Hamada D, Kuroda Y, Tanaka T, Goto Y
Department of Biology Faculty of Science, Osaka University, Japan.
J Mol Biol. 1995 Dec 8;254(4):737-46. doi: 10.1006/jmbi.1995.0651.
It is generally assumed that peptide fragments derived from globular proteins are either unfolded, or adopt native-like secondary structures, in particular alpha-helix, which are similar to those occurring in the early stages of protein folding. Since the structured conformations of short peptides are unstable, 2,2,2-trifluoroethanol (TFE) is often used to stabilize them. To examine the folding process of beta-proteins, we synthesized three fragments of beta-lactoglobulin corresponding to two beta-strands and one helix region, and examined their conformation by circular dichroism and nuclear magnetic resonance. These regions were chosen because, according to secondary structure prediction, all three should have high helix propensities. In aqueous solution, the three peptides had only a little ordered structure, but when TFE was added, they exhibited marked helical propensities, as also observed for the whole molecule of beta-lactoglobulin. These results indicate that the intrinsic helical propensity of a peptide fragment elucidated by the addition of TFE is not necessarily related to the secondary structure in the native state. The results further suggest a case of non-hierarchical protein folding model, in which non-native structures may be involved in the early stage of folding.
一般认为，源自球状蛋白质的肽片段要么是未折叠的，要么呈现出类似天然的二级结构，特别是α-螺旋，这与蛋白质折叠早期阶段出现的结构相似。由于短肽的结构化构象不稳定，2,2,2-三氟乙醇（TFE）常被用于稳定它们。为了研究β-蛋白质的折叠过程，我们合成了β-乳球蛋白的三个片段，分别对应两条β-链和一个螺旋区域，并通过圆二色性和核磁共振研究了它们的构象。选择这些区域是因为根据二级结构预测，这三个区域都应该具有较高的螺旋倾向。在水溶液中，这三个肽只有很少的有序结构，但加入TFE后，它们表现出明显的螺旋倾向，β-乳球蛋白的整个分子也是如此。这些结果表明，通过加入TFE阐明的肽片段的内在螺旋倾向不一定与天然状态下的二级结构相关。结果进一步表明了一种非分层蛋白质折叠模型的情况，其中非天然结构可能参与折叠的早期阶段。
