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Abstract

Nitrogenases are best known for catalysing the reduction of dinitrogen to ammonia at a complex metallic cofactor. Recently, nitrogenases were shown to reduce carbon dioxide (CO2) and carbon monoxide to hydrocarbons, offering a pathway to recycle carbon waste into hydrocarbon products. Among the nitrogenase family the iron nitrogenase is the isozyme with the highest wildtype activity for the reduction of CO2, but the molecular architecture facilitating these activities remained unknown. Here, we report a 2.35-Å cryogenic electron microscopy structure of the Fe nitrogenase complex from Rhodobacter capsulatus, revealing an [Fe8S9C-(R)-homocitrate]-cluster in the active site. The enzyme complex suggests that the AnfG-subunit is involved in cluster stabilisation, substrate channelling and confers specificity between nitrogenase reductase and catalytic components. Moreover, the structure highlights a different interface between the two catalytic halves of the iron and the molybdenum nitrogenase, potentially influencing the intra-subunit ‘communication’ and thus the nitrogenase mechanism.Competing Interest StatementThe authors have declared no competing interest.