Studies on protein structure-function relationship by de novo design

从头设计的Cro蛋白（Isogai等人，J.Mol.Biol.354，801-814，2005）及其核心变体以研究蛋白质折叠的序列依赖性。设计的Cro蛋白展开在一个非合作的，异常的方式与温度的增加，而天然λ噬菌体Cro蛋白表现出合作展开，其中二级结构崩溃在相同的时间过程。在设计的蛋白质中，α螺旋逐渐破坏的速度比β折叠慢。折叠非协同性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原纤维的趋势相关。本研究结果表明，表现出协同折叠的氨基酸序列可以进一步从折叠成明确定义的结构的序列中选择，并且天然样折叠特性代表了天然存在的序列选择中的驱动力之一。天然蛋白质在分子进化过程中可能在选择压力下获得了它们的折叠协同性，以避免形成有毒的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.