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Publication Abstract from PubMed

Quercetin 2,4-dioxygenase (quercetinase) from Streptomyces uses nickel as the active-site cofactor to catalyze oxidative cleavage of the flavonol quercetin. How this unusual active-site metal supports catalysis and O2 activation is under debate. We present crystal structures of Ni-quercetinase in three different states, thus providing direct insight into how quercetin and O2 are activated at the Ni(2+) ion. The Ni(2+) ion is coordinated by three histidine residues and a glutamate residue (E(76) ) in all three states. Upon binding, quercetin replaces one water ligand at Ni and is stabilized by a short hydrogen bond through E(76) , the carboxylate group of which rotates by 90 degrees . This conformational change weakens the interaction between Ni and the remaining water ligand, thereby preparing a coordination site at Ni to bind O2 . O2 binds side-on to the Ni(2+) ion and is perpendicular to the C2-C3 and C3-C4 bonds of quercetin, which are cleaved in the following reaction steps.

Quercetin 2,4-Dioxygenase Activates Dioxygen in a Side-On O2 -Ni Complex.,Jeoung JH, Nianios D, Fetzner S, Dobbek H Angew Chem Int Ed Engl. 2016 Mar 1;55(10):3281-4. doi: 10.1002/anie.201510741., Epub 2016 Feb 5. PMID:26846734^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.