Davis-Searles P R, Morar A S, Saunders A J, Erie D A, Pielak G J
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.
Biochemistry. 1998 Dec 1;37(48):17048-53. doi: 10.1021/bi981364v.
Proteins denature at low pH because of intramolecular electrostatic repulsions. The addition of salt partially overcomes this repulsion for some proteins, yielding a collapsed conformation called the A-state. A-states have characteristics expected for the molten globule, a notional kinetic protein folding intermediate. Here we show that the addition of neutral sugars to solutions of acid-denatured equine ferricytochrome c induces formation of the A-state in the absence of added salt. We characterized the structure and stability of the sugar-induced A-state with circular dichroism spectropolarimetry (CD) and NMR-monitored hydrogen-deuterium exchange experiments. We also examined the stability of the sugar-induced A-state as a function of sugar size and concentration. The results are interpreted using several models and we conclude that the stabilizing effect is consistent with increased steric repulsion between the protein and the sugar solutions.
由于分子内静电排斥作用，蛋白质在低pH值下会变性。对于某些蛋白质而言，添加盐可部分克服这种排斥作用，产生一种称为A态的折叠构象。A态具有熔球态（一种概念性的蛋白质动力学折叠中间体）所预期的特征。在此我们表明，在不添加盐的情况下，向酸变性的马亚铁细胞色素c溶液中添加中性糖会诱导形成A态。我们用圆二色光谱偏振法（CD）和核磁共振监测的氢-氘交换实验对糖诱导的A态的结构和稳定性进行了表征。我们还研究了糖诱导的A态的稳定性与糖的大小和浓度之间的关系。使用几种模型对结果进行了解释，我们得出结论，稳定作用与蛋白质和糖溶液之间空间排斥作用的增加是一致的。
