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Substrate-Binding Mechanism of a TypeⅠ Extradiol Dioxygenase

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Substrate-Binding Mechanism of a TypeⅠ Extradiol Dioxygenase
Other Titles
TypeⅠ Extradiol Dioxygenase의 기질결합 기작
Kim, Kyungsun
Kyung Jin Kim
Ha Yeon Cho
Kim, Dockyu
Kim, Eungbin
Kang, Beom Sik
Seo Yean Sohn
Hyo Je Cho
Extradiol dioxygenase; Rhodococcus; Substrate-binding
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Kim, Kyungsun, et al. 2010. Substrate-Binding Mechanism of a TypeⅠ Extradiol Dioxygenase. 한국미생물학회연합. 한국미생물학회연합. 2010.10.14~.
A meta-cleavage pathway for the aerobic degradation of aromatic hydrocarbons is catalyzed by extradiol dioxygenases via a two-step mechanism: catechol substrate binding and dioxygen incorporation. The binding of substrate triggers the release of water, thereby opening a coordination site for molecular oxygen. The crystal structures of Selenomethionine-substituted AkbC, a type I extradiol dioxygenase, and the enzyme-substrate (3-methylcatechol) complex revealed the substrate-binding process of extradiol dioxygenase. AkbC was found to be composed of eight identical subunits, each containing one ferrous ion. AkbC is composed of an N-domain (residues M1-G138) and an active C-domain (K139-G284), which contains iron coordinated by a 2-His-1-carboxylate facial triad motif (H149, H212, and E263). The C-domain includes a β-hairpin structure (β11-β12) and a C-terminal tail (H285-G300). In substrate-bound AkbC, 3-methylcatechol interacts with the iron via a single hydroxyl group, which represents an intermediate stage in the substrate-binding process. Structure-based mutagenesis combined with structural analyses reveals that the C-terminal tail and β-hairpin form part of the substrate-binding pocket that is responsible for substrate specificity by blocking substrate entry. Once a substrate enters the active site, these structural elements also play a role in the correct positioning of the substrate. Based on the results presented here, a putative substrate-binding mechanism is proposed.
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