Evolution moléculaire de la fonction de liaison du sulfure d'hydrogène par les hémoglobines de Riftia pachyptila, annélide tubicole des sources hydrothermales profondes

Abstract : The hexagonal-bilayer hemoglobin of the vestimentifera Riftia pachyptila, a tube-worm living close to hydrothermal vents on the East Pacific Ridge, have the capacity to simultaneously bind and transport hydrogen sulfide (H2S) and oxygen (O2) from the tube worm gills to its endosymbiotic sulfo-oxidising bacteria. These bacteria synthesize from H2S, CO2 and O2 some organic compounds they provide to their host. In order to understand how the sulfide binding function has appeared and has been maintained, we cloned and sequenced the Riftia pachyptila hemoglobin multigenic family. Molecular evolution studies show that paralogous globin genes in this family have different evolutionary rates. Two globins strains are involved in H2S binding, and use for that free cysteine residues. These two globin strains exhibit slower evolutionary rates (strong selection pressure) than globin strains solely involved in oxygen transport. Free cysteines molecular environment is strongly conserved in orthologous globins from both annelid species binding hydrogen sulfide or not. Synonymous and not-synonymous analysis between orthologous globins revealed that the site occupied by the free cysteine residue in annelids living in sulfide-rich environments and occupied by other amino acids in annelids from sulfide-free environment, has undergone positive selection in species from sulfide-free environment. From these results and the selective constrains (H2S occurrence) found in intertidal, hydrothermal and terrestrial environments, we proposed a scenario suggesting that H2S binging via a free cysteine residue has been lost in modern annelids living in free-sulfide environments (constraint relaxation followed by positive selection). Our work suggests that this adaptation to sulfide-rich environments is a plesiomorphic feature, and that the annelids ancestor could have live in a sulfide-rich environment.
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  • HAL Id : tel-01112979, version 1

Citation

Xavier Bailly. Evolution moléculaire de la fonction de liaison du sulfure d'hydrogène par les hémoglobines de Riftia pachyptila, annélide tubicole des sources hydrothermales profondes. Biologie moléculaire. Paris 6, 2003. Français. ⟨tel-01112979⟩

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