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E2. The Structure of Nitrogenase

  • Page ID
    5716
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    Nitrogenase is a multiprotein complex containing the following:

    • Two identical subunits, E and F, which have binding sites for the mobile carrier of electrons (the protein ferrodoxin or flavodoxin), ATP, and an FeS cofactor (4Fe-4S, called the F cluster) which accept electrons. These subunits are hence called the nitrogenase reducatase subunits

    • a heterodimer of an alpha and beta subunits. The a (alpha chain) binds the 8Fe-7S F cluster and the Fe-S-Mo M cluster. These subunits comprise the (di)nitrogenase subunits

    The overall structure of the protein complex with bound ATP and metal centers are shown below.

    nitrogenase_tot_struct_2annotated.png

    An interactive Jsmol structure of nitrogenase is found in the link below.

    iconChime.gif JSMol (HTML5)

    Protopedia: Nitrogenase

    An enhanced view of the bound cofactors and ATP are shown in the same spatial orientation in the figure below.

    nitrogenase_metcenter_ATP_annotated.png

    The metal centers are shown below in more detail in both line and space fill views.

    MetalClustersNitrogenase.png

    Mo is bound to 3 sulfur ions and two a OH and carboxyl group of 3-hydroxy-3-carboxy, adipic acid in the crystal structure of shown above.

    The M cluster has an interstitial carbide ion that derives from -CH3 attached to the sulfur of S-adenosyl-methionine (SAM) allowing the carbide to be labeled with either 13C or 14C for mechanistic studies. These labeled carbides are not exchanged or used as a substrate when the enzyme undergoes catalytic turnover. Hence it seems that the carbide probably just stabilizes the M cluster. it won't be shown in the figures below showing more detailed mechanisms.

    Contributors


    This page titled E2. The Structure of Nitrogenase is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Henry Jakubowski.

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