Variable-temperature, variable-field magnetic circular dichroism studies of tris-hydroxy- and mu3-oxo-bridged trinuclear Cu(II) complexes: evaluation of proposed structures of the native intermediate of the multicopper oxidases.
Variable-temperature, variable-field magnetic circular dichroism studies of tris-hydroxy- and mu3-oxo-bridged trinuclear Cu(II) complexes: evaluation of proposed structures of the native intermediate of the multicopper oxidases.
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DOI：
10.1021/ja0525152
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发表时间：
2005-09
影响因子：
15
通讯作者：
Jungjoo Yoon;Liviu M. Mirica;T. Stack;E. Solomon
中科院分区：
文献类型：
--
作者：
Jungjoo Yoon;Liviu M. Mirica;T. Stack;E. Solomon
多金属氧化物酶催化O2的4E-还原为H2O。完全还原的酶与O2反应生成天然中间体(NI)，它由四个氧化的铜中心组成，其中三个形成一个三核簇位，所有这些都由O2完全还原的产物连接起来。NI的最大特征是强磁性圆二色伪A特征(一对符号相反的与温度相关的C项)，它与O-->；Cu(II)配体-金属电荷转移(LMCT)有关，该电荷转移源于三核位置上的强Cu-O键。在本研究中，通过对相关模型化合物TrisOH和Mu3O的光谱和电子结构的研究，对三核中心的两种最可能的铜-氧结构--三-MU2-羟基桥联结构和Mu3-氧-桥联结构进行了评价。研究发现，TrisOH的伪A项的两个分量与金属中心激发态自旋轨道耦合(SOC)耦合的同一个铜的LMCT相关，而对于Mu3O，它们与LMCT相关，不同的铜中心通过氧中心激发态SOC耦合。基于这两个候选模型的分析，只有Mu3-氧代桥联结构与NiI的光谱性质一致。MU3-氧桥联结构中的CuO-Sigma键将为O2的4E-还原提供热力学推动力，并允许电子方便地转移到三核团簇中的所有铜中心，这与其参与催化循环是一致的。
Multicopper oxidases catalyze the 4e- reduction of O2 to H2O. Reaction of the fully reduced enzyme with O2 produces the native intermediate (NI) that consists of four oxidized Cu centers, three of which form a trinuclear cluster site, all bridged by the product of full O2 reduction. The most characteristic feature of NI is the intense magnetic circular dichroism pseudo-A feature (a pair of temperature-dependent C-terms with opposite signs) associated with O --> Cu(II) ligand-to-metal charge transfer (LMCT) that derives from the strong Cu-O bonds in the trinuclear site. In this study, the two most plausible Cu-O structures of the trinuclear site, the tris-mu2-hydroxy-bridged and the mu3-oxo-bridged structures, are evaluated through spectroscopic and electronic structure studies on relevant model complexes, TrisOH and mu3O. It is found that the two components of a pseudo-A-term for TrisOH are associated with LMCT to the same Cu that are coupled by a metal-centered excited-state spin-orbit coupling (SOC), whereas for mu3O they are associated with LMCT to different Cu centers that are coupled by oxo-centered excited state SOC. Based on this analysis of the two candidate models, only the mu3-oxo-bridged structure is consistent with the spectroscopic properties of NI. The Cu-O sigma-bonds in the mu3-oxo-bridged structure would provide the thermodynamic driving force for the 4e- reduction of O2 and would allow the facile electron transfer to all Cu centers in the trinuclear cluster that is consistent with its involvement in the catalytic cycle.