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首页> 外文期刊>Journal of Molecular Biology >Thermodynamics of the coil == beta-sheet transition in a membrane environment.
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Thermodynamics of the coil == beta-sheet transition in a membrane environment.

机译：线圈在膜环境中的β-片层转变的热力学。

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摘要

Biologically important peptides such as the Alzheimer peptide Abeta(1-40) display a reversible random coil <==>beta-structure transition at anionic membrane surfaces. In contrast to the well-studied random coil left arrow over right arrow alpha-helix transition of amphipathic peptides, there is a dearth on information on the thermodynamic and kinetic parameters of the random coil left arrow over right arrow beta-structure transition. Here, we present a new method to quantitatively analyze the thermodynamic parameters of the membrane-induced beta-structure formation. We have used the model peptide (KIGAKI)(3) and eight analogues in which two adjacent amino acids were substituted by their d-enantiomers. The positions of the d,d pairs were shifted systematically along the three identical segments of the peptide chain. The beta-structure content of the peptides was measured in solution and when bound to anionic lipid membranes with circular dichroism spectroscopy. The thermodynamic binding parameters were determined with isothermal titration calorimetry and the binding isotherms were analysed by combining a surface partition equilibrium with the Gouy-Chapman theory. The thermodynamic parameters were found to be linearly correlated with the extent of beta-structure formation. beta-Structure formation at the membrane surface is characterized by an enthalpy change of DeltaH(beta)=-0.23 kcal/mol per residue, an entropy change of DeltaS(beta)=-0.24 cal/mol K residue and a free energy change of DeltaG(beta)=-0.15 kcal/mol residue. An increase in temperature induces an unfolding of beta-structure. The residual free energy of membrane-induced beta-structure formation is close to that of membrane-induced alpha-helix formation.
机译：具有生物学重要性的肽，例如阿尔茨海默氏肽Abeta（1-40）在阴离子膜表面显示出可逆的无规卷曲β结构转变。与经过精心研究的两亲性肽的右箭头α-螺旋过渡上的左旋箭头相反，缺少关于右箭头β-结构过渡上的随机螺旋左箭头的热力学和动力学参数的信息。在这里，我们提出了一种定量分析膜诱导的β-结构形成的热力学参数的新方法。我们使用了模型肽（KIGAKI）（3）和八个类似物，其中两个相邻的氨基酸被其d对映异构体取代。 d，d对的位置沿着肽链的三个相同部分系统地移动。肽的β结构含量在溶液中以及通过圆二色光谱法与阴离子脂质膜结合后进行测量。用等温滴定热法测定热力学结合参数，并结合表面分配平衡与Gouy-Chapman理论分析结合等温线。发现热力学参数与β结构形成的程度线性相关。在膜表面形成β结构的特征是每个残基的焓变化为DeltaHβ= -0.23 kcal / mol，熵的变化为DeltaSβ= -0.24 cal / mol K残基ΔGβ＝ -0.15kcal / mol残余物。温度升高引起β结构的展开。膜诱导的β-结构形成的残余自由能接近膜诱导的α-螺旋形成的残余自由能。

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