PMID:15485884

Citation	Hu, Y, Fay, AW, Dos Santos, PC, Naderi, F and Ribbe, MW (2004) Characterization of Azotobacter vinelandii nifZ deletion strains. Indication of stepwise MoFe protein assembly. J. Biol. Chem. 279:54963-71
Abstract	The nifZ gene product (NifZ) of Azotobacter vinelandii has been implicated in MoFe protein maturation. However, its exact function in this process remains largely unknown. Here, we report a detailed biochemical/biophysical characterization of His-tagged MoFe proteins purified from A. vinelandii nifZ and nifZ/nifB deletion strains DJ1182 and YM6A (Delta nifZ and Delta nifZ Delta nifB MoFe proteins, respectively). Our data from EPR, metal, activity, and stability analyses indicate that one alpha beta subunit pair of the Delta nifZ MoFe protein contains a P cluster ([8Fe-7S]) and an iron-molybdenum cofactor (FeMoco) ([Mo-7Fe-9S-X-homocitrate]), whereas the other contains a presumed P cluster precursor, possibly comprising a pair of [4Fe-4S]-like clusters, and a vacant FeMoco site. Likewise, the Delta nifZ Delta nifB MoFe protein has the same composition as the Delta nifZ MoFe protein except for the absence of FeMoco, an effect caused by the deletion of the nifB gene. These results suggest that the MoFe protein is likely assembled stepwise, i.e. one alpha beta subunit pair of the tetrameric MoFe protein is assembled prior to the other, and that NifZ might act as a chaperone in the assembly of the second alpha beta subunit pair by facilitating a conformational rearrangement that is required for the formation of the P cluster through the condensation of two [4Fe-4S]-like clusters. The possibility of NifZ exercising its effect through the Fe protein was ruled out because the Fe proteins from nifZ and nifZ/nifB deletion strains are not defective in their normal functions. However, the detailed mechanism of how NifZ carries out its exact function in MoFe protein maturation awaits further investigation.
Links	PubMed Online version:10.1074/jbc.M408983200
Keywords	Azotobacter vinelandii/chemistry; Azotobacter vinelandii/genetics; Azotobacter vinelandii/growth & development; Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Bacterial Proteins/physiology; Catalysis; Chemistry, Physical; Electron Spin Resonance Spectroscopy; Gene Deletion; Genes, Bacterial; Histidine; Molybdoferredoxin/chemistry; Molybdoferredoxin/genetics; Nitrogen Fixation/genetics; Physicochemical Phenomena; Protein Conformation; Protein Subunits/chemistry; Protein Subunits/genetics
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
AZOVI:NIFZ	involved_in	GO:0009399: nitrogen fixation	ECO:0000315: mutant phenotype evidence used in manual assertion		P		Seeded From UniProt	complete
AZOVI:NIFZ		GO:0009399: nitrogen fixation	ECO:0000315:		P		Tables 3 and 4	complete CACAO 8544

References

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