Hydrogen exchange in chymotrypsin inhibitor 2 probed by denaturants and temperature
Hydrogen exchange in chymotrypsin inhibitor 2 probed by denaturants and temperature
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DOI：
10.1006/jmbi.1997.1049
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发表时间：
1997-07-04
影响因子：
5.6
通讯作者：
Fersht, AR
中科院分区：
文献类型：
--
作者：
Itzhaki, LS;Neira, JL;Fersht, AR
胰凝乳蛋白酶抑制剂2的氢交换已被测量在低浓度的GdmCl的存在下，在不同的温度。在不同温度下交换的研究使我们能够获得局部交换过程的活化能谱，以及封闭的、交换不胜任的形式和开放的、交换胜任的形式之间的焓变化。从GdmCl交换的依赖性，m值，这是一个新的表面积暴露于溶剂在开放和封闭的形式之间的平衡的措施，可以确定为个别质子。因此，该参数提供了关于开环反应的结构性质的信息。在没有变性剂的情况下，来自原生态和类原生态的交换占主导地位。随着GdmCl浓度的增加，涉及全局展开的开放反应选择性地促进大多数酰胺质子。出现三类质子：对于一组质子，有一个线性和弱依赖变性剂，表明占主导地位的开放反应是相同的整个范围内的GdmCl浓度，并涉及局部波动与曝光的小新的表面。对于另一组质子，交换最慢的残基，观察到线性的，但更强的变性剂依赖性。对于这些质子，全球展开占主导地位，和m-值是类似的平衡GdmCl变性在相同条件下通过荧光测量得到的。对于其余的质子，GdmCl的依赖性是弱的，在低GdmCl浓度和增加在较高的GdmCl浓度。无法确定次全球发展的任何部分。相反，所有的质子似乎合并在一起，在高GdmCl浓度的全球展开反应。(C)出版社：Academic Press Limited。
Hydrogen exchange of chymotrypsin inhibitor 2 has been measured in the presence of low concentrations of GdmCl and at different temperatures. The study of exchange at different temperatures allows us to obtain the activation enthalpies for the local exchange processes, and the change in enthalpy between the closed, exchange-incompetent, forms and the open, exchange-competent, forms. From the GdmCl dependence of exchange, an m-value, which is a measure of the new surface area exposed to solvent in the equilibrium between open and closed forms, can be determined for individual protons. This parameter therefore provides information about the structural nature of the opening reactions. Ln the absence of denaturant, exchange from native and native-like states dominates. As GdmCl concentration is increased, opening reactions that involve global unfolding are selectively promoted for the majority of amide protons. Three classes of protons emerge: for one set of protons, there is a linear and weak dependence on denaturant, indicating that the dominant opening reaction is the same throughout the range of GdmCl concentrations and involves local fluctuations with exposure of little new surface. For another set of protons, the most slowly exchanging residues, a linear, but much stronger, denaturant dependence is observed. For these protons, global unfolding dominates, and the m-values are similar to that obtained by equilibrium GdmCl denaturation measured by fluorescence under identical conditions. For the remaining protons, the GdmCl-dependence is weak at low GdmCl concentrations and increases at higher GdmCl concentrations. No segment of sub-global unfolding could be identified. Rather, all protons appear to merge together at high GdmCl concentrations to the global unfolding reaction. (C) 1997 Academic Press Limited.