NMR structures of two designed proteins with high sequence identity but different fold and function
NMR structures of two designed proteins with high sequence identity but different fold and function
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DOI：
10.1073/pnas.0805857105
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发表时间：
2008-09-23
影响因子：
11.1
通讯作者：
Orban, John
中科院分区：
文献类型：
--
作者：
He, Yanan;Chen, Yihong;Orban, John
蛋白质序列如何编码 3D 结构仍然是生物学中的一个基本问题。理解折叠密码的一种方法是设计一对具有最大序列同一性但保留不同折叠的蛋白质。因此，非同一性必须负责确定哪种折叠拓扑占主导地位并构成折叠特定的折叠代码。我们最近设计了两种蛋白质，G(A)88 和 G(B)88，具有 88% 的序列同一性，但折叠和功能不同 [Alexander et al. (2007)Proc Natl Acad Sci USA 104:1196311968]。在这里，我们描述了通过 NMR 光谱在溶液中测定的这些蛋白质的详细 3D 结构。尽管存在大量突变，序列同一性水平为 16% 至 88%，但 G(A)88 和 G(B)88 分别保持其独特的野生型 3-α 和 α/β 折叠。据我们所知，对具有如此高序列同一性但不同折叠拓扑的两种单体蛋白进行 3D 结构测定是前所未有的。七个不同残基（总共 56 个）的几何形状提供了对 3-α 和 α/β 构象之间转换的结构基础的深入了解。这些非同一性的子集在 G(A)88 和 G(B)88 结构的指导下进一步突变，会产生具有更高水平的序列同一性 (95%) 和不同折叠的蛋白质。因此，仅通过小蛋白质中的少量突变就可以实现向具有相当稳定性的替代单体折叠的构象转换。这一结果不仅有助于理解折叠代码，而且有助于理解新折叠的演变。
How protein sequence codes for 3D structure remains a fundamental question in biology. One approach to understanding the folding code is to design a pair of proteins with maximal sequence identity but retaining different folds. Therefore, the nonidentities must be responsible for determining which fold topology prevails and constitute a fold-specific folding code. We recently designed two proteins, G(A)88 and G(B)88, with 88% sequence identity but different folds and functions [Alexander et al. (2007) Proc Natl Acad Sci USA 104:1196311968]. Here, we describe the detailed 3D structures of these proteins determined in solution by NMR spectroscopy. Despite a large number of mutations taking the sequence identity level from 16 to 88%, G(A)88 and G(B)88 maintain their distinct wild-type 3-alpha and alpha/beta folds, respectively. To our knowledge, the 3D-structure determination of two monomeric proteins with such high sequence identity but different fold topology is unprecedented. The geometries of the seven nonidentical residues (of 56 total) provide insights into the structural basis for switching between 3-alpha and alpha/beta conformations. Further mutation of a subset of these nonidentities, guided by the G(A)88 and G(B)88 structures, leads to proteins with even higher levels of sequence identity (95%) and different folds. Thus, conformational switching to an alternative monomeric fold of comparable stability can be effected with just a handful of mutations in a small protein. This result has implications for understanding not only the folding code but also the evolution of new folds.