Research in the laboratory of Prof. Luis Rubio aims at understanding the biochemical processes and mechanisms that enable biological N2 fixation, the reduction of inert N2 gas into ammonia. A long-term goal of this research, supported by the Bill & Melinda Foundation, is to obtain crops that can utilize atmospheric N2 as direct nitrogen source, minimizing the need of synthetic nitrogen fertilizers, one of the main expenses for farmers and prohibitively so in developing countries, and reducing the negative environmental effects that originates from fertilizer production and use.
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.