An XAS investigation of product and inhibitor complexes of Ni-containing GlxI from Escherichia coli: mechanistic implications.
An XAS investigation of product and inhibitor complexes of Ni-containing GlxI from Escherichia coli: mechanistic implications.
复制标题
对大肠杆菌含 Ni GlxI 的产物和抑制剂复合物的 XAS 研究：机理意义。
DOI：
10.1021/bi0018537
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发表时间：
2001
期刊：
影响因子：
2.9
通讯作者：
Maroney,MJ
中科院分区：
文献类型：
--
作者：
Davidson,G;Clugston,SL;Honek,JF;Maroney,MJ
大肠杆菌糖苷酶I（GlxI）是一种金属异构酶，其最大程度地被Ni 2+激活，不同于其他已知的对Zn 2+有活性的GlxI酶。该金属由两个水合配体，两个组氨酸（5和74）和两个谷氨酸（56和122）配位。对E.通过分析从酶和与产物S-d-乳酰谷胱甘肽和各种抑制剂形成的复合物获得的Ni K边X射线吸收光谱（XAS）数据来研究coliNi-GlxI。X射线吸收近边结构（XANES）的分析被用来确定各种Ni-GlxI配合物中的Ni位点的配位数和几何形状。从扩展X射线吸收精细结构（EXAFS）的分析得到的镍网站结构的度量细节。S-D-乳酰谷胱甘肽（产品）或辛基谷胱甘肽与酶的相互作用没有改变的Ni网站的结构。然而，XAS数据的分析从与结合到Ni-GlxI的肽异羟肟酸盐形成的复合物中获得，这与通过置换两个水分子而结合到Ni中心的抑制剂一致。该复合物的XANES分析与五配位金属最佳拟合，并且考虑到保留两个组氨酸配体的事实，表明谷氨酸配体的损失。谷氨酸配体的损失将保留在Ni络合物上的中性电荷，并且与在该络合物中Ni K-边缘能量中缺乏显著偏移一致。这些数据进行了比较，从E。coliNi-GlxI硒代蛋氨酸取代酶。天然酶中的三个甲硫氨酸残基与硒代蛋氨酸的替代不影响镍网站的结构。然而，添加肽异羟肟酸盐抑制剂导致形成复合物，其结构通过XAS分析确定，与通过置换两个水分子但保留组氨酸和谷氨酸配体的抑制剂结合一致。这导致阴离子络合物，这与观察到的Ni K边缘能量降低1.7 eV一致。合理的反应机制Ni-GlxI的结构信息进行了讨论。
Escherichia coliglyoxalase I (GlxI) is a metalloisomerase that is maximally activated by Ni2+, unlike other known GlxI enzymes which are active with Zn2+. The metal is coordinated by two aqua ligands, two histidines (5 and 74), and two glutamates (56 and 122). The mechanism ofE. coliNi-GlxI was investigated by analyzing Ni K-edge X-ray absorption spectroscopic (XAS) data obtained from the enzyme and complexes formed with the product,S-d-lactoylglutathione, and various inhibitors. The analysis of X-ray absorption near edge structure (XANES) was used to determine the coordination number and geometry of the Ni site in the various Ni-GlxI complexes. Metric details of the Ni site structure were obtained from the analysis of extended X-ray absorption fine structure (EXAFS). Interaction ofS-d-lactoylglutathione (product) or octylglutathione with the enzyme did not change the structure of the Ni site. However, analysis of XAS data obtained from a complex formed with a peptide hydroxamate bound to Ni-GlxI is consistent with this inhibitor binding to the Ni center by displacement of both water molecules. XANES analysis of this complex is best fit with a five-coordinate metal and, given the fact that both histidine ligands are retained, suggests the loss of a glutamate ligand. The loss of a glutamate ligand would preserve the neutral charge on the Ni complex and is consistent with the lack of a significant shift in the Ni K-edge energy in this complex. These data are compared with data obtained from theE. coliNi-GlxI selenomethionine-substituted enzyme. The replacement of three methionine residues in the native enzyme with selenomethionine does not affect the structure of the Ni site. However, addition of the peptide hydroxamate inhibitor leads to the formation of a complex whose structure as determined by XAS analysis is consistent with inhibitor binding via displacement of both water molecules but retention of both histidine and glutamate ligands. This leads to an anionic complex, which is consistent with an observed 1.7 eV decrease in the Ni K-edge energy. Plausible reaction mechanisms for Ni-GlxI are discussed in light of the structural information available.