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Structural insights into metallocluster trafficking in the nitrogenase assembly scaffold NifEN
Bryan Neumann1, Kristal A Brandon1, Robert Quechol1
1Department of Molecular Biology and Biochemistry, University of California, Irvine, CA USA.
Nature Catalysis
|March 30, 2026
Summary
Researchers used cryo-EM to study NifEN, a protein crucial for nitrogenase cofactor assembly. They discovered a dynamic tunnel mechanism for metallocluster trafficking, advancing our understanding of this vital biological process.
Area of Science:
- Biochemistry and Structural Biology
- Nitrogen Fixation and Metalloenzymes
Background:
- Nitrogenase is essential for small-molecule activation, with significant implications for agriculture, environmental science, and energy.
- Understanding the assembly of the complex nitrogenase cofactor is a long-standing challenge, with limited structural data available.
Purpose of the Study:
- To elucidate the structural mechanisms of nitrogenase cofactor assembly, focusing on the role of the NifEN protein.
- To investigate the conformational changes and metallocluster trafficking mediated by NifEN during cofactor maturation.
Main Methods:
- Cryogenic electron microscopy (cryo-EM) was employed to determine high-resolution structures of NifEN.
- Apo- and holo-NifEN structures, along with complexes involving NifB and NifH, were analyzed.
- Supporting techniques included mutational studies, AlphaFold 3 predictions, and negative-stain EM.
Main Results:
- Major conformational changes in NifEN were observed upon L-cluster incorporation, indicating dynamic structural rearrangements.
- Structures revealed distinct NifEN conformations with inwardly and outwardly bound L-clusters.
- A tunnel connecting NifEN with NifB and NifH was identified, facilitating metallocluster transfer.
Conclusions:
- NifEN acts as a dynamic hub, coordinating the reception, maturation, and delivery of the L-cluster.
- Conformation-gated metallocluster trafficking through a tunnel mechanism is proposed for nitrogenase cofactor assembly.
- These findings provide crucial structural insights into a fundamental process in nitrogen fixation.
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