title: Structural basis of biological NO generation by octaheme oxidoreductases.
abstract: Nitric oxide is an important molecule in all domains of life with significant biological functions in both pro- and eukaryotes. Anaerobic ammonium-oxidizing (anammox) bacteria that contribute substantially to the release of fixed nitrogen into the atmosphere use the oxidizing power of NO to activate inert ammonium into hydrazine (N2H4). Here, we describe an enzyme from the anammox bacterium Kuenenia stuttgartiensis that uses a novel pathway to make NO from hydroxylamine. This new enzyme is related to octaheme hydroxylamine oxidoreductase, a key protein in aerobic ammonium-oxidizing bacteria. By a multiphasic approach including the determination of the crystal structure of the K. stuttgartiensis enzyme at 1.8 Å resolution and refinement and reassessment of the hydroxylamine oxidoreductase structure from Nitrosomonas europaea, both in the presence and absence of their substrates, we propose a model for NO formation by the K. stuttgartiensis enzyme. Our results expand the understanding of the functions that the widespread family of octaheme proteins have.
authors.affiliation: From the Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, 6525AJ Nijmegen, The Netherlands.
authors.forename: Wouter J
authors.initials: WJ
authors.lastname: Maalcke
authors.forename: Andreas
authors.initials: A
authors.lastname: Dietl
authors.forename: Sophie J
authors.initials: SJ
authors.lastname: Marritt
authors.forename: Julea N
authors.initials: JN
authors.lastname: Butt
authors.forename: Mike S M
authors.initials: MS
authors.lastname: Jetten
authors.forename: Jan T
authors.initials: JT
authors.lastname: Keltjens
authors.forename: Thomas R M
authors.initials: TR
authors.lastname: Barends
authors.forename: Boran
authors.initials: B
authors.lastname: Kartal
mesh_terms: D000641:Ammonia / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006834:Hydrazines / Q000737:chemistry / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D061328:Planctomycetales / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D006834:Hydrazines; C029424:hydrazine; D009569:Nitric Oxide; D000641:Ammonia; D010088:Oxidoreductases
keywords: Anaerobic Ammonium Oxidation; Enzyme Kinetics; Enzyme Purification; Hydroxylamine; Nitric Oxide; Nitrogen Metabolism; Octaheme Proteins; Protein Structure; Reactive Nitrogen Species; X-ray Crystallography