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Evolution des mécanismes d'accumulation et de transport de l'iode dans les organismes marins: étude de la structure/fonction de protéines du métabolisme iodé chez la bactérie Zobellia galactanivorans.

Abstract : In marine environment, biogenic emissions of iodinated compounds play an essential role in iodidne biogeochemical cycle. Nevertheless, enzymatic processes involved in iodine absorption and storage or in the synthesis of iodinated compounds are poorly known in marine organisms, especially in bacteria. Several genes, potentially involved in iodine metabolism, have been identified in the genome of a marine bacterium, Zobellia galactanivorans. One of these genes codes for a vanadium iodoperoxidase (VIPO), an enzyme specific of iodide oxidation. The main part of the thesis project was to understand molecular mechanisms controlling the specificity of vanadium haloperoxidase (VHPO) for some halides, by studying the VIPO from Z. galactanivorans by directed mutagenesis and structural biology. To fullfill this project, twelve mutated enzymes were produced and characterized at a biochemical level. For some of them, mutations lead to a loss of activity, a modification of their catalytic properties or a slight VBPO activity. The wild type and three mutated enzymes were also analyzed by X ray absorption and diffraction spectroscopy in order to link the structural modifications to their catalytic properties. The results of this study suggest that the main factor modulating the specificity in these enzymes is a modification of the peroxovanadate redox potential. Biochemical analyses were performed on two other proteins identified in the genome of Z. galactanivorans. The first protein was characterized as a new VIPO. For the second protein, similar to mammal iodotyrosine deiodinase, the biochemical activity remains to be characterized. Z. galactanivorans seems to have several enzymes that oxidize iodide or split C-I bond. In parallel with this work, the localization and speciation of iodine were analyzed by chemical imaging in Z. galactanivorans and in the kelp L. digitata, known to highly concentrate iodide. All this information allow a better understanding on the molecular mechanisms involved in the specificity for halide in VHPO and on the bacterial origin of these proteins. More generally, these studies assess to understand the role of iodine metabolism in some marine bacteria and their role in the biogeochemical cycle of this element.
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https://tel.archives-ouvertes.fr/tel-00959056
Contributor : Jean-Baptiste Fournier <>
Submitted on : Thursday, March 13, 2014 - 5:20:22 PM
Last modification on : Thursday, March 12, 2020 - 4:50:03 PM
Document(s) archivé(s) le : Friday, June 13, 2014 - 12:20:57 PM

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  • HAL Id : tel-00959056, version 1

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Jean-Baptiste Fournier. Evolution des mécanismes d'accumulation et de transport de l'iode dans les organismes marins: étude de la structure/fonction de protéines du métabolisme iodé chez la bactérie Zobellia galactanivorans.. Biologie structurale [q-bio.BM]. Université Pierre et Marie Curie - Paris VI, 2014. Français. ⟨tel-00959056v1⟩

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