Nitrogenases biosynthesis

STRUCTURE, FUNCTION, AND BIOSYNTHESIS OF THE METALLOSULFUR CLUSTERS IN NITROGENASES... 

These were relatively low-resolution structures, and with refinement some errors in the initial structural assignments have been detected (4-7). Since the structures were first reported the subject has been extensively reviewed in this series (8) and elsewhere 9-15). This review will focus on the structure, biosynthesis, and function of the met-allosulfur clusters found in nitrogenases. This will require a broader overview of some functional aspects, particularly the involvement of MgATP in the enzymic reaction, and also some reference will be made to the extensive literature (9, 15) on biomimetic chemistry that has helped to illuminate possible modes of nitrogenase function, although a detailed review of this chemistry will not be attempted here. This review cannot be fully comprehensive in the space available, but concentrates on recent advances and attempts to describe the current level of our understanding. 

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. 

NifM is required for maturation of VnfH, and NifS and U seem to be important for provision of sulfide and probably iron for the biosynthesis of the vanadium nitrogenase. The apo VFe protein has been isolated from an A. vinelandii strain deleted for nifKD and nifB (169). It was an hexamer that could be activated in vitro by the addi-... 

A great deal has been learned about the biosynthesis of nitrogenases, but at the moment the process is understood only in broad outline. The detailed roles of the individual gene products require much further investigation, which may once more indicate fresh approaches to some of the problems identified herein. In particular, if the biosynthetic steps can be emulated chemically, then it may be possible to synthesize FeMoco in large quantities in order to allow its detailed analysis at the atomic level. 

Structure, Function, and Biosynthesis of the Metallosulfur Clusters in Nitrogenases Barry E. Smith... 

This review is a summary of our recent genetic, biochemical, and biophysical, studies of the Fe-S cluster assembly proteins of A. vinelandii, with particular emphasis on the role of the NifU and IscU proteins. The results reveal insight into the mechanism of both general and nitrogenase-specific Fe-S cluster biosynthesis in A. vinelandii and indicate a common mechanism for Fe-S cluster assembly that is used throughout nature. 

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