Catalytic activities of NifEN: Implications for nitrogenase evolution and mechanism
- 6 October 2009
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 106 (40), 16962-16966
- https://doi.org/10.1073/pnas.0907872106
Abstract
NifEN is a key player in the biosynthesis of nitrogenase MoFe protein. It not only shares a considerable degree of sequence homology with the MoFe protein, but also contains clusters that are homologous to those found in the MoFe protein. Here we present an investigation of the catalytic activities of NifEN. Our data show that NifEN is catalytically competent in acetylene (C(2)H(2)) and azide (N(3)(-)) reduction, yet unable to reduce dinitrogen (N(2)) or evolve hydrogen (H(2)). Upon turnover, C(2)H(2) gives rise to an additional S = 1/2 signal, whereas N(3)(-) perturbs the signal originating from the NifEN-associated FeMoco homolog. Combined biochemical and spectroscopic studies reveal that N(3)(-) can act as either an inhibitor or an activator for the binding and/or reduction of C(2)H(2), while carbon monoxide (CO) is a potent inhibitor for the binding and/or reduction of both N(3)(-) and C(2)H(2). Taken together, our results suggest that NifEN is a catalytic homolog of MoFe protein; however, it is only a "skeleton" version of the MoFe protein, as its associated clusters are simpler in structure and less versatile in function, which, in turn, may account for its narrower range of substrates and lower activities of substrate reduction. The resemblance of NifEN to MoFe protein in catalysis points to a plausible, sequential appearance of the two proteins in nitrogenase evolution. More importantly, the discrepancy between the two systems may provide useful insights into nitrogenase mechanism and allow reconstruction of a fully functional nitrogenase from the "skeleton" enzyme, NifEN.Keywords
This publication has 20 references indexed in Scilit:
- FeMo cofactor maturation on NifENProceedings of the National Academy of Sciences, 2006
- Evidence for a dynamic role for homocitrate during nitrogen fixation: the effect of substitution at the α-Lys426 position in MoFe-protein of Azotobacter vinelandiiBiochemical Journal, 2006
- Breaking the N2 triple bond: insights into the nitrogenase mechanismDalton Transactions, 2006
- Electron Inventory, Kinetic Assignment (En), Structure, and Bonding of Nitrogenase Turnover Intermediates with C2H2 and COJournal of the American Chemical Society, 2005
- Variant MoFe proteins of Azotobacter vinelandii: effects of carbon monoxide on electron paramagnetic resonance spectra generated during enzyme turnoverJBIC Journal of Biological Inorganic Chemistry, 2005
- Characterization of Azotobacter vinelandii nifZ Deletion StrainsJournal of Biological Chemistry, 2004
- Localization of a Substrate Binding Site on the FeMo-Cofactor in Nitrogenase: Trapping Propargyl Alcohol with an α-70-Substituted MoFe ProteinBiochemistry, 2003
- The FeMoco-deficient MoFe Protein Produced by a nifHDeletion Strain of Azotobacter vinelandii Shows Unusual P-cluster FeaturesJournal of Biological Chemistry, 2002
- Differential Effects on N2 Binding and Reduction, HD Formation, and Azide Reduction with α-195His- and α-191Gln-Substituted MoFe Proteins of Azotobacter vinelandii NitrogenaseBiochemistry, 2000
- The Azotobacter vinelandii NifEN Complex Contains Two Identical [4Fe-4S] ClustersBiochemistry, 1998