Finkelstein A V, Badretdinov A Y, Ptitsyn O B
Institute of Protein Research, Academy of Sciences of the USSR, Moscow Region.
Proteins. 1991;10(4):287-99. doi: 10.1002/prot.340100403.
It was recently found that some short peptides (including C- and S-peptide fragments of RNase A) can have considerable helicity in solution, which was considered to be surprising. Does the observed helicity require a new explanation, or is it consistent with previous understanding? In this work we show that this helicity is consistent with the physical theory of secondary structure based on an extension of the conventional Zimm-Bragg model. Without any special modifications, this theory explains reasonably well almost all the experimentally observed dependencies of helicity on pH, temperature, and amino acid replacements. We conclude that the observed "general level" of helicity of C- and S-peptides (5-30% at room temperature and 10-50% near 0 degrees C) is "normal" for short peptides consisting mainly of helix-forming and helix-indifferent residues. The helicity is modified by a multitude of weak specific side chain interactions, many of which are taken into account by the present theory; some discrepancies between the theory and experiment can be explained by weak side-chain-side chain interactions that were neglected. A reasonable coincidence of the theory with experiment suggests that it had been used to investigate the role of local interactions in the formation of alpha-helical "embryos" in unfolded protein chains.
最近发现一些短肽（包括核糖核酸酶A的C肽和S肽片段）在溶液中可具有相当可观的螺旋度，这被认为是令人惊讶的。观察到的螺旋度是需要新的解释，还是与先前的认识一致呢？在这项工作中，我们表明这种螺旋度与基于传统齐姆-布拉格模型扩展的二级结构物理理论是一致的。无需任何特殊修改，该理论就能很好地解释几乎所有实验观察到的螺旋度对pH、温度和氨基酸替换的依赖性。我们得出结论，对于主要由形成螺旋和对螺旋无偏好的残基组成的短肽而言，观察到的C肽和S肽螺旋度的“一般水平”（室温下为5%-30%，接近0摄氏度时为10%-50%）是“正常的”。螺旋度会受到多种弱的特定侧链相互作用的影响，本理论考虑了其中许多相互作用；理论与实验之间的一些差异可以用被忽略的弱侧链-侧链相互作用来解释。理论与实验的合理吻合表明，它已被用于研究局部相互作用在未折叠蛋白链中α螺旋“胚胎”形成中的作用。
