1h1m: Difference between revisions

Quercetin 2,3-dioxygenase (2,3QD) is the only firmly established copper, dioxygenase known so far. Depending solely on a mononuclear Cu center, it, catalyzes the breakage of the O-heterocycle of flavonols, producing more, easily degradable phenolic carboxylic acid ester derivatives. In the, enzymatic process, two CC bonds are broken and concomitantly carbon, monoxide is released. The x-ray structures of Aspergillus japonicus 2,3QD, anaerobically complexed with the substrate kaempferol and the natural, substrate quercetin have been determined at 1.90- and 1.75-A resolution, respectively. Flavonols coordinate to the copper ion as monodentate, ligands through their 3OH group. They occupy a shallow and overall, hydrophobic cavity proximal to the metal center. As a result of a van der, Waals contact between the most outward flavonol A-ring and Pro(164), a, flexible loop in front of the active site becomes partly ordered., Interestingly, flavonols bound to 2,3QD are bent at the C2 atom, which is, pyramidalized. The increased local sp(3) character at this atom may, stabilize a carbon-centered radical activated for dioxygen attack. Glu(73), coordinates the copper through its O epsilon 1 atom. The short distance of, about 2.55 A between its O epsilon 2 atom and the flavonol O3 atom, suggests that a hydrogen bond exists between the two atoms, indicating, that Glu(73) can act as a base in flavonol deprotonation and that it, retains the proton. Structure-based geometric considerations indicate O(2), binding to the flavonol C2 atom as the preferred route for flavonol, dioxygenation.

1H1M is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Aspergillus_japonicus Aspergillus japonicus] with NAG, CU, KMP and MPD as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Quercetin_2,3-dioxygenase Quercetin 2,3-dioxygenase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.13.11.24 1.13.11.24] Structure known Active Site: CUA. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1H1M OCA].  

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