Nagi A D, Regan L
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
Fold Des. 1997;2(1):67-75. doi: 10.1016/S1359-0278(97)00007-2.
The loops in proteins are less well characterized than the secondary structural elements that they connect. We have used the four-helix-bundle protein Rop as a model system in which to explore the role of loop length in protein folding and stability.
A natural two-residue loop was replaced with a series of glycine linkers up to 10 residues in length. All 10 mutants are highly helical dimers that retain wild-type RNA-binding activity. As loop length is increased, the stability of Rop toward thermal and chemical denaturation is progressively decreased.
All the mutants assume a wild-type-like structure, which suggests that the natural loop does not actively dictate the final protein fold. The strong inverse correlation observed between loop length and stability is well described by a simple polymer model in which the entropy of loop closure is the dominant energetic term. Our results emphasize the importance of optimization of loop length to successful protein design.
蛋白质中的环结构比它们所连接的二级结构元件的特征描述得更少。我们使用四螺旋束蛋白Rop作为模型系统，以探索环长度在蛋白质折叠和稳定性中的作用。
一个天然的两残基环被一系列长度达10个残基的甘氨酸连接子所取代。所有10个突变体都是高度螺旋化的二聚体，保留了野生型RNA结合活性。随着环长度的增加，Rop对热变性和化学变性的稳定性逐渐降低。
所有突变体都呈现出类似野生型的结构，这表明天然环并不主动决定最终的蛋白质折叠。环长度与稳定性之间观察到的强负相关可以通过一个简单的聚合物模型很好地描述，其中环闭合的熵是主要的能量项。我们的结果强调了优化环长度对成功进行蛋白质设计的重要性。
