title: Direct visualization of a Fe(IV)-OH intermediate in a heme enzyme.
abstract: Catalytic heme enzymes carry out a wide range of oxidations in biology. They have in common a mechanism that requires formation of highly oxidized ferryl intermediates. It is these ferryl intermediates that provide the catalytic engine to drive the biological activity. Unravelling the nature of the ferryl species is of fundamental and widespread importance. The essential question is whether the ferryl is best described as a Fe(IV)=O or a Fe(IV)-OH species, but previous spectroscopic and X-ray crystallographic studies have not been able to unambiguously differentiate between the two species. Here we use a different approach. We report a neutron crystal structure of the ferryl intermediate in Compound II of a heme peroxidase; the structure allows the protonation states of the ferryl heme to be directly observed. This, together with pre-steady state kinetic analyses, electron paramagnetic resonance spectroscopy and single crystal X-ray fluorescence, identifies a Fe(IV)-OH species as the reactive intermediate. The structure establishes a precedent for the formation of Fe(IV)-OH in a peroxidase.
authors.affiliation: Department of Molecular and Cell Biology and Leicester Institute of Structural and Chemical Biology, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK.
authors.forename: Hanna
authors.identifier: http://orcid.org/0000-0001-6941-4808
authors.initials: H
authors.lastname: Kwon
authors.affiliation: Department of Molecular and Cell Biology and Leicester Institute of Structural and Chemical Biology, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK.
authors.forename: Jaswir
authors.initials: J
authors.lastname: Basran
authors.affiliation: Department of Molecular and Cell Biology and Leicester Institute of Structural and Chemical Biology, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK.|Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Cecilia M
authors.initials: CM
authors.lastname: Casadei
authors.affiliation: The Photon Science Institute and School of Chemistry, The University of Manchester, Manchester M13 9PL, UK.
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: Fielding
authors.affiliation: Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstr. 1, 85748 Garching, Germany.
authors.forename: Tobias E
authors.initials: TE
authors.lastname: Schrader
authors.affiliation: Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstr. 1, D-85748 Garching, Germany.
authors.forename: Andreas
authors.identifier: http://orcid.org/0000-0002-1477-5590
authors.initials: A
authors.lastname: Ostermann
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Juliette M
authors.initials: JM
authors.lastname: Devos
authors.affiliation: Diamond Light Source Ltd, Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK.
authors.forename: Pierre
authors.initials: P
authors.lastname: Aller
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Matthew P
authors.identifier: http://orcid.org/0000-0002-6412-4358
authors.initials: MP
authors.lastname: Blakeley
authors.affiliation: Department of Molecular and Cell Biology and Leicester Institute of Structural and Chemical Biology, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK.
authors.forename: Peter C E
authors.identifier: http://orcid.org/0000-0003-1762-9238
authors.initials: PCE
authors.lastname: Moody
authors.affiliation: Department of Chemistry and Leicester Institute of Structural and Chemical Biology, University of Leicester, University Road, Leicester LE1 9HN, UK.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Raven
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D033363:Neutron Diffraction; D010544:Peroxidases / Q000378:metabolism*
chemical_list: D006418:Heme; D003577:Cytochrome P-450 Enzyme System; D007501:Iron; D010544:Peroxidases