Baden N, Hirota S, Takabe T, Funasaki N, Terazima M
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
J Chem Phys. 2007 Nov 7;127(17):175103. doi: 10.1063/1.2780860.
Two intermediates observed for the folding process of apoplastocyanin (apoPC) were investigated by using a photoinduced triggering system combined with the transient grating and transient lens methods. The thermodynamic quantities, enthalpy, heat capacity, partial volume, and thermal expansion volume changes during the protein folding reaction were measured in time domain for the first time. An interesting observation is the positive enthalpy changes during the folding process. This positive enthalpy change must be compensated by positive entropy changes, which could be originated from the dehydration effect of hydrophobic residues and/or the translational entropy gain of bulk water molecules. Observed negative heat capacity change was explained by the dehydration effect of hydrophilic residues and/or motional confinement of amino acid side chains and water molecules in apoPC. The signs of the volume change and thermal expansion volume were different for two processes and these changes were interpreted in terms of the different relative contributions of the hydration and the dehydration of the hydrophilic residues. These results indicated two-step hydrophobic collapses in the early stage of the apoPC folding, but the nature of the dynamics was different.
利用光诱导触发系统结合瞬态光栅和瞬态透镜方法，对质体蓝素（apoPC）折叠过程中观察到的两种中间体进行了研究。首次在时域中测量了蛋白质折叠反应过程中的热力学量，即焓、热容、偏摩尔体积和热膨胀体积变化。一个有趣的发现是折叠过程中焓的正变化。这种正焓变必须由正熵变来补偿，这可能源于疏水残基的脱水效应和/或大量水分子的平移熵增加。观察到的负热容变化可以用亲水性残基的脱水效应和/或apoPC中氨基酸侧链和水分子的运动限制来解释。两个过程的体积变化和热膨胀体积的符号不同，这些变化可以根据亲水性残基水合和脱水的不同相对贡献来解释。这些结果表明，在apoPC折叠的早期阶段存在两步疏水塌缩，但动力学性质不同。
