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首页> 外文期刊>Journal of Molecular Biology >pH-dependent interactions and the stability and folding kinetics of the N-terminal domain of L9. Electrostatic interactions are only weakly formed in the transition state for folding.
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pH-dependent interactions and the stability and folding kinetics of the N-terminal domain of L9. Electrostatic interactions are only weakly formed in the transition state for folding.

机译：pH依赖的相互作用以及L9 N末端结构域的稳定性和折叠动力学。静电相互作用仅在折叠的过渡状态下形成。

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摘要

The role of electrostatic interactions in the stability and the folding of the N-terminal domain of the ribosomal protein L9 (NTL9) was investigated by determining the effects of varying the pH conditions. Urea denaturations and thermal unfolding experiments were used to measure the free energy of folding, DeltaG degrees, at 18 different pH values, ranging from pH 1.1 to pH 10.5. Folding rates were measured at 19 pH values between pH 2.1 and pH 9.5, and unfolding rates were determined at 15 pH values in this range using stopped-flow fluorescence experiments. The protein is maximally stable between pH 5.5 and 7.5 with a value of DeltaG degrees =4.45 kcal mol(-1). The folding rate reaches a maximum at pH 5.5, however the change in folding rates with pH is relatively modest. Over the pH range of 2.1 to 5.5 there is a small increase in folding rates, ln (k(f)) changes from 5.1 to 6.8. However, the change in stability is more dramatic, with a difference of 2.6 kcal mol(-1) between pH 2.0 and pH 5.4. The change in stability is largely due to the smaller barrier for unfolding at low pH values. The natural log of the unfolding rates varies by approximately four units between pH 2.1 and pH 5.5. The stability of the protein decreases above pH 7.5 and again the change is largely due to changes in the unfolding rate. ln (k(f)) varies by less than one unit between pH 5.5 and pH 9.5 while DeltaG degrees decreases by 2.4 kcal mol(-1) over the range of pH 5. 4 to pH 10.0, which corresponds to a change in ln K(eq) of 4.0. These studies show that pH-dependent interactions contribute significantly to the overall stability of the protein but have only a small effect upon the folding kinetics, indicating that electrostatic interactions are weakly formed in the transition state for folding. Copyright 2000 Academic Press.
机译：通过确定不同pH条件的影响，研究了静电相互作用在核糖体蛋白L9（NTL9）N端结构域稳定性和折叠中的作用。尿素变性和热解折叠实验用于测量18种不同pH值（pH 1.1至pH 10.5）下的折叠自由能DeltaG度。在pH 2.1和pH 9.5之间的19个pH值下测量折叠速率，并使用停止流荧光实验在此范围内的15个pH值下确定解折叠速率。该蛋白在pH 5.5和7.5之间最大稳定，其DeltaG度= 4.45 kcal mol（-1）。折叠速率在pH 5.5时达到最大值，但是折叠速率随pH的变化相对较小。在2.1到5.5的pH范围内，折叠速率略有增加，ln（k（f））从5.1变为6.8。但是，稳定性的变化更为显着，pH 2.0和pH 5.4之间的差异为2.6 kcal mol（-1）。稳定性的变化很大程度上是由于在低pH值下展开的障碍较小。展开速率的自然对数在pH 2.1和pH 5.5之间变化大约四个单位。蛋白质的稳定性在pH 7.5以上降低，并且再次变化主要是由于解折叠速率的变化。 ln（k（f））在pH 5.5和pH 9.5之间变化小于一个单位，而DeltaG度在pH 5的范围内下降2.4 kcal mol（-1）。4至pH 10.0，这对应于ln的变化K（eq）为4.0。这些研究表明，pH依赖性相互作用对蛋白质的整体稳定性有显着贡献，但对折叠动力学的影响很小，这表明在折叠的过渡态中弱形成了静电相互作用。版权所有2000学术出版社。

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