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首页> 外文期刊>Journal of Molecular Biology >FREE ENERGY DETERMINANTS OF SECONDARY STRUCTURE FORMATION .2. ANTIPARALLEL BETA-SHEETS
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FREE ENERGY DETERMINANTS OF SECONDARY STRUCTURE FORMATION .2. ANTIPARALLEL BETA-SHEETS

机译：二级结构形成的自由能决定因素.2。反平行测试版

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The factors that determine the stability of antiparallel beta-she ets are considered via a theoretical analysis of conformational free energies. A series of idealized model polyalanine beta-sheets are built with constraints such that the angular geometry of hydrogen bonding varies in the range observed in proteins while hydrogen bonding distance remains fixed. The conformations of the sheets generated in this way have a broad distribution of twist angles ranging from highly twisted left-handed to highly twisted right-handed orientations. The association free energies of the sheets are calculated with a gas phase CHARMM potential and EDPB/gamma solvation models. Left-handed structures are found to be less stable than right handed structures due to intrachain steric hindrance in isolated left-handed strands. This explains why antiparallel beta-sheets in proteins are invariably twisted in the right-handed direction. The free energy surface for right-handed sheets shows particular preference for conformations ranging from flat to those that exhibit a pronounced right-handed twist. This suggests that antiparallel beta-sheets can adopt a variety of right-handed conformations, a result that is consistent with observations on known proteins. In parallel with our study of alpha-helices we find that van der Waals and hydrophobic interactions are the primary factor stabilizing polyalanine beta-sheets, while electrostatic interactions including hydrogen bonding are found to be destabilizing. However, in contrast to helices, the net change in conformational free energy involving only backbone-backbone interactions (including beta-carbons) is not sufficient to overcome the loss in configurational entropy that accompanies sheet formation. Rather we suggest that cross-strand non-polar side-chain-sidechain interactions are essential for sheet formation, explaining why large non-polar amino acids have the greatest sheet forming propensities. Thus, sheet propensities involve pairwise interactions and are expected to be context dependent, as has been observed in recent experiments. (C) 1995 Academic Press Limited [References: 30]
机译：通过构象自由能的理论分析来考虑确定反平行β-表的稳定性的因素。建立了一系列理想化的模型聚丙氨酸β-折叠，并具有一定的约束条件，使得氢键的角几何形状在蛋白质中观察到的范围内变化，而氢键的距离保持固定。以这种方式产生的片的构象具有宽的扭曲角分布，其范围从高度扭曲的左手取向到高度扭曲的右手取向。用气相CHARMM电势和EDPB /γ溶剂化模型计算板的缔合自由能。由于分离的左手链中的链内空间位阻，发现左手结构比右手结构不稳定。这就解释了为什么蛋白质中的反平行β-折叠总是沿右手方向扭曲。右旋片材的自由能表面显示出特别喜好的构象，范围从平坦到表现出明显的右旋扭曲的构象。这表明反平行β-折叠可以采用多种右旋构象，这一结果与对已知蛋白质的观察结果一致。在研究α-螺旋的同时，我们发现范德华力和疏水性相互作用是稳定聚丙氨酸β-折叠的主要因素，而包括氢键在内的静电相互作用却不稳定。然而，与螺旋相反，仅涉及主链-骨干相互作用（包括β-碳）的构象自由能的净变化不足以克服伴随薄片形成的构型熵的损失。相反，我们建议跨链非极性侧链-侧链相互作用对于薄片形成是必不可少的，这解释了为什么大的非极性氨基酸具有最大的薄片形成倾向。因此，如最近的实验中所观察到的那样，表层倾向涉及成对相互作用并且预期是上下文相关的。 （C）1995 Academic Press Limited [参考：30]

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