Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan.
J Chem Phys. 2009 Nov 28;131(20):205102. doi: 10.1063/1.3265985.
Yeast frataxin is a protein exhibiting cold denaturation at an exceptionally high temperature (280 K). We show that the microscopic mechanism of cold denaturation, which has recently been suggested by us [Yoshidome and Kinoshita, Phys. Rev. E 79, 030905(R) (2009)], is also applicable to yeast frataxin. The hybrid of the angle-dependent integral equation theory combined with the multipolar water model and the morphometric approach is employed for calculating hydration thermodynamic quantities of the protein with a prescribed structure. In order to investigate the characteristics of the cold-denatured structures of yeast frataxin, we consider the entropy change upon denaturation comprising the loss of the water entropy and the gain in the protein conformational entropy. The minimum and maximum values of the conformational-entropy gain (i.e., the range within which the exact value lies) are estimated via two routes. The range of the water-entropy loss is then determined from the entropy change experimentally obtained [Pastore et al., J. Am. Chem. Soc. 129, 5374 (2007)]. We calculate the water-entropy loss upon the transition from the native structure to a variety of unfolded structures. We then select the unfolded structures for which the water-entropy loss falls within the determined range. The selection is performed at cold and heat denaturation temperatures of yeast frataxin. The structures characterizing cold and heat denaturations are thus obtained. It is found that the average values of the radius of gyration, excluded volume, and water-accessible surface area for the cold-denatured structures are almost the same as those for the heat-denatured ones. We theoretically estimate the cold denaturation temperature of yeast frataxin from the experimental data for the enthalpy, entropy, and heat-capacity changes upon denaturation. The finding is that the temperature is considerably higher than 273 K. These results are in qualitatively good accord with the experimental observations.
酵母 frataxin 是一种在异常高温(280 K)下表现出冷变性的蛋白质。我们表明,最近我们提出的冷变性的微观机制[Yoshidome 和 Kinoshita, Phys. Rev. E 79, 030905(R) (2009)]也适用于酵母 frataxin。采用角度相关积分方程理论与多极水分子模型和形态学方法的混合方法,用于计算具有规定结构的蛋白质的水合热力学量。为了研究酵母 frataxin 冷变性结构的特性,我们考虑了变性过程中熵的变化,包括水熵的损失和蛋白质构象熵的增加。构象熵增加的最小值和最大值(即,确切值所在的范围)通过两种途径进行估计。然后从[Pastore 等人,J. Am. Chem. Soc. 129, 5374 (2007)]实验获得的熵变化来确定水熵损失的范围。我们计算了从天然结构转变为各种展开结构时的水熵损失。然后选择水熵损失落在确定范围内的展开结构。在酵母 frataxin 的冷和热变性温度下进行选择。因此获得了冷和热变性的结构特征。结果发现,冷变性结构的回转半径平均值、排除体积和可及水表面积与热变性结构几乎相同。我们根据变性过程中焓、熵和热容变化的实验数据,从理论上估计了酵母 frataxin 的冷变性温度。结果发现,温度远高于 273 K。这些结果与实验观察结果定性上非常吻合。