Evans P A, Kautz R A, Fox R O, Dobson C M
Inorganic Chemistry Laboratory, University of Oxford, U.K.
Biochemistry. 1989 Jan 10;28(1):362-70. doi: 10.1021/bi00427a050.
The equilibrium between alternative folded states of a globular protein, staphylococcal nuclease, has been investigated by using 1H NMR. Magnetization-transfer experiments have revealed the existence of a related structural heterogeneity of the unfolded state, and quantitative analysis of a series of these experiments has permitted the kinetics of folding and interconversion of the different states to be explored. A model based on cis/trans isomerism at the peptide bond preceding Pro-117 has been developed to account for the results. This model, recently supported by a protein-engineering experiment [Evans et al. (1987) Nature (London) 329, 266], has been used to interpret the kinetic data, providing insight into the nature of the folding processes. The predominance of the cis-proline form in the folded state is shown to derive from a large favorable enthalpy term resulting from more effective overall folding interactions. The kinetics of folding and isomerization are shown to occur on similar time scales, such that more than one pathway between two states may be significant. It has been possible, however, to compare the direct folding and unfolding rates within the cis- and trans-proline-containing populations, with results suggesting that the specific stabilization of the cis peptide bond is effective only at a late stage in the folding process.
利用核磁共振氢谱（1H NMR）研究了球状蛋白葡萄球菌核酸酶不同折叠态之间的平衡。磁化转移实验揭示了未折叠态存在相关的结构异质性，对一系列此类实验的定量分析使得对不同状态的折叠和相互转化动力学进行探索成为可能。基于脯氨酸-117之前肽键的顺/反异构现象建立了一个模型来解释这些结果。这个模型最近得到了一个蛋白质工程实验[埃文斯等人（1987年），《自然》（伦敦）329卷，266页]的支持，已被用于解释动力学数据，从而深入了解折叠过程的本质。结果表明，折叠态中顺式脯氨酸形式占主导地位源于更有效的整体折叠相互作用产生的大量有利焓项。折叠和异构化动力学显示发生在相似的时间尺度上，因此两个状态之间可能不止一条途径是重要的。然而，已经能够比较含顺式和反式脯氨酸群体内的直接折叠和解折叠速率，结果表明顺式肽键的特定稳定作用仅在折叠过程的后期有效。
