Haezebrouck P, Joniau M, Van Dael H, Hooke S D, Woodruff N D, Dobson C M
Interdisciplinary Research Centre, Kortrijk, Belgium.
J Mol Biol. 1995 Feb 24;246(3):382-7. doi: 10.1006/jmbi.1994.0093.
Temperature-induced unfolding of human lysozyme has been monitored by circular dichroism and by nuclear magnetic resonance experiments at a variety of low pH values. The results indicate that, although at pH values above 3 unfolding appears to be consistent with a two-state model, at lower pH values this is not the case. At pH 1.2, for example, unfolding of the tertiary structure occurs at a temperature approximately 10 deg. C lower than that of the secondary structure. At 60 degrees C there is no detectable native tertiary structure remaining for human lysozyme at pH 1.2, although far-UV CD results show preservation of some 40% of the signal attributable to alpha-helical elements in the protein. This indicates the existence of a partially folded state of human lysozyme at low pH that has at least some characteristics of the well-defined molten globule state of the homologous alpha-lactalbumins and of the kinetic intermediates observed in the folding of alpha-lactalbumins and of c-type lysozymes. These results suggest that the absolute distinction between these two groups of proteins in terms of their different unfolding behaviour is not valid, and provide insights into possible features stabilizing such states.
通过圆二色性和核磁共振实验，在多种低pH值条件下监测了温度诱导的人溶菌酶的去折叠过程。结果表明，虽然在pH值高于3时，去折叠似乎符合两态模型，但在较低pH值时情况并非如此。例如，在pH 1.2时，三级结构的去折叠发生温度比二级结构的去折叠温度低约10℃。在60℃时，在pH 1.2条件下，人溶菌酶没有可检测到的天然三级结构残留，尽管远紫外圆二色性结果表明，蛋白质中约40%的信号可归因于α-螺旋元件得以保留。这表明在低pH值条件下，人溶菌酶存在一种部分折叠状态，该状态至少具有同源α-乳白蛋白明确的熔融球状体状态以及在α-乳白蛋白和c型溶菌酶折叠过程中观察到的动力学中间体的一些特征。这些结果表明，这两组蛋白质在不同去折叠行为方面的绝对区分是无效的，并为稳定此类状态的可能特征提供了见解。
