Nitrogenase Mechanisms and Enzymatic Functionality

Nitrogenases are multisubunit metalloenzymes responsible for the biological fixation of dinitrogen into ammonia, a process that underpins global nitrogen availability and agricultural productivity. The canonical molybdenum nitrogenase comprises two component proteins: the Fe protein, which hydrolyses ATP to deliver electrons, and the MoFe protein, which harbours two distinct metal clusters—the P-cluster and the FeMo-cofactor. Electron transfer from the Fe protein to the P-cluster and subsequently to the FeMo-cofactor is coupled to conformational changes and ATP hydrolysis, enabling stepwise reduction of inert N₂ under ambient conditions. The coordination environment of the FeMo-cofactor, including a homocitrate ligand, dictates substrate binding and activation. Alternative nitrogenases, containing vanadium or iron in place of molybdenum, reveal variations in activity and substrate specificity. Mechanistic insights have emerged from spectroscopic, structural and biochemical studies, illuminating dynamic changes in cluster oxidation states and transient binding intermediates. Advances in protein engineering and heterologous expression aim to overcome oxygen sensitivity and harness nitrogenase functionality for sustainable agriculture and bioindustrial ammonia production.

Research from Nature Portfolio

Recent structural analyses have revealed the dynamic nature of the FeMo-cofactor active site. Cryogenic electron microscopy of turnover-inactivated MoFe protein variants demonstrated that loss of the homocitrate ligand induces disordering of the cofactor and reorganisation of adjacent subunit domains, suggesting a repair or assembly role for auxiliary proteins. Spatially resolved anomalous dispersion refinement has clarified the resting-state electron distribution within the FeMo-cofactor, identifying distinct reduction levels among individual iron centres and corroborating revised oxidation-state assignments. In efforts to mitigate oxygen sensitivity, expression of the nitrogenase Fe protein targeted to the mitochondrial matrix of a eukaryotic host has yielded active enzyme under aerobic conditions, illustrating compartmentalisation as a strategy for functional assembly and offering a platform for future crop engineering.

Nitrogenase Mechanisms and Enzymatic Functionality publication trend

The graph below shows the total number of articles in nitrogenase mechanisms and enzymatic functionality across all publications each year (not limited to Nature Index journals).

Technical terms

Nitrogenase: An enzyme complex that catalyses ATP-dependent reduction of atmospheric N₂ to NH₃ in prokaryotic and engineered hosts.

FeMo-cofactor: The iron–molybdenum–sulphur cluster ([7Fe–1Mo–9S–1C] with homocitrate) at the active site of Mo nitrogenase enabling dinitrogen reduction.

P-cluster: An [8Fe–7S] metallocluster within the MoFe protein that mediates electron transfer from the Fe protein to the FeMo-cofactor.

Homocitrate: A citrate derivative coordinating to the molybdenum ion of the FeMo-cofactor, essential for stabilising the cluster and facilitating catalysis.

Metallocluster: A metal–sulphur assembly that forms the prosthetic groups of nitrogenase, responsible for electron storage and transfer during substrate conversion.

References

1. Structural consequences of turnover-induced homocitrate loss in nitrogenase. Nature Communications (2023).
2. Nitrogenase FeMoco investigated by spatially resolved anomalous dispersion refinement. Nature Communications (2016).
3. Expression of a functional oxygen-labile nitrogenase component in the mitochondrial matrix of aerobically grown yeast. Nature Communications (2016).
4. Biosynthesis of Nitrogenase Cofactors. Chemical Reviews (2020).
5. The Spectroscopy of Nitrogenases. Chemical Reviews (2020).
6. Expression of Active Subunit of Nitrogenase via Integration into Plant Organelle Genome. PLOS ONE (2016).
7. Comparative electronic structures of nitrogenase FeMoco and FeVco. Dalton Transactions (2017).