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A low-potential terminal oxidase associated with the iron-only nitrogenase from the nitrogen-fixing bacterium Azotobacter vinelandii

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Title: A low-potential terminal oxidase associated with the iron-only nitrogenase from the nitrogen-fixing bacterium Azotobacter vinelandii
Authors: Varghese, F
Kabasakal, BV
Cotton, CA
Schumacher, J
Rutherford, AW
Fantuzzi, A
Murray, JW
Item Type: Journal Article
Abstract: The biological route for nitrogen gas entering the biosphere is reduction to ammonia by the nitrogenase enzyme, which is inactivated by oxygen. Three types of nitrogenase exist, the least studied of which is the iron-only nitrogenase. The Anf3 protein in the bacterium Rhodobacter capsulatus is essential for diazotrophic (i.e. nitrogen-fixing) growth with the iron-only nitrogenase, but its enzymatic activity and function are unknown. Here, we biochemically and structurally characterize Anf3 from the model diazotrophic bacterium Azotobacter vinelandii. Determining the Anf3 crystal structure to atomic resolution, we observed that it is a dimeric flavocytochrome with an unusually close interaction between the heme and the flavin adenine dinucleotide cofactors. Measuring the reduction potentials by spectroelectrochemical redox titration, we observed values of -420 ± 10 mV and -330 ± 10 mV for the two FAD potentials and -340 ± 1 mV for the heme. We further show that Anf3 accepts electrons from spinach ferredoxin and that Anf3 consumes oxygen without generating superoxide or hydrogen peroxide. We predict that Anf3 protects the iron-only nitrogenase from oxygen inactivation by functioning as an oxidase in respiratory protection, with flavodoxin or ferredoxin as the physiological electron donors.
Issue Date: 1-May-2019
Date of Acceptance: 1-May-2019
URI: http://hdl.handle.net/10044/1/70417
DOI: https://dx.doi.org/10.1074/jbc.RA118.007285
ISSN: 0021-9258
Publisher: American Society for Biochemistry and Molecular Biology
Journal / Book Title: Journal of Biological Chemistry
Copyright Statement: © 2019 The Author(s). Published under license by The American Society for Biochemistry and Molecular Biology, Inc.
Sponsor/Funder: Biotechnology and Biological Sciences Research Council (BBSRC)
Funder's Grant Number: BB/L011468/1
Keywords: dioxygenase
enzyme structure
nitrogen fixation
nitrogenase
oxidase
dioxygenase
enzyme structure
nitrogen fixation
nitrogenase
oxidase
06 Biological Sciences
11 Medical and Health Sciences
03 Chemical Sciences
Biochemistry & Molecular Biology
Publication Status: Published online
Conference Place: United States
Online Publication Date: 2019-05-01
Appears in Collections:Faculty of Natural Sciences



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