The biological activation of N 2 occurs at the FeMo‐cofactor, a 7Fe–9S–Mo–C–homocitrate cluster. FeMo‐cofactor formation involves assembly of a Fe 6–8 –S X –C core precursor, NifB‐co, which occurs on the NifB protein. Characterization of NifB‐co in NifB is complicated by the dynamic nature of the assembly process and the presence of a permanent [4Fe–4S] cluster associated with the radical SAM chemistry for generating the central carbide. We have used the physiological carrier protein, NifX, which has been proposed to bind NifB‐co and deliver it to the NifEN protein, upon which FeMo‐cofactor assembly is ultimately completed. Preparation of NifX in a fully NifB‐co‐loaded form provided an opportunity for Mössbauer analysis of NifB‐co. The results indicate that NifB‐co is a diamagnetic ( S =0) 8‐Fe cluster, containing two spectroscopically distinct Fe sites that appear in a 3:1 ratio. DFT analysis of the 57 Fe electric hyperfine interactions deduced from the Mössbauer analysis suggests that NifB‐co is either a 4Fe 2+ –4Fe 3+ or 6Fe 2+ –2Fe 3+ cluster having valence‐delocalized states.