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Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin

The substrates O(2) and NO cooperatively activate the NO dioxygenase function of Escherichia coli flavohemoglobin. Steady-state and transient kinetic measurements support a structure-based mechanistic model in which O(2) and NO movements and conserved amino acids at the E11, G8, E2, E7, B10, and F7...

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Autores principales: Gardner, Anne M., Gardner, Paul R.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Society for Biochemistry and Molecular Biology 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7948479/
https://www.ncbi.nlm.nih.gov/pubmed/33310705
http://dx.doi.org/10.1074/jbc.RA120.016637
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author Gardner, Anne M.
Gardner, Paul R.
author_facet Gardner, Anne M.
Gardner, Paul R.
author_sort Gardner, Anne M.
collection PubMed
description The substrates O(2) and NO cooperatively activate the NO dioxygenase function of Escherichia coli flavohemoglobin. Steady-state and transient kinetic measurements support a structure-based mechanistic model in which O(2) and NO movements and conserved amino acids at the E11, G8, E2, E7, B10, and F7 positions within the globin domain control activation. In the cooperative and allosteric mechanism, O(2) migrates to the catalytic heme site via a long hydrophobic tunnel and displaces LeuE11 away from the ferric iron, which forces open a short tunnel to the catalytic site gated by the ValG8/IleE15 pair and LeuE11. NO permeates this tunnel and leverages upon the gating side chains triggering the CD loop to furl, which moves the E and F-helices and switches an electron transfer gate formed by LysF7, GlnE7, and water. This allows FADH(2) to reduce the ferric iron, which forms the stable ferric–superoxide–TyrB10/GlnE7 complex. This complex reacts with internalized NO with a bimolecular rate constant of 10(10) M(−1) s(−1) forming nitrate, which migrates to the CD loop and unfurls the spring-like structure. To restart the cycle, LeuE11 toggles back to the ferric iron. Actuating electron transfer with O(2) and NO movements averts irreversible NO poisoning and reductive inactivation of the enzyme. Together, structure snapshots and kinetic constants provide glimpses of intermediate conformational states, time scales for motion, and associated energies.
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spelling pubmed-79484792021-03-19 Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin Gardner, Anne M. Gardner, Paul R. J Biol Chem Research Article The substrates O(2) and NO cooperatively activate the NO dioxygenase function of Escherichia coli flavohemoglobin. Steady-state and transient kinetic measurements support a structure-based mechanistic model in which O(2) and NO movements and conserved amino acids at the E11, G8, E2, E7, B10, and F7 positions within the globin domain control activation. In the cooperative and allosteric mechanism, O(2) migrates to the catalytic heme site via a long hydrophobic tunnel and displaces LeuE11 away from the ferric iron, which forces open a short tunnel to the catalytic site gated by the ValG8/IleE15 pair and LeuE11. NO permeates this tunnel and leverages upon the gating side chains triggering the CD loop to furl, which moves the E and F-helices and switches an electron transfer gate formed by LysF7, GlnE7, and water. This allows FADH(2) to reduce the ferric iron, which forms the stable ferric–superoxide–TyrB10/GlnE7 complex. This complex reacts with internalized NO with a bimolecular rate constant of 10(10) M(−1) s(−1) forming nitrate, which migrates to the CD loop and unfurls the spring-like structure. To restart the cycle, LeuE11 toggles back to the ferric iron. Actuating electron transfer with O(2) and NO movements averts irreversible NO poisoning and reductive inactivation of the enzyme. Together, structure snapshots and kinetic constants provide glimpses of intermediate conformational states, time scales for motion, and associated energies. American Society for Biochemistry and Molecular Biology 2020-12-17 /pmc/articles/PMC7948479/ /pubmed/33310705 http://dx.doi.org/10.1074/jbc.RA120.016637 Text en © 2020 The Authors https://creativecommons.org/licenses/by/4.0/This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Research Article
Gardner, Anne M.
Gardner, Paul R.
Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
title Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
title_full Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
title_fullStr Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
title_full_unstemmed Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
title_short Allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
title_sort allostery in the nitric oxide dioxygenase mechanism of flavohemoglobin
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7948479/
https://www.ncbi.nlm.nih.gov/pubmed/33310705
http://dx.doi.org/10.1074/jbc.RA120.016637
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