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Nitrogenase.

This page shows some interactive JSmol views of the nitrogen-fixing enzyme nitrogenase.

The first figure shows an overview of the nitrogenase assembly. It contains two "Fe protein" units (top and bottom) that contain ADP and a [4Fe-4S] cluster. The central part comprises the "MoFe protein".

The next figure shows the structure of the MoFe protein from Azobacter vinelandii. The protein contains 4 chains (each shown in a different colour);two contain FeS clusters and two contain the FeMo active site.



One of the subunits containing an Fe8S7 cluster ("the P cluster") is shown in the next figure, with a close-up view of the cluster on the next button. Note that the cluster contains 8 iron ions, 7 inorganic S2- ions and 6 Cysteine residues; three of the Cys ligands are from another chain and one of them (unusually) binds as a bidentate ligand, using the amide nitrogen atom. This cluster is clearly related to other iron-sulfur proteins and likely to be an electron transfer site.



The next set of figures shows the chain containing the FeMo active site and close up views of the active site with and without the protein.

The "MoFe cofactor" active site contains 7 Fe ions, 1 Mo and 9 S2- ions; one Cys and one His residue from the protein are bonded to an iron and a molybedenum, respectively and a citrate anion is also coordinated to the Mo. Finally, the atom at the centre of the cluster has been identified as a (6-coordinate) carbon.
The figure "MoFe with N2" is taken from a recent (2020) structure determination and shows two dinitrogen species bound at the active site i.e. trapped just before the N2 molecules are released. Note that this interpretation of the crystallographic data has been questioned (see JBIC (2021) 26:341–353 or Science, 371 (6530), eabe5481) and may not be correct.

The final figure shows both clusters, to give an idea of their proximity to one another.

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Based on template by A. Herráez as modified by J. Gutow and V. McKee updated October 2021.
This will be the viewer still of jmol image
Nitrogenase from Azotobacter vinelandii data from: Evidence for interstitial carbon in nitrogenase FeMo cofactor. Spatzal T, Aksoyoglu M, Zhang L, Andrade SL, Schleicher E, Weber S, Rees DC, Einsle O Science 334 940 (2011) (PDB code 3U7Q).
Larger complex from Structure of ADP x AIF4(-)-stabilized nitrogenase complex and its implications for signal transduction. Schindelin, H., Kisker, C., Schlessman, J.L., Howard, J.B., Rees, D.C. (1997) Nature 387: 370-376 (PDB code 1N2C)
N2 data from: Structural evidence for a dynamic metallocofactor during N2reduction by Mo-nitrogenase. Kang, W., Lee, C.C., Jasniewski, A.J., Ribbe, M.W., Hu, Y. (2020) Science 368: 1381-1385 (PDB code 6UGO) Return to the index page.