Biosynthesis of Nitrogenase Cofactors

Biological N2 fixation relies on O2-sensitive metalloenzymes called nitrogenases (called Fe protein and MoFe protein). Nitrogenase harbors three distinct metal prosthetic groups that are required for its activity. The simplest one is a [4Fe-4S] cluster located at the Fe protein nitrogenase component. The MoFe protein component carries an [8Fe-7S] group called P-cluster and a [7Fe-9S-C-Mo-R-homocitrate] group called FeMo-co.

About 20 nitrogen fixation gene products are involved in maturation and functionality of the nitrogenase enzyme. Importantly, formation of the nitrogenase metalloclusters requires the both participation of the structural nitrogenase components as well as many accessory proteins. While formation of the P-cluster happens in situ at the MoFe protein, the biosynthesis of FeMo-co is performed stepwise and involves molecular scaffolds, metallochaperones, radical chemistry, and novel and unique biosynthetic intermediates. This review provides a comprehensive and critical overview of the discoveries on nitrogenase cofactor structure, function and activity over the last four decades, and highlights areas that will require further attention in order to transfer the complete nitrogenase molecular machinery into eukaryotes, such as plants.