Cooper A
Chemistry Department, Glasgow University, Scotland, UK.
Biophys Chem. 2000 May 31;85(1):25-39. doi: 10.1016/s0301-4622(00)00136-8.
Large changes in heat capacity (deltaCp) have long been regarded as the characteristic thermodynamic signature of hydrophobic interactions. However, similar effects arise quite generally in order-disorder transitions in homogeneous systems, particularly those comprising hydrogen-bonded networks, and this may have significance for our understanding of protein folding and other biomolecular processes. The positive deltaCp associated with unfolding of globular proteins in water, thought to be due to hydrophobic interactions, is also typical of the values found for the melting of crystalline solids, where the effect is greatest for the melting of polar compounds, including pure water. This suggests an alternative model of protein folding based on the thermodynamics of phase transitions in hydrogen-bonded networks. Folded proteins may be viewed as islands of cooperatively-ordered hydrogen-bonded structure, floating in an aqueous network of less-well-ordered H-bonds in which the degree of hydrogen bonding decreases with increasing temperature. The enthalpy of melting of the protein consequently increases with temperature. A simple algebraic model, based on the overall number of protein and solvent hydrogen bonds in folded and unfolded states, shows how deltaCp from this source could match the hydrophobic contribution. This confirms the growing view that the thermodynamics of protein folding, and other interactions in aqueous systems, are best described in terms of a mixture of polar and non-polar effects in which no one contribution is necessarily dominant.
长期以来，热容的大幅变化（ΔCp）一直被视为疏水相互作用的特征性热力学标志。然而，在均相系统的有序 - 无序转变中，特别是那些包含氢键网络的系统中，也普遍会出现类似的效应，这可能对我们理解蛋白质折叠及其他生物分子过程具有重要意义。与球状蛋白质在水中展开相关的正ΔCp，被认为是由于疏水相互作用引起的，这也是晶体固体熔化时所发现的值的典型特征，其中对于包括纯水在内的极性化合物的熔化，这种效应最为显著。这表明基于氢键网络中相变热力学的蛋白质折叠替代模型。折叠的蛋白质可被视为协同有序的氢键结构岛，漂浮在氢键有序程度较低的水性网络中，其中氢键程度随温度升高而降低。因此，蛋白质的熔化焓随温度升高。一个基于折叠态和未折叠态蛋白质及溶剂氢键总数的简单代数模型，展示了来自此来源的ΔCp如何与疏水贡献相匹配。这证实了一种越来越流行的观点，即蛋白质折叠的热力学以及水性系统中的其他相互作用，最好用极性和非极性效应的混合来描述，其中没有一种贡献必然占主导地位。
