title: Reductive dehalogenase structure suggests a mechanism for B12-dependent dehalogenation.
abstract: Organohalide chemistry underpins many industrial and agricultural processes, and a large proportion of environmental pollutants are organohalides. Nevertheless, organohalide chemistry is not exclusively of anthropogenic origin, with natural abiotic and biological processes contributing to the global halide cycle. Reductive dehalogenases are responsible for biological dehalogenation in organohalide respiring bacteria, with substrates including polychlorinated biphenyls or dioxins. Reductive dehalogenases form a distinct subfamily of cobalamin (B12)-dependent enzymes that are usually membrane associated and oxygen sensitive, hindering detailed studies. Here we report the characterization of a soluble, oxygen-tolerant reductive dehalogenase and, by combining structure determination with EPR (electron paramagnetic resonance) spectroscopy and simulation, show that a direct interaction between the cobalamin cobalt and the substrate halogen underpins catalysis. In contrast to the carbon-cobalt bond chemistry catalysed by the other cobalamin-dependent subfamilies, we propose that reductive dehalogenases achieve reduction of the organohalide substrate via halogen-cobalt bond formation. This presents a new model in both organohalide and cobalamin (bio)chemistry that will guide future exploitation of these enzymes in bioremediation or biocatalysis.
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Karl Ap
authors.initials: KA
authors.lastname: Payne
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Carolina P
authors.initials: CP
authors.lastname: Quezada
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Karl
authors.initials: K
authors.lastname: Fisher
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Dunstan
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Fraser A
authors.initials: FA
authors.lastname: Collins
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Hanno
authors.initials: H
authors.lastname: Sjuts
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Levy
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Sam
authors.initials: S
authors.lastname: Hay
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: Stephen Ej
authors.initials: SE
authors.lastname: Rigby
authors.affiliation: Manchester Institute for Biotechnology, University of Manchester, Princess Street 131 M1 7DN Manchester, UK.
authors.forename: David
authors.initials: D
authors.lastname: Leys
mesh_terms: D055162:Biocatalysis; D003035:Cobalt / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D054879:Halogenation; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D059127:Phyllobacteriaceae / Q000201:enzymology*; D011487:Protein Conformation; D012995:Solubility; D014805:Vitamin B 12 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010636:Phenols; C038964:2,6-dibromophenol; D003035:Cobalt; D010088:Oxidoreductases; D014805:Vitamin B 12; D010100:Oxygen