A bound reaction intermediate sheds light on the mechanism of nitrogenase

作者：Sippel, Daniel; Rohde, Michael; Netzer, Julia; Trncik, Christian; Gies, Jakob; Grunau, Katharina; Djurdjevic, Ivana; Decamps, Laure; Andrade, Susana L. A.; Einsle, Oliver^*

来源：Science, 2018, 359(6383): 1484-+.

DOI：10.1126/science.aar2765

• KLEBSIELLA-PNEUMONIAE NITROGENASE
• IRON-MOLYBDENUM COFACTOR
• FEMO-COFACTOR
• N-2 REDUCTION
• VANADIUM-NITROGENASE
• ACETYLENE-REDUCTION
• ENDOR SPECTROSCOPY
• REACTION PATHWAY
• KINETIC SCHEME
• H-2 EVOLUTION

Reduction of N-2 by nitrogenases occurs at an organometallic iron cofactor that commonly also contains either molybdenum or vanadium. The well-characterized resting state of the cofactor does not bind substrate, so its mode of action remains enigmatic. Carbon monoxide was recently found to replace a bridging sulfide, but the mechanistic relevance was unclear. Here we report the structural analysis of vanadium nitrogenase with a bound intermediate, interpreted as a mu(2)-bridging, protonated nitrogen that implies the site and mode of substrate binding to the cofactor. Binding results in a flip of amino acid glutamine 176, which hydrogen-bonds the ligand and creates a holding position for the displaced sulfide. The intermediate likely represents state E-6 or E-7 of the Thorneley-Lowe model and provides clues to the remainder of the catalytic cycle.

• 出版日期2018-3-30