title: Vanadium-dependent iodoperoxidases in Laminaria digitata, a novel biochemical function diverging from brown algal bromoperoxidases.
abstract: The brown alga Laminaria digitata features a distinct vanadium-dependent iodoperoxidase (vIPO) activity, which has been purified to electrophoretic homogeneity. Steady-state analyses at pH 6.2 are reported for vIPO (K (m) (I-) = 2.5 mM; k (cat) (I-) = 462 s(-1)) and for the previously characterised vanadium-dependent bromoperoxidase in L. digitata (K (m) (I-) =18.1 mM; k (cat) (I-) = 38 s(-1)). Although the vIPO enzyme specifically oxidises iodide, competition experiments with halides indicate that bromide is a competitive inhibitor with respect to the fixation of iodide. A full-length complementary ANA (cDNA) was cloned and shown to be actively transcribed in L. digitata and to encode the vIPO enzyme. Mass spectrometry analyses of tryptic digests of vIPO indicated the presence of at least two very similar proteins, in agreement with Southern analyses showing that vIPOs are encoded by a multigenic family in L. digitata. Phylogenetic analyses indicated that vIPO shares a close common ancestor with brown algal vanadium-dependent bromoperoxidases. Based on a three-dimensional structure model of the vIPO active site and on comparisons with those of other vanadium-dependent haloperoxidases, we propose a hypothesis to explain the evolution of strict specificity for iodide in L. digitata vIPO.
authors.affiliation: Station Biologique, UMR 7139 CNRS, Goëmar-Université Pierre & Marie Curie, Roscoff Cedex, France. potin@sb-roscoff.fr
authors.forename: Carole
authors.initials: C
authors.lastname: Colin
authors.forename: Catherine
authors.initials: C
authors.lastname: Leblanc
authors.forename: Gurvan
authors.initials: G
authors.lastname: Michel
authors.forename: Elsa
authors.initials: E
authors.lastname: Wagner
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Leize-Wagner
authors.forename: Alain
authors.initials: A
authors.lastname: Van Dorsselaer
authors.forename: Philippe
authors.initials: P
authors.lastname: Potin
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D019143:Evolution, Molecular; D007453:Iodide Peroxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D007795:Laminaria / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism*; D010802:Phylogeny; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D010544:Peroxidases; C026195:bromide peroxidase; C414928:vanadium iodoperoxidase; D007453:Iodide Peroxidase