Oxygen activation by the noncoupled binuclear copper site in peptidylglycine α-hydroxylating monooxygenase. Reaction mechanism and role of the noncoupled nature of the active site
Oxygen activation by the noncoupled binuclear copper site in peptidylglycine α-hydroxylating monooxygenase. Reaction mechanism and role of the noncoupled nature of the active site
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DOI：
10.1021/ja031564g
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发表时间：
2004-04-21
影响因子：
15
通讯作者：
Solomon, EI
中科院分区：
文献类型：
--
作者：
Chen, P;Solomon, EI
采用密度泛函方法计算了具有非偶联双核Cu活性中心的肽基甘氨酸α-羟基化单加氧酶（PHM）的反应热力学和势能面.两种可能的单核Cu/O-2物种已被评估，2-电子还原的Cu-M（II）-OOH中间体和1-电子还原侧上的Cu-M（II）-superoxo中间体，这可能会形成具有可比的热力学在催化Cum网站。通过Cu-M（II）-OOH中间体的底物H-原子提取反应被发现是化学上可接近的，由于甲硫氨酸配体的贡献，但具有高活化势垒（类似于37 kcal/mol，在3.0埃的活性位点/底物距离），反对Cu-M（II）-OOH物种作为PHM中的反应性Cu/O-2中间体。相反，侧位Cu-M（II）-superoxo中间体从底物上夺取H原子是一个几乎等能的过程，在活性位/底物距离相当的情况下（类似于14 kcal/mol）具有低反应势垒，表明侧位Cu-M（II）-superoxo是PHM中的活性物种。Cu-M（II）-OOH和Cu-M（II）-superoxo物种的差异反应性与它们参与H原子提取反应的不同前线分子轨道相关。在H-原子提取之后，用于底物羟基化的合理途径涉及“水辅助”的直接OH转移到底物自由基，其产生高能量的Cu-M（II）-氧基物种。这为分子内电子从Cu-H位点转移以完成PHM中的反应提供了必要的驱动力。的铜-M（II）-OOH和铜-M（II）-superoxo中间体之间的差分反应模式提供洞察PHM和多巴胺β-单加氧酶活性位点的非耦合性质的作用，相比，耦合双核铜活性位点的血蓝蛋白，酪氨酸酶，儿茶酚氧化酶，在O-2激活。
Reaction thermodynamics and potential energy surfaces are calculated using density functional methods to investigate possible reactive Cu/O-2 species for H-atom abstraction in peptidylglycine a-hydroxylating monooxygenase (PHM), which has a noncoupled binuclear Cu active site. Two possible mononuclear Cu/O-2 species have been evaluated, the 2-electron reduced Cu-M(II)-OOH intermediate and the 1-electron reduced side-on Cu-M(II)-superoxo intermediate, which could form with comparable thermodynamics at the catalytic Cum site. The substrate H-atom abstraction reaction by the Cu-M(II)-OOH intermediate is found to be thermodynamically accessible due to the contribution of the methionine ligand, but with a high activation barrier (similar to37 kcal/mol, at a 3.0-Angstrom active site/substrate distance), arguing against the Cu-M(II)-OOH species as the reactive Cu/O-2 intermediate in PHM. In contrast, H-atom abstraction from substrate by the side-on Cu-M(II)-superoxo intermediate is a nearly isoenergetic process with a low reaction barrier at a comparable active site/substrate distance (similar to14 kcal/mol), suggesting that side-on Cu-M(II)-superoxo is the reactive species in PHM. The differential reactivities of the Cu-M(II)-OOH and Cu-M(II)-superoxo species correlate to their different frontier molecular orbitals involved in the H-atom abstraction reaction. After the H-atom abstraction, a reasonable pathway for substrate hydroxylation involves a "water-assisted" direct OH transfer to the substrate radical, which generates a high-energy Cu-M(II)-oxyl species. This provides the necessary driving force for intramolecular electron transfer from the Cu-H site to complete the reaction in PHM. The differential reactivity pattern between the Cu-M(II)-OOH and Cu-M(II)-superoxo intermediates provides insight into the role of the noncoupled nature of PHM and dopamine beta-monooxygenase active sites, as compared to the coupled binuclear Cu active sites in hemocyanin, tyrosinase, and catechol oxidase, in O-2 activation.