NIFn

NifN is a nitrogen fixation gene encoding a protein that participates in the biosynthesis of the nitrogenase FeMo-cofactor in certain bacteria and archaea. The NifN protein is typically found in nif gene clusters together with other nitrogenase components, such as nifH, nifD, nifK, and nifE. Like NifE, NifN is a paralog of the dinitrogenase subunits and shares structural similarity with the MoFe protein components.

NifN forms a complex with NifE, and this NifN-NifE scaffold supports the maturation of the FeMo-cofactor on a NifB-derived precursor. The FeMo-co is essential for catalytic reduction of N2 by the MoFe protein NifDK. The precise mechanism is complex, but NifN/NifE are thought to guide assembly and stabilize intermediates and to enable eventual transfer of the mature cofactor to NifDK.

Expression of nifN is typically regulated by NifA and other regulatory factors in response to nitrogen limitation and oxygen tension in diazotrophs. Disruption of nifN impairs proper FeMo-co formation and nitrogenase activity, leading to reduced nitrogen fixation.

NifN homologs occur in many bacterial nitrogen-fixers, including free-living and symbiotic organisms. The study of NifN and related proteins has provided key insights into how the FeMo-cofactor is assembled and inserted into the nitrogenase active site.

See also nitrogenase, NifE, NifB.