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蛋白质变性状态的展开度决定了脲:从稳定化吉布斯自由能角度看尿素与甲胺的拮抗作用。

Unfoldness of the denatured state of proteins determines urea: Methylamine counteraction in terms of Gibbs free energy of stabilization.

机构信息

School of Biotechnology, Yeungnam University, Gyeongsan 712-749, South Korea.

Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi 110025, India.

出版信息

Int J Biol Macromol. 2019 Jul 1;132:666-676. doi: 10.1016/j.ijbiomac.2019.03.236. Epub 2019 Apr 1.

Abstract

In many tissues and organisms, large amount of urea gets accumulated to maintain osmotic balance. To evade the threatening impact of urea, living organisms accumulate methylamines, a class of osmolytes, in proportion of 2:1 (urea:methylamine). To understand underlying cause(s) for protein-specific counteraction behavior, thermodynamic stability (ΔG) of three disulfide free proteins (myoglobin, bovine cytochrome c and barstar) in the mixture of urea and methylamine has been estimated from guanidinium chloride-(GdmCl) driven denaturation curves. Using the experimentally measured values of ΔG obtained in the presence of individual methylamines and urea, we predicted the molar ratio of urea and a methylamine required for perfect compensation for each of the proteins. Interestingly, for all proteins studied, a similar ratio has been observed for perfect compensation. The predicted ratio for perfect compensation in terms of thermodynamic parameters was about 2:1 M ratio of urea to methylamine. Furthermore, a partial counteraction was observed in the myoglobin and barstar. However, for bovine cytochrome c, perfect compensation was observed in both GdmCl- and heat-driven denaturations. Our observations clearly suggest that the counteraction phenomenon depends on the extent of the unfolding of the denatured states of proteins.

摘要

在许多组织和生物中,大量的尿素会积累以维持渗透平衡。为了避免尿素的威胁,生物会以 2:1(尿素:甲基胺)的比例积累甲基胺,这是一类渗透调节剂。为了了解蛋白质特异性拮抗行为的潜在原因,我们从胍盐酸盐(GdmCl)驱动的变性曲线估计了三种无二硫键蛋白(肌红蛋白、牛细胞色素 c 和 barnase)在尿素和甲基胺混合物中的热力学稳定性(ΔG)。利用在单个甲基胺和尿素存在下测量的 ΔG 的实验值,我们预测了每种蛋白质完全补偿所需的尿素和甲基胺的摩尔比。有趣的是,对于所有研究的蛋白质,都观察到了完全补偿的相似比例。在热力学参数方面,完全补偿的预测比值约为 2:1,即尿素与甲基胺的摩尔比。此外,在肌红蛋白和 barnase 中观察到部分拮抗作用。然而,对于牛细胞色素 c,在 GdmCl 和热驱动变性中都观察到了完全补偿。我们的观察结果清楚地表明,拮抗现象取决于蛋白质变性状态的展开程度。

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