牛血清IgG热化学变性和热变性的研究

使用差示扫描量热仪(DSC)和荧光光谱法研究了在pH 7.4时牛血清IgG (bIgG)热变性, 热化学变性和等温化学变性过程(变性剂为尿素和盐酸胍), 首次报道了bIgG在热化学变性和等温化学变性过程中的相关热力学参数. DSC和荧光光谱实验结果表明, bIgG的热变性和热化学变性过程都是较复杂的不可逆过程, 这个过程可被看作一个三态变构过程. DSC实验表明在热化学变性过程中bIgG的变性温度和焓变值会随着环境中的变性剂浓度的升高而降低. 使用荧光光谱法对bIgG在尿素或盐酸胍存在下的等温化学变性过程进行了研究, 结果显示bIgG的化学变性过程也是一个较复杂的非二态过程. 实验数据分析表明, 变性剂尿素和盐酸胍与bIgG之间主要是依靠氢键相互作用的, 而热变性过程中bIgG的凝集是由于bIgG热变性时结构改变后暴露出的疏水结构互相作用造成的. 实验结果还表明单纯的热变性只能导致bIgG的不完全变性, 而即使是在高浓度变性剂存在时的bIgG热化学变性, 尿素和盐酸胍分别导致的bIgG热化学变性的去折叠态也是不同的.

Study on Thermal and Thermal Chemical Denaturation of Bovine Immunoglobulin G

The thermal denaturation, isothermal chemical denaturation and thermal chemical denaturation of bovine immunoglobulin G (bIgG) at pH 7.4 were studied by differential scanning calorimetry (DSC) and fluorescence spectroscopy adopting guanidine hydrochloride (GuHCl) and urea as denaturant. The thermodynamic parameters of thermal and chemical denaturation were determined for bIgG using both methods. The experimental results of DSC and fluorescence spectroscopy showed that the thermal denaturation and thermal chemical denaturation of bIgG were both a complex irreversible process, and might follow a three-state mechanism. Isothermal chemical denaturation studies of bIgG were carried out in the presence of GuHCl or urea to observe that denaturant induced isothermal chemical denaturation of bIgG also followed a multistate process. The thermal denaturation measured in the presence of the denaturant displayed that the transition temperature and enthalpy change on denaturation of bIgG strongly depended on denaturant concentration, and GuHCl and urea interacted with bIgG primarily by hydrogen bonds, yielding a randomly coiled conformation in its unfolded state, while thermal denaturation produced an incompletely unfolded aggregation of bIgG. Therefore, both chemical denaturation methods can yield different structurally unfolded states of the bIgG.