Spectroscopic and electronic structure studies of the role of active site interactions in the decarboxylation reaction of α-keto acid-dependent dioxygenases
Spectroscopic and electronic structure studies of the role of active site interactions in the decarboxylation reaction of α-keto acid-dependent dioxygenases
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DOI：
10.1016/j.jinorgbio.2006.08.021
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发表时间：
2006-12-01
影响因子：
3.9
通讯作者：
Solomon, Edward I.
中科院分区：
文献类型：
--
作者：
Neidig, Michael L.;Brown, Christina D.;Solomon, Edward I.
α-酮戊二酸（α-KG）依赖性双加氧酶是一类大的单核非血红素铁酶，其需要Fe-II、α-KG和双氧进行催化，其中α-KG共底物提供双氧活化所需的两个额外电子。这些酶的一个亚类存在，其中α-酮酸与底物共价连接，包括（4-羟基）扁桃酸合酶（HmaS）和（4-羟基苯基）丙酮酸双加氧酶（HPPD），它们利用相同的底物，但表现出两种不同的一般反应性（H-原子夺取和亲电子攻击）。阿维链霉菌HPPD的先前动力学研究表明，底物类似物苯丙酮酸（PPA），其与正常底物（4-羟基苯基）丙酮酸（HPP）的区别仅在于芳环上不存在对羟基，不诱导与分子氧的反应。虽然Fe-IV=O中间体被认为是将底物转化为产物的反应性物质，但利用O-2产生这种物质的关键步骤是α-酮酸的脱羧。人们普遍认为，脱羧的两个要求是α-酮酸与Felt的二齿配位以及存在用于O-2反应的5C Fe-II位点。圆二色性和磁性圆二色性的研究表明，这两种酶与PPA的复合物是类似的双齿的a-KG协调和5C Fe-II网站。然而，动力学研究表明，虽然HmaS与PPA以类似于与HPP的反应的偶联反应反应进行反应，但HPPD与PPA以与HPP的反应相比类似于10（5）倍降低的速率进行非偶联反应。一个关键的区别是光谱观察到的n -> pi* 过渡的HPPD/Fe-II/PPA复合物，根据相关的密度泛函理论计算，建议从附近的残基和羧酸基团的α-酮酸之间的H-键合。这种相互作用将通过稳定羧酸根基团上的电子密度而不利于脱羧反应，使得不利于氧化裂解产生CO2。(c)2006年由Elsevier Inc.出版
The alpha-ketoglutate (alpha-KG)-dependent dioxygenases are a large class of mononuclear non-heme iron enzymes that require Fe-II, alpha-KG and dioxygen for catalysis, with the alpha-KG cosubstrate supplying the two additional electrons required for dioxygen activation. A subclass of these enzymes exists in which the a-keto acid is covalently attached to the substrate, including (4-hydroxy)mandelate synthase (HmaS) and (4-hydroxyphenyl)pyruvate dioxygenase (HPPD) which utilize the same substrate but exhibit two different general reactivities (H-atom abstraction and electrophilic attack). Previous kinetic studies of Streptomyces avermitilis HPPD have shown that the substrate analog phenylpyruvate (PPA), which only differs from the normal substrate (4-hydroxyphenyl)pyruvate (HPP) by the absence of a para-hydroxyl group on the aromatic ring, does not induce a reaction with dioxygen. While an Fe-IV=O intermediate is proposed to be the reactive species in converting substrate to product, the key step utilizing O-2 to generate this species is the decarboxylation of the alpha-keto acid. It has been generally proposed that the two requirements for decarboxylation are bidentate coordination of the a-keto acid to Felt and the presence of a 5C Fe-II site for the O-2 reaction. Circular dichroism and magnetic circular dichroism studies have been performed and indicate that both enzyme complexes with PPA are similar with bidentate a-KG coordination and a 5C Fe-II site. However, kinetic studies indicate that while HmaS reacts with PPA in a coupled reaction similar to the reaction with HPP, HPPD reacts with PPA in an uncoupled reaction at an similar to 10(5)-fold decreased rate compared to the reaction with HPP. A key difference is spectroscopically observed in the n -> pi* transition of the HPPD/Fe-II/PPA complex which, based upon correlation to density functional theory calculations, is suggested to result from H-bonding between a nearby residue and the carboxylate group of the alpha-keto acid. Such an interaction would disfavor the decarboxylation reaction by stabilizing electron density on the carboxylate group such that the oxidative cleavage to yield CO2 is disfavored. (c) 2006 Published by Elsevier Inc.