title: Elucidation of the Fe(IV)=O intermediate in the catalytic cycle of the halogenase SyrB2.
abstract: Mononuclear non-haem iron (NHFe) enzymes catalyse a broad range of oxidative reactions, including halogenation, hydroxylation, ring closure, desaturation and aromatic ring cleavage reactions. They are involved in a number of biological processes, including phenylalanine metabolism, the production of neurotransmitters, the hypoxic response and the biosynthesis of secondary metabolites. The reactive intermediate in the catalytic cycles of these enzymes is a high-spin S = 2 Fe(IV)=O species, which has been trapped for a number of NHFe enzymes, including the halogenase SyrB2 (syringomycin biosynthesis enzyme 2). Computational studies aimed at understanding the reactivity of this Fe(IV)=O intermediate are limited in applicability owing to the paucity of experimental knowledge about its geometric and electronic structure. Synchrotron-based nuclear resonance vibrational spectroscopy (NRVS) is a sensitive and effective method that defines the dependence of the vibrational modes involving Fe on the nature of the Fe(IV)=O active site. Here we present NRVS structural characterization of the reactive Fe(IV)=O intermediate of a NHFe enzyme, namely the halogenase SyrB2 from the bacterium Pseudomonas syringae pv. syringae. This intermediate reacts via an initial hydrogen-atom abstraction step, performing subsequent halogenation of the native substrate or hydroxylation of non-native substrates. A correlation of the experimental NRVS data to electronic structure calculations indicates that the substrate directs the orientation of the Fe(IV)=O intermediate, presenting specific frontier molecular orbitals that can activate either selective halogenation or hydroxylation.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Shaun D
authors.initials: SD
authors.lastname: Wong
authors.forename: Martin
authors.initials: M
authors.lastname: Srnec
authors.forename: Megan L
authors.initials: ML
authors.lastname: Matthews
authors.forename: Lei V
authors.initials: LV
authors.lastname: Liu
authors.forename: Yeonju
authors.initials: Y
authors.lastname: Kwak
authors.forename: Kiyoung
authors.initials: K
authors.lastname: Park
authors.forename: Caleb B
authors.initials: CB
authors.lastname: Bell
authors.forename: E Ercan
authors.initials: EE
authors.lastname: Alp
authors.forename: Jiyong
authors.initials: J
authors.lastname: Zhao
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Yoda
authors.forename: Shinji
authors.initials: S
authors.lastname: Kitao
authors.forename: Makoto
authors.initials: M
authors.lastname: Seto
authors.forename: Carsten
authors.initials: C
authors.lastname: Krebs
authors.forename: J Martin
authors.initials: JM
authors.lastname: Bollinger
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D055162:Biocatalysis; D054879:Halogenation; D006900:Hydroxylation; D007501:Iron / Q000737:chemistry*; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D044224:Pseudomonas syringae / Q000201:enzymology
chemical_list: C066317:ferryl iron; D007501:Iron; D010088:Oxidoreductases