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A V‐Nitrogenase Variant Containing a Citrate‐Substituted Cofactor
Author(s) -
Newcomb Megan P.,
Lee Chi Chung,
Tanifuji Kazuki,
Jasniewski Andrew J.,
Liedtke Jasper,
Ribbe Markus W.,
Hu Yilin
Publication year - 2020
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.201900654
Subject(s) - nitrogenase , azotobacter vinelandii , cofactor , chemistry , dimer , ligand (biochemistry) , catalysis , stereochemistry , protein subunit , substrate (aquarium) , medicinal chemistry , nitrogen fixation , enzyme , biochemistry , nitrogen , organic chemistry , biology , receptor , gene , ecology
Nitrogenases catalyze the ambient reduction of N 2 and CO at its cofactor site. Herein we present a biochemical and spectroscopic characterization of an Azotobacter vinelandii V nitrogenase variant expressing a citrate‐substituted cofactor. Designated VnfDGK Cit , the catalytic component of this V nitrogenase variant has an αβ 2 (δ) subunit composition and carries an 8Fe P* cluster and a citrate‐substituted V cluster analogue in the αβ dimer, as well as a 4Fe cluster in the “orphaned” β‐subunit. Interestingly, when normalized based on the amount of cofactor, VnfDGK Cit shows a shift of N 2 reduction from H 2 evolution toward NH 3 formation and an opposite shift of CO reduction from hydrocarbon formation toward H 2 evolution. These observations point to a role of the organic ligand in proton delivery during catalysis and imply the use of different reaction sites/mechanisms by nitrogenase for different substrate reductions. Moreover, the increased NH 3 /H 2 ratio upon citrate substitution suggests the possibility to modify the organic ligand for improved ammonia synthesis in the future.