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Hexbyte Glen Cove The chemistry lab inside cells

Hexbyte Glen Cove

(A) X-ray crystal structure of QhpG and schematic of crosslinked QhpC. The substrate QhpC is bound to the pocket formed by the catalytic domain, which includes the FAD cofactor and the small domain. (B) QhpG-catalyzed dihydroxylation reaction. Credit: Osaka University

Investigators from the Institute of Scientific and Industrial Research at Osaka University, together with Hiroshima Institute of Technology, have announced the discovery of a new protein that allows an organism to conduct an initial and essential step in converting amino acid residues on a crosslinked polypeptide into an enzyme cofactor. This research may lead to a better understanding of the biochemistry underlying catalysis in cells.

Every living cell is constantly pulsing with an array of biochemical reactions. The rates of these reactions are controlled by special proteins called enzymes, which catalyze specific processes that would otherwise take much longer. A number of enzymes require specialized molecules called “cofactors,” which can help shuttle electrons back and forth during oxidation-reduction reactions. But these cofactors themselves must be produced by the organisms, and often require the assistance of previously existing proteins.

Now, a team of scientists at Osaka University has identified a novel protein called QhpG that is essential for the biogenesis of the cofactor cysteine tryptophylquinone (CTQ). By analyzing the mass of the reaction products and determining its , they were able to deduce the catalytic function of QhpG, which is adding two to a specific tryptophan residue within an active-site subunit QhpC of quinoheme protein amine dehydrogenase, the bacterial enzyme catalyzing the oxidation of various primary amines. The resulting dihydroxylated tryptophan and an adjacent cysteine residue are finally converted to cofactor CTQ.

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