Nitrogenase MoFe protein cofactor

Fig. 7. View of the FeMo-cofactor prosthetic group of the nitrogenase MoFe protein with some of the surrounding amino acid residues where ( ) represents the molybdenum coordinated to a-His-442 and homocitrate (at the top), ( ) represents the iron, interspersed with the sulfur (O) and carbon...

Schmid B, Ribbe MW, Einsle O, et al. Structure of a Cofactor-Deficient Nitrogenase MoFe Protein. Science 2002 296 352-6. 

Einsle O, Tezcan FA, Andrade SL, et al. Nitrogenase MoFe-protein at 1.16 A resolution A central ligand in the FeMo-cofactor. Science 2002 297 1696-700. 

Figure 12 35 GHz Fe and H CW ENDOR spectra of the hi-CO form of nitrogenase MoFe protein with varying types of Fe-enrichment. The H signals are included as intensity standards since the natural ahundance samples contain ohservahle amounts of Fe. The spectra were recorded at gobs = 2.06 (gj ). Cartoons on the left indicate the specific sample, wherein the FeMo-cofactor is indicated hy the diamond shape (in green), and the P-cluster is indicated by the two cubes (in red). These shapes roughly represent the clusters actual strucmres. Fe-enriched sites are indicated as colored blocks. The abbreviations used are as follows M(56)P(56) is natural abundance FeMo-cofactor and P-cluster M(56)P(57) is natural abundance FeMo-cofactor and enriched P-cluster M(57)P(56) is enriched FeMo-cofactor and natural abundance P-cluster M(57)P(57) is enriched FeMo-cofactor and P-cluster (i.e., globally enriched MoFe protein). (Adapted from Figure 1 in Christie, Lee, Cameron, Hales, Orme-Johnson and Hoffman. Reprinted with permission, 1996 American Chemical Society)...

The MoFe cofactor of the nitrogenase MoFe-protein component... 

Bolin JT, Campobasso N, Muchmoee SW, Morgan TV and Moetenson LE (1993) The structure and environment of the metal clusters in the nitrogenase MoFe protein from Clostridium pasteurianum. In Stiefel El, Coucouvanis D and Newton WE, eds. Molybdenum enzymes, cofactors and model systems, pp. 186-195. American Chemical Society, Washington, D. C. 

As well as donating electrons to the MoFe protein, the Fe protein has at least two and possibly three other functions (see Section IV,C) It is involved in the biosynthesis of the iron molybdenum cofactor, FeMoco it is required for insertion of the FeMoco into the MoFe protein polypeptides and it has been implicated in the regulation of the biosynthesis of the alternative nitrogenases. 

Fig. 1. Schematic illustration of the enzyme nitrogenase being composed of the molybdenum-iron (MoFe) protein, an oc2p2 tetramer with two unique iron-sulfur clusters (P-cluster) and two iron-molybdenum cofactors (FeMoco), and the iron protein with one [4Fe-4S]-cluster and two ATP binding sites.

Figure 3.28 The FeMo cofactor, M center, of nitrogenase s MoFe protein.

The P clusters of nitrogenase. The enzyme nitrogenase consists of two proteins the Fe protein (m.w. 55,000), which contains a single 4Fe-4S center, and the more complex MoFe protein (m.w. 220,000) (48,49). The minimum functional unit of the latter appears to be the half molecule, an asymmetric dimer containing 1 Mo, 14-16 Fe, and 16-18 sulfides. Application of a vast array of spectroscopic methods to the MoFe protein in a variety of oxidation states has led to the conclusion that it contains two types of metal-sulfur cluster in a 2 1 ratio unusual Fe S units termed P clusters, and the protein-bound form of the FeMo-cofactor (50). 

The other subunit of nitrogenase, the MoFe-protein, has acquired more attention. A centre called P-cluster comprising a [FegS7] centre together with the [Fe7S9Mo-homocitrate] complex denoted FeMo-cofactor or M-centre are located in this part. The interplay between the Fe- and the MoFe-protein parts... 

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