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To be or not to be?? The dilemma of an enzyme’s Life…

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José Artur Brito, Membrane Protein Crystallography

When 02 Jul, 2008 from
12:00 pm to 01:00 pm
Where Auditorium
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The biological involvement in the dissimilatory oxidation of inorganic sulphur compounds to elemental sulphur (So) has been established for more than a century. Inorganic sulphur compounds can serve as electron donors or acceptors in many phototrophic and chemotrophic prokaryotes, mostly with sulphate as the final oxidation product of this energy-yielding process.  Besides the importance of these pathways for the global biogeochemical cycles in earth, the metabolism of hydrogen sulphide has received a renewed interest, due to its proposed role as an eukaryotic signal molecule as well as in microbial pathogenicity.
We solved the first X-ray structure of a sulphide:quinone oxidoreductase (SQR) isolated from the hyperthermoacidophilic archaeon Acidianus ambivalens, to 2.67 Ǻ resolution. This enzyme was initially characterized as a type 2 NADH:quinone oxidoreductase but X-ray crystallography studies showed that this activity was only due to an unspecific reaction between the substrate and the enzyme’s cofactor. We will present the native and ascorbate-reduced enzyme’s structures and discuss a possible mechanism for sulphide oxidation and a new putative pathway of sulphur oxidation coupled to oxygen reduction.
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