MECHANISM OF PROTEIN FOLDING--GLOBAL COUPLING

正如前几年所描述的那样，我们的研究得出了这样的假设 在某些单位的氨基酸序列折叠后，原子间 相互作用将在全球范围内耦合，以产生额外的能量，结果 在折叠和展开之间的平衡向有利于 折叠。这一假说并没有在机制方面得到检验。 和进化论的意义。因此，在完成热力学和 不变亮氨酸32和不变亮氨酸取代的动力学分析 马细胞色素c的部分不变亮氨酸35我们提出 亮氨酸32、色氨酸59和蛋氨酸80-S-血红素铁键是 相互作用才能产生这样的额外力量。替换的结果 不变的脯氨酸30和甘氨酸34也表明这些残基 将在维持这种耦合方面发挥作用。核磁共振谱研究 核糖核酸酶的氢交换(10-118)表明a)去除6个羧基 RNaseA的末端残基会破坏这些残基之间的偶联 而那些距离较远的物体，b)这又会改变焓-熵 补偿的方式使得吉布斯能量的大小发生变化 在没有大的折叠变化的情况下显著地减少了有利于折叠的情况， C)在这种激活状态下，分子将具有很高的运动性。 如前些年所报道的，卵裂的两个允许区域 与三个区域中的两个区域一致 在进化过程中插入了额外的氨基酸序列。因此，要 测试这种一致性意味着全局耦合的守恒性 一直在研究酵母细胞色素c的允许区。 到目前为止的结果表明，两个允许区域中的一个， 即在残基39到55之间(在马细胞色素c的编号中)可以 酵母是不允许的，可能是因为一个单一的 位由亮氨酸变为蛋氨酸等氨基酸。

As described in the previous years, our studies have led to the hypothesis that after folding of some unit of the amino acid sequences the interatomic interactions would be globally coupled to generate extra energy, resulting in shift of the equilibrium between folding and unfolding in favor of folding. This hypothesis is not being tested with respect to the mechanism and evoluntionary significance. Thus on completing thermodynamic and kinetic analyses of the effect of substitution of invariant leucine 32 and partially invariant leucine 35 of horse cytochrome c we have proposed that leucine 32, tryptophan 59 and the methionine 80-S-heme iron bond are coupled to generate such extra force. The results with substitution of invariant proline 30 and gylcine 34 have also suggested that these residues would have a role in maintaining such coupling. The NMR studies of hydrogen exchange of RNase (10-118) suggest that a) removal of 6 carboxy terminal residues of RNase A would disrupt coupling between these residues and those distant, b) this would, in turn, alter the enthalphy-entropy compensation in such a way that the magnitude of Gibbs energy change favoring folding is significantly reduced without a large change of fold, c) in this activated state the molecule would be highly motile. As reported in the previous years, the two permissible regions for cleavage of horse cytochrome c are consistent with two of the three regions where extra amino acid sequences have been inserted during evolution. Thus, to test where this consistency implies conservation of the global coupling we have been investigating the permissible regions with yeast cytochrome c. The results to date indicate that one of the two permissible regions, namely between residues 39 to 55 (in numbering of horse cytochrome c) may be non-permissible for yeast, possibly because of a change of a single amino acid such as change from leucine to methionine at position 64.