Anatomy of energetic changes accompanying urea-induced protein denaturation
Anatomy of energetic changes accompanying urea-induced protein denaturation
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DOI：
10.1073/pnas.0706251104
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发表时间：
2007-09-25
影响因子：
11.1
通讯作者：
Bolen, D. Wayne
中科院分区：
文献类型：
--
作者：
Auton, Matthew;Holthauzen, Luis Marcelo F.;Bolen, D. Wayne
由于其蛋白质变性能力，尿素在蛋白质折叠和展开的实验和概念理解中发挥了关键作用。尿素迫使蛋白质展开的能力由 m 值给出，m 值是一个实验量，给出每摩尔尿素展开的自由能变化。借助 Tanford 的转移模型 [Tanford C (11964) J Am Chem Soc 86:2050-2059]，我们使用新获得的从水到 1 M 尿素的蛋白质侧链和主链单元的基团转移自由能 (GTFE) 来解释尿素的 m 值，该方法根据新暴露的基团的残留水平自由能贡献揭示了蛋白质变性的解剖结构。变性。 GTFE 是通过考虑甘氨酸从水中转移到 1 M 尿素时的溶解度和活度系数比来获得的。与一些研究人员的观点相反，GTFE 表明尿素不会通过与非极性侧链的有利相互作用使蛋白质变性；尿素诱导的蛋白质解折叠的驱动因素是尿素与肽骨架的良好相互作用。尽管据说 m 值与变性时新暴露的表面积成正比，但只有约 25% 的面积有利于去折叠（因为新暴露的主链单元），约 75% 的面积适度地反对尿素诱导的变性（源自侧链暴露）。使用转移模型和新确定的 GTFE 实现了长期追求的目标，即在单个氨基酸残基水平上预测尿素依赖性协同蛋白解折叠能量。
Because of its protein-denaturing ability, urea has played a pivotal role in the experimental and conceptual understanding of protein folding and unfolding. The measure of urea's ability to force a protein to unfold is given by the m value, an experimental quantity giving the free energy change for unfolding per molar urea. With the aid of Tanford's transfer model [Tanford C (11964) J Am Chem Soc 86:2050-2059], we use newly obtained group transfer free energies (GTFEs) of protein side-chain and backbone units from water to 1 M urea to account for the m value of urea, and the method reveals the anatomy of protein denaturation in terms of residue-level free energy contributions of groups newly exposed on denaturation. The GTFEs were obtained by accounting for solubility and activity coefficient ratios accompanying the transfer of glycine from water to 1 M urea. Contrary to the opinions of some researchers, the GTFEs show that urea does not denature proteins through favorable interactions with nonpolar side chains; what drives urea-induced protein unfolding is the large favorable interaction of urea with the peptide backbone. Although the m value is said to be proportional to surface area newly exposed on denaturation, only approximate to 25% of the area favorably contributes to unfolding (because of newly exposed backbone units), with approximate to 75% modestly opposing urea-induced denaturation (originating from side-chain exposure). Use of the transfer model and newly determined GTFEs achieves the long-sought goal of predicting urea-dependent cooperative protein unfolding energetics at the level of individual amino acid residues.