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Publication Abstract from PubMed

Nitrogenase catalyzes the ATP-dependent reduction of dinitrogen to ammonia during the process of biological nitrogen fixation that is essential for sustaining life. The active site FeMo-cofactor contains a [7Fe:1Mo:9S:1C] metallocluster coordinated with an R-homocitrate (HCA) molecule. Here, we establish through single particle cryoEM and chemical analysis of two forms of the Azotobacter vinelandii MoFe-protein - a high pH turnover inactivated species and a ∆NifV variant that cannot synthesize HCA - that loss of HCA is coupled to alpha-subunit domain and FeMo-cofactor disordering, and formation of a histidine coordination site. We further find a population of the ∆NifV variant complexed to an endogenous protein identified through structural and proteomic approaches as the uncharacterized protein NafT. Recognition by endogenous NafT demonstrates the physiological relevance of the HCA-compromised form, perhaps for cofactor insertion or repair. Our results point towards a dynamic active site in which HCA plays a role in enabling nitrogenase catalysis by facilitating activation of the FeMo-cofactor from a relatively stable form to a state capable of reducing dinitrogen under ambient conditions.

Structural consequences of turnover-induced homocitrate loss in nitrogenase.,Warmack RA, Maggiolo AO, Orta A, Wenke BB, Howard JB, Rees DC Nat Commun. 2023 Feb 25;14(1):1091. doi: 10.1038/s41467-023-36636-4. PMID:36841829^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.