Membrane partitioning: "classical" and "nonclassical" hydrophobic effects.
Membrane partitioning: "classical" and "nonclassical" hydrophobic effects.
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DOI：
10.1007/s00232-010-9321-y
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发表时间：
2011-01
影响因子：
2.4
通讯作者：
Ladokhin, Alexey S.
中科院分区：
文献类型：
--
作者：
Fernandez-Vidal, Monica;White, Stephen H.;Ladokhin, Alexey S.
非极性溶质从水到脂双层的转移自由能通常由较大的负焓控制，而不是由疏水效应所预期的较大的正熵控制。这种常见的观察结果导致了一种观点，即膜分配是由“非经典”疏水效应驱动的。我们用等温滴定量热法(ITC)和圆二色谱(CD)表征了研究得很好的蜂毒素多肽的分配，从而研究了这种现象。我们研究了蜂毒素在不同两性和阴离子混合脂类脂膜中分配自由能的熵(−TΔS)和焓(ΔH)分量(ΔG)的温度依赖性。我们发现，随着温度、脂质成分和囊泡大小的变化，熵和热焓分量显著变化，但ΔG(熵-热焓补偿值)变化很小。与分配相关的热容有一个很大的负值，约为−0.5千卡−−1和K−1。这一疏水效应的标志被发现与脂类组成无关。测量的热容用于计算疏水效应自由能ΔG hΦ，我们发现该自由能主导蜂毒素的分配，而与脂类组成无关。对于阴离子膜，额外的自由能来自库仑吸引，由于膜界面缺乏疏水和静电相互作用的可加性，库仑吸引具有较小的有效多肽电荷[Ladokhin and White J Mol Biol 309：543-552，]。我们的结果表明，不需要一种特殊的效应--非经典的疏水效应--来描述脂类双层的分配。
The free energy of transfer of nonpolar solutes from water to lipid bilayers is often dominated by a large negative enthalpy rather than the large positive entropy expected from the hydrophobic effect. This common observation has led to the idea that membrane partitioning is driven by the “nonclassical” hydrophobic effect. We examined this phenomenon by characterizing the partitioning of the well-studied peptide melittin using isothermal titration calorimetry (ITC) and circular dichroism (CD). We studied the temperature dependence of the entropic (−TΔS) and enthalpic (ΔH) components of free energy (ΔG) of partitioning of melittin into lipid membranes made of various mixtures of zwitterionic and anionic lipids. We found significant variations of the entropic and enthalpic components with temperature, lipid composition and vesicle size but only small changes in ΔG (entropy–enthalpy compensation). The heat capacity associated with partitioning had a large negative value of about −0.5 kcal mol−1 K−1. This hallmark of the hydrophobic effect was found to be independent of lipid composition. The measured heat capacity values were used to calculate the hydrophobic-effect free energy ΔG hΦ, which we found to dominate melittin partitioning regardless of lipid composition. In the case of anionic membranes, additional free energy comes from coulombic attraction, which is characterized by a small effective peptide charge due to the lack of additivity of hydrophobic and electrostatic interactions in membrane interfaces [Ladokhin and White J Mol Biol 309:543–552, ]. Our results suggest that there is no need for a special effect—the nonclassical hydrophobic effect—to describe partitioning into lipid bilayers.
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