Quercetin 2,4‐Dioxygenase Activates Dioxygen in a Side‐On O2–Ni Complex |
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Authors: | Dr Jae‐Hun Jeoung Dr Dimitrios Nianios Prof?Dr Susanne Fetzner Prof?Dr Holger Dobbek |
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Institution: | 1. Institut für Biologie, Strukturbiologie/Biochemie, Humboldt-Universit?t zu Berlin, Berlin, Germany;2. Institut für Molekulare Mikrobiologie und Biotechnologie, Westf?lische Wilhelms-Universit?t Münster, Münster, Germany |
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Abstract: | 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 Ni2+ ion. The Ni2+ ion is coordinated by three histidine residues and a glutamate residue (E76) in all three states. Upon binding, quercetin replaces one water ligand at Ni and is stabilized by a short hydrogen bond through E76, the carboxylate group of which rotates by 90°. 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 Ni2+ ion and is perpendicular to the C2?C3 and C3?C4 bonds of quercetin, which are cleaved in the following reaction steps. |
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Keywords: | biocatalysis carbon monoxide dioxygen activation dioxygenases nickel superoxo complexes |
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