Studies on protein structure-function relationship by de novo design

从头设计了Cro蛋白(Isogai等人，J.Mol.Biol)。354,801-814,2005)及其核心变异体的合成来研究蛋白质折叠的序列依赖性。设计的Cro蛋白随着温度的升高以一种非合作的、异常的方式展开，而天然的Lambda噬菌体Cro蛋白表现出合作展开，其中二级结构在相同的时间过程中崩溃。在设计的蛋白质中，α螺旋逐渐破坏的速度比β片状的慢。折叠不合作的程度，或折叠中间体的稳定性，与形成不溶性蛋白质聚集体或淀粉样纤维的倾向有关。这些结果表明，可以从折叠成明确结构的序列中进一步选择显示协同折叠的氨基酸序列，并且这种天然的折叠特性代表了自然发生的序列选择的驱动力之一。天然蛋白质可能在选择性压力下获得了折叠协同性，以避免在分子进化过程中形成有毒聚集体或淀粉样纤维。

The de novo designed Cro protein (Isogai, et al., J.Mol.Biol. 354, 801-814, 2005) and its core variants were synthesized to investigate the sequence dependence of the protein folding. The designed Cro proteins unfold in a non-cooperative, anomalous manner with temperature increased, whereas the native lambda phage Cro protein exhibits cooperative unfolding, in which the secondary structures collapse in the identical time courses. In the designed proteins, α helices gradually disrupted slower than β sheets. The degree of the folding non-cooperativety, or stability of folding intermediate, correlates with the tendency to form insoluble protein aggregate or amyloid fibrils. The present results indicate that amino acid sequences exhibiting cooperative folding can be further selected from the sequences that fold into a well-defined structure, and that the native-like folding properties represent one of the driving forces in naturally occurring sequence selection. Native proteins may have acquired their folding cooperativity under selective pressure to avoid formation of the toxic aggregate or amyloid fibrils in the molecular evolution.