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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Exploring Flory's isolated-pair hypothesis: Statistical mechanics of helix-coil transitions in polyalanine and the C-peptide from RNase A
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Exploring Flory's isolated-pair hypothesis: Statistical mechanics of helix-coil transitions in polyalanine and the C-peptide from RNase A

机译：探索弗洛里的孤立对假设：聚丙氨酸和来自RNase A的C肽的螺旋螺旋转变的统计力学

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摘要

To evaluate Flory's isolated-pair hypothesis in the context of helical peptides, we explore equilibrium conformations of α-helix-forming polypeptides as a function of temperature by means of replica exchange molecular dynamics in conjunction with the CHARMM/GB implicit solvent force field and the weighted histogram analysis method) From these simulations, Zimm-Bragg parameters, s and σ, of Ac-Ala_n-NMe are computed as a function of temperature. The values obtained for s(T) and σ(T) remain unchanged along the length of the polypeptide except for very short chains and yield results consistent with measurements based on short helix-forming peptides but suggest larger s values than anticipated from polymer-based measurements. From direct estimates of the density of states for Ac-Ala_n-NMe (n = 3-20) and peptide constructs based on the C peptide from RNase A, the conformational entropy is calculated versus temperature. The calculated S(T) shows a clear proportionality to the chain length over a wide range of temperature. This is observed in polypeptides with both significantly branched and simple methyl (alanine) side chains. These results provide evidence for the validity of Flory's isolated pair hypothesis, at least in the context of helical peptides and helix-to-coil transitions in these peptides.
机译：为了在螺旋肽的背景下评估Flory的孤立对假设，我们通过副本交换分子动力学，结合CHARMM / GB隐性溶剂作用力场和分子动力学，探索了α-螺旋形成多肽的平衡构象随温度的变化。加权直方图分析方法）从这些模拟中，计算Ac-Ala_n-NMe的Zimm-Bragg参数s和σ作为温度的函数。除了非常短的链外，沿着多肽的长度获得的s（T）和σ（T）值保持不变，并且产量结果与基于短螺旋形成肽的测量结果一致，但建议的s值比基于聚合物的预期更大测量。从直接估计Ac-Ala_n-NMe（n = 3-20）和基于RNase A的C肽的肽构建体的状态密度，可以计算构象熵随温度的变化。计算得出的S（T）在很宽的温度范围内与链长呈明显比例关系。这在具有明显支链和简单甲基（丙氨酸）侧链的多肽中观察到。这些结果至少在螺旋肽和这些肽中的螺旋到螺旋过渡的背景下提供了弗洛里分离对假设的有效性的证据。

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