Spectroscopic and geometric variations in perturbed blue copper centers: Electronic structures of stellacyanin and cucumber basic protein
Spectroscopic and geometric variations in perturbed blue copper centers: Electronic structures of stellacyanin and cucumber basic protein
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DOI：
10.1021/ja980606b
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发表时间：
1998-09-23
影响因子：
15
通讯作者：
Solomon, EI
中科院分区：
文献类型：
--
作者：
LaCroix, LB;Randall, DW;Solomon, EI
通过结合低温光吸收、圆二色性和磁性圆二色性光谱与密度泛函计算的结果，定义了扰动蓝铜蛋白stellacyanin（STC）和黄瓜碱性蛋白CBP（也称为plantacyanin，PNC）相对于质体蓝蛋白PLC中“经典”位点的电子结构.此外，提出了产碱菌野生型和M121 Q天青蛋白的吸收和磁性圆二色光谱，并分别与PLC和STC进行比较。这些研究表明，CBP/PNC中的主要电子结构变化，相对于PLC，是配体场跃迁向更高能量的小位移和Cu d（x2-y2）半填充HOMO的旋转，这增加了伪σ并降低了半胱氨酸（Cys）硫与Cu d（x2-y2）的π相互作用，此外，将一些甲硫氨酸（Met）硫特征混合到HOMO中。负责扰动的电子结构的几何畸变，相对于PLC，涉及一个耦合的角运动的Cys和Met残基朝向一个更扁平的tetrahydropylene结构。与CBP/PNC相反，STC（其具有被Gln取代的轴向Met）使其配体场跃迁转移到较低能量，并且经历小得多的HOMO旋转和Cys伪σ/π混合程度;在HOMO中没有显示轴向谷氨酰胺特征。这些变化表明STC中的四面体畸变。因此，扰动的光谱特征与相对于PLC的四面体和四面体几何畸变一致。这些扰动是根据这些蛋白质中增加的轴向配体强度来讨论的（即，CBP/PNC中的短Cu-S（Met）和STC中的短Cu-S（Gln））。这诱导了类似于α（u）样的扭曲力，其导致位点的四重扭曲（CBP/PNC）或在结构上受到蛋白质（STC和M121 Q）的限制。
The electronic structures of the perturbed blue copper proteins stellacyanin (STC) and cucumber basic protein (CBP, also called plantacyanin, PNC) are defined relative to that of the well-understood "classic" site found in plastocyanin (PLC) by combining the results of low-temperature optical absorption, circular dichroism, and magnetic circular dichroism spectra with density functional calculations. Additionally, absorption and magnetic circular dichroism spectra of Alcaligenes denitrificans wild-type and M121Q azurin are presented and compared to PLC and STC, respectively. These studies show that the principal electronic structure changes in CBP/PNC, with respect to PLC, are a small shift of the ligand field transitions to higher energy and a rotation of the Cu d(x2-y2) half-filled HOMO which increases the pseudo-sigma and decreases the pi interactions of the cysteine (Cys) sulfur with Cu d(x2-y2) and, in addition, mixes some methionine (Met) sulfur character into the HOMO. The geometrical distortion responsible for the perturbed electronic structure, relative to PLC, involves a coupled angular movement of the Cys and Met residues toward a more flattened tetragonal structure. In contrast to CBP/PNC, STC (which has the axial Met substituted by Gin) has its ligand field transitions shifted to lower energy and undergoes much smaller degrees of HOMO rotation and Cys pseudo-sigma/pi mixing; no axial glutamine character is displayed in the HOMO. These changes indicate a tetrahedral distortion in STC. Therefore, perturbed spectral features are consistent with both tetragonal and tetrahedral geometric distortions relative to PLC. These perturbations are discussed in terms of the increased axial ligand strength in these proteins (i.e., short Cu-S(Met) in CBP/PNC and O epsilon(Gln) in STC). This induces an similar to epsilon(u)-like distorting force which either results in a tetragonal distortion of the site (CBP/PNC) or is structurally restrained by the protein (STC and M121Q).