title: X-ray structure determination of a vanadium-dependent haloperoxidase from Ascophyllum nodosum at 2.0 A resolution.
abstract: The homo-dimeric structure of a vanadium-dependent haloperoxidase (V-BPO) from the brown alga Ascophyllum nodosum (EC 1.1.11.X) has been solved by single isomorphous replacement anomalous scattering (SIRAS) X-ray crystallography at 2.0 A resolution (PDB accession code 1QI9), using two heavy-atom datasets of a tungstate derivative measured at two different wavelengths. The protein sequence (SwissProt entry code P81701) of V-BPO was established by combining results from protein and DNA sequencing, and electron density interpretation. The enzyme has nearly an all-helical structure, with two four-helix bundles and only three small beta-sheets. The holoenzyme contains trigonal-bipyramidal coordinated vanadium atoms at its two active centres. Structural similarity to the only other structurally characterized vanadium-dependent chloroperoxidase (V-CPO) from Curvularia inaequalis exists in the vicinity of the active site and to a lesser extent in the central four-helix bundle. Despite the low sequence and structural similarity between V-BPO and V-CPO, the vanadium binding centres are highly conserved on the N-terminal side of an alpha-helix and include the proposed catalytic histidine residue (His418(V-BPO)/His404(V-CPO)). The V-BPO structure contains, in addition, a second histidine near the active site (His411(V-BPO)), which can alter the redox potential of the catalytically active VO2-O2 species by protonation/deprotonation reactions. Specific binding sites for the organic substrates, like indoles and monochlordimedone, or for halide ions are not visible in the V-BPO structure. A reaction mechanism for the enzymatic oxidation of halides is discussed, based on the present structural, spectroscopic and biochemical knowledge of vanadium-dependent haloperoxidases, explaining the observed enzymatic differences between both enzymes.
authors.affiliation: Department of Molecular Structure Research, GBF (Gesellschaft für Biotechnologische Forschung), Mascheroder Weg 1, Braunschweig, D-38124, Germany. michael-wayand@mpi-dortmund.mpg.de
authors.forename: M
authors.initials: M
authors.lastname: Weyand
authors.forename: H
authors.initials: H
authors.lastname: Hecht
authors.forename: M
authors.initials: M
authors.lastname: Kiess
authors.forename: M
authors.initials: M
authors.lastname: Liaud
authors.forename: H
authors.initials: H
authors.lastname: Vilter
authors.forename: D
authors.initials: D
authors.lastname: Schomburg
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000201:enzymology; D001665:Binding Sites; D002711:Chloride Peroxidase / Q000737:chemistry / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D004220:Disulfides; D006219:Halogens / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000737:chemistry* / Q000145:classification / Q000378:metabolism*; D000459:Phaeophyceae / Q000201:enzymology*; D017433:Protein Structure, Secondary; D011522:Protons; D016415:Sequence Alignment; D014638:Vanadates / Q000378:metabolism*
chemical_list: D004220:Disulfides; D006219:Halogens; D011522:Protons; D014638:Vanadates; D006639:Histidine; D010544:Peroxidases; C026195:bromide peroxidase; D002711:Chloride Peroxidase