Biosynthesis of the Metalloclusters of Nitrogenases

Abstract

Nitrogenase is a versatile metalloenzyme that is capable of catalyzing two important reactions under ambient conditions: the reduction of nitrogen (N2) to ammonia (NH3), a key step in the global nitrogen cycle; and the reduction of carbon monoxide (CO) and carbon dioxide (CO2) to hydrocarbons, two reactions useful for recycling carbon waste into carbon fuel. The molybdenum (Mo)- and vanadium (V)-nitrogenases are two homologous members of this enzyme family. Each of them contains a P-cluster and a cofactor, two high-nuclearity metalloclusters that have crucial roles in catalysis. This review summarizes the progress that has been made in elucidating the biosynthetic mechanisms of the P-cluster and cofactor species of nitrogenase, focusing on what is known about the assembly mechanisms of the two metalloclusters in Mo-nitrogenase and giving a brief account of the possible assembly schemes of their counterparts in V-nitrogenase, which are derived from the homology between the two nitrogenases.

Synthetic Analogues of Nitrogenase Metallocofactors: Challenges and Developments

“…The presence of the interstitial μ 6 ‐C atom is arguably the most fascinating and synthetically challenging aspect of the M‐cluster structure. This central atom is incorporated at an important juncture in nitrogenase cofactor biosynthesis, representing the deviation from canonical [Fe 4 S 4 ] clusters to the unique [Fe 8 S 9 C] composition of the L ‐cluster, which is believed to be a shared precursor of the M‐, V‐, and Fe‐only‐clusters . Nitrogenase accomplishes C‐atom insertion on the protein NifB using the sacrificial cofactor S‐adenosylmethionine, which functions as both a methylating and C−H bond‐activating reagent .…”

Heterologous Expression and Engineering of the Nitrogenase Cofactor Biosynthesis Scaffold NifEN

“…Designated the M‐cluster (or FeMoco), the cofactor of Mo‐nitrogenase is a complex [( R ‐homocitrate)MoFe 7 S 9 C] cluster that is unique in biology and unprecedented in chemistry. The biosynthesis of the M‐cluster (Figure a) is a highly complex process and encompasses all components required for the assembly of a functional Mo‐nitrogenase. It begins with the concerted action of NifS and NifU, which mobilize Fe and S for the synthesis of [Fe 4 S 4 ] clusters.…”

Coordinated regulation of nitrogen fixation and molybdate transport by molybdenum

“…Mo mobilization for FeMoco assembly is mediated by NifQ. For details on Moco and FeMoco biosynthesis, see recent reviews (Hu and Ribbe, ; Curatti and Rubio, ; Yang et al , ; Mendel and Leimkühler, ; Hu and Ribbe, ; Leimkühler, ). VFeco and FeFeco are structurally similar to FeMoco but differ in several aspects.…”

“…Fe-protein delivers electrons one at a time and each Fe-protein cycle consumes two MgATP molecules (Burgess and Lowe, 1996). In contrast to all other molybdoenzymes, Mo-nitrogenase contains the unique iron-molybdenum cofactor, FeMoco (Hu and Ribbe, 2011;Curatti and Rubio, 2014;Hu and Ribbe, 2016). Biosynthesis of FeMoco involves the proteins NifS, NifU, NifB, NifE, NifN, NifQ, NifV and NifH (Fig.…”

“…To cope with Mo limitation, 89% of Mo-utilizing bacteria, regardless of whether diazotrophic or not, are predicted to synthesize highly efficient ModABC transporters (Peng et al, 2018). They import molybdate (MoO 4 2-), the only (Hu and Ribbe, 2011;Curatti and Rubio, 2014;Yang et al, 2014;Mendel and Leimkühler, 2015;Hu and Ribbe, 2016;Leimkühler, 2017). VFeco and FeFeco are structurally similar to FeMoco but differ in several aspects.…”