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Characterization of anammox hydrazine dehydrogenase, a key N2-producing enzyme in the global nitrogen cycle

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Authors

  • Wouter J. Maalcke
  • Joachim Reimann
  • Simon de Vries
  • Julea N. Butt
  • Andreas Dietl
  • Nardy Kip
  • Ulrike Mersdorf
  • Thomas R. M. Barends
  • Mike S. M. Jetten
  • Jan T. Keltjens
  • Boran Kartal

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Abstract

Anaerobic ammonium-oxidizing (anammox) bacteria derive their energy for growth from the oxidation of ammonium with nitrite as the electron acceptor. N2, the end product of this metabolism, is produced from the oxidation of the intermediate, hydrazine (N2H4). Previously, we identified N2-producing hydrazine dehydrogenase (KsHDH) from the anammox organism Kuenenia stuttgartiensis as the gene product of kustc0694 and determined some of its catalytic properties. In the genome of K. stuttgartiensis, kustc0694 is one out of ten paralogs related to octaheme hydroxylamine (NH2OH) oxidoreductase (HAO). Here, we characterized KsHDH as a covalently cross-linked homotrimeric octaheme protein as found for HAO and HAOrelated hydroxylamine-oxidizing enzyme kustc1061 (KsHOX) from K. stuttgartiensis. Interestingly, the HDH trimers formed octamers in solution, each octamer harbouring an amazing 192 c-type heme moieties. While HAO and KsHOX are capable of hydrazine oxidation as well, KsHDH was highly specific for this activity. To understand this specificity, we performed detailed amino acid sequence analyses and investigated the catalytic and spectroscopic (electronic absorbance, EPR) properties of KsHDH in comparison with the well-defined HAO and HOX. We conclude that HDH specificity is most likely derived from structural changes around the catalytic heme 4 (“P460”) and of the electron-wiring circuit comprising seven His/His-ligated c-type hemes in each subunit. These nuances make HDH a globally prominent N2-producing enzyme, next to nitrous oxide (N2O) reductase from denitrifying microorganisms.

Details

Original languageEnglish
Pages (from-to)17077-17092
JournalJournal of Biological Chemistry
Volume291
Issue number33
Early online date17 Jun 2016
DOIs
Publication statusPublished - 12 Aug 2016
Peer-reviewedYes

Keywords

    Research areas

  • electron paramagnetic resonance (EPR), enzyme kinetics, enzyme purification, nitrogen metabolism, reactive nitrogen species (RNS), Anaerobic Ammonium Oxidation, hydrazine, octaheme proteins

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