Colaneri Michael J, Vitali Jacqueline
Department of Chemistry and Physics, State University of New York at Old Westbury , Old Westbury, New York 11568, United States.
J Phys Chem A. 2014 Jul 3;118(26):4688-94. doi: 10.1021/jp500981c. Epub 2014 Jun 19.
Electron paramagnetic resonance (EPR) temperature-dependent measurements were undertaken on three Cu(II)-doped metal-histidine complexes to assess copper site dynamic behavior. Previous single-crystal EPR analysis on two of these, zinc d,l-histidine pentahydrate (ZnDLH) and bis(l-histidinato)cadmium dihydrate (CdLH), found that doped Cu(2+) can be modeled as hopping between two neighboring conformational states, with a temperature-dependent rate becoming large enough at room temperature to produce an "averaged" spectrum. By comparing spectra from their powdered form, we show that Cu(2+) doped into a third system, Cd(2+)-d,l-histidine (CdDLH), also exhibits temperature-dependent EPR with features indicating a similar motional-averaging process. In addition, the change of g and copper hyperfine parameters from low to high temperature for CdDLH resembles that in ZnDLH, whereas the change in these parameters for CdLH is like that found in a fourth copper-doped system, zinc l-histidine dihydrate (ZnLH). Taken together, these results suggest that averaging motion between neighboring copper sites is common in metal-bis(histidine) compounds. More detailed studies on biological models are thus warranted, especially because they reveal unique relationships between structure, dynamic processes, and stability and can lead to a better understanding of the role played by site flexibility in copper proteins.
对三种铜（II）掺杂的金属 - 组氨酸配合物进行了电子顺磁共振（EPR）温度相关测量，以评估铜位点的动态行为。之前对其中两种，即五水合锌d，l - 组氨酸（ZnDLH）和二水合双（l - 组氨酸）镉（CdLH）进行的单晶EPR分析发现，掺杂的Cu(2+)可以模拟为在两个相邻构象状态之间跳跃，其温度依赖速率在室温下变得足够大，从而产生“平均”光谱。通过比较它们粉末形式的光谱，我们表明，掺杂到第三种体系Cd(2+) - d，l - 组氨酸（CdDLH）中的Cu(2+)也表现出温度依赖的EPR，其特征表明存在类似的运动平均过程。此外，CdDLH从低温到高温的g和铜超精细参数变化类似于ZnDLH中的变化，而CdLH的这些参数变化则类似于在第四种铜掺杂体系二水合锌l - 组氨酸（ZnLH）中发现的变化。综合来看，这些结果表明相邻铜位点之间的平均运动在金属 - 双（组氨酸）化合物中很常见。因此，有必要对生物模型进行更详细的研究，特别是因为它们揭示了结构、动态过程和稳定性之间的独特关系，并有助于更好地理解位点灵活性在铜蛋白中所起的作用。
