Polar residues in the protein core of Escherichia coli thioredoxin are important for fold specificity
Polar residues in the protein core of Escherichia coli thioredoxin are important for fold specificity
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DOI：
10.1021/bi010427y
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发表时间：
2001-08-28
期刊：
影响因子：
2.9
通讯作者：
Mayo, SL
中科院分区：
文献类型：
--
作者：
Bolon, DN;Mayo, SL
大多数球状蛋白质含有疏水残基的核心，其在折叠状态下不可接近溶剂。一般来说，核中的极性残基在热力学上是不利的，除非它们能够形成分子内氢键。与疏水相互作用相比，极性相互作用在性质上更具方向性，并且可以有助于折叠特异性。在对263个球状蛋白质结构的调查中，我们发现核心位置的极性残基数量与蛋白质大小之间存在很强的正相关性。为了探索埋藏的极性残基的重要性，我们实验测试了大肠杆菌硫氧还蛋白中五个极性核心残基的疏水突变的影响。具有单个疏水突变的蛋白质（D26I、C32A、C35A、T66L和T77V）都具有与野生型（wt）类似的协同解折叠转变，如通过化学变性所确定的。相对于野生型，D26 I更稳定，而其他点突变体不太稳定。组合的5倍突变体蛋白（IAALV）比野生型稳定性差，并且具有比野生型显著更不协同的解折叠转变。NMR光谱以及酰胺氘交换表明，IAALV可能是一些低能量的结构在折叠状态下采样，这表明在核心的极性残基是重要的指定一个良好的折叠天然结构。
Most globular proteins contain a core of hydrophobic residues that are inaccessible to solvent in the folded state. In general, polar residues in the core are thermodynamically unfavorable except when they are able to form intramolecular hydrogen bonds. Compared to hydrophobic interactions, polar interactions are more directional in character and may aid in fold specificity. In a survey of 263 globular protein structures, we found a strong positive correlation between the number of polar residues at core positions and protein size. To probe the importance of buried polar residues, we experimentally tested the effects of hydrophobic mutations at the five polar core residues in Escherichia coli thioredoxin. Proteins with single hydrophobic mutations (D26I, C32A, C35A, T66L, and T77V) all have cooperative unfolding transitions like the wild type (wt), as determined by chemical denaturation. Relative to wt, D26I is more stable while the other point mutants are less stable. The combined 5-fold mutant protein (IAALV) is less stable than wt and has an unfolding transition that is substantially less cooperative than that of wt. NMR spectra as well as amide deuterium exchange indicate that IAALV is likely sampling a number of low-energy structures in the folded state, suggesting that polar residues in the core are important for specifying a well-folded native structure.