5c2v
Kuenenia stuttgartiensis Hydrazine Synthase
Structural highlights
FunctionHZSA_KUEST Component of the hydrazine synthase complex that catalyzes the condensation of nitric oxide (NO) with ammonium to form hydrazine (PubMed:21964329). The alpha subunit catalyzes the second half-reaction, i.e. the condensation of hydroxylamine formed in the active site of the gamma subunit with ammonia, yielding hydrazine (PubMed:26479033). Is involved in anaerobic ammonium oxidation (anammox), a biological process in which nitrite is used as the electron acceptor in the conversion of ammonium to dinitrogen gas (N2) and water; this bacterial process has a major role in the Earth's nitrogen cycle and has been estimated to synthesize up to 50% of the dinitrogen gas emitted into our atmosphere from the oceans (PubMed:21964329, PubMed:26479033).[1] [2] Publication Abstract from PubMedAnaerobic ammonium oxidation (anammox) has a major role in the Earth's nitrogen cycle and is used in energy-efficient wastewater treatment. This bacterial process combines nitrite and ammonium to form dinitrogen (N2) gas, and has been estimated to synthesize up to 50% of the dinitrogen gas emitted into our atmosphere from the oceans. Strikingly, the anammox process relies on the highly unusual, extremely reactive intermediate hydrazine, a compound also used as a rocket fuel because of its high reducing power. So far, the enzymatic mechanism by which hydrazine is synthesized is unknown. Here we report the 2.7 A resolution crystal structure, as well as biophysical and spectroscopic studies, of a hydrazine synthase multiprotein complex isolated from the anammox organism Kuenenia stuttgartiensis. The structure shows an elongated dimer of heterotrimers, each of which has two unique c-type haem-containing active sites, as well as an interaction point for a redox partner. Furthermore, a system of tunnels connects these active sites. The crystal structure implies a two-step mechanism for hydrazine synthesis: a three-electron reduction of nitric oxide to hydroxylamine at the active site of the gamma-subunit and its subsequent condensation with ammonia, yielding hydrazine in the active centre of the alpha-subunit. Our results provide the first, to our knowledge, detailed structural insight into the mechanism of biological hydrazine synthesis, which is of major significance for our understanding of the conversion of nitrogenous compounds in nature. The inner workings of the hydrazine synthase multiprotein complex.,Dietl A, Ferousi C, Maalcke WJ, Menzel A, de Vries S, Keltjens JT, Jetten MS, Kartal B, Barends TR Nature. 2015 Nov 19;527(7578):394-7. doi: 10.1038/nature15517. Epub 2015 Oct 19. PMID:26479033[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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