タンパク質立体構造の安定性・ダイナミックス・折れたたみ機構

为了分析“蛋白质结构原理”，即蛋白质三维结构如何在其氨基酸序列中编码的原理，我们研究了蛋白质构象的物理化学方面。要做到这一点，有两个主要小组：(1)对模型蛋白质，人类溶菌酶的深入研究；(2)对蛋白质稳定性，蛋白质动力学和蛋白质折叠的重要项目进行研究。第一个项目（Yutani, Yamagata, Kitao）构建了100多个具有系统和全面替代的突变型人溶菌酶。通过量热法和x射线分析分别检测了突变引起的稳定性和结构变化。在得到的稳定性-结构数据库的基础上，考察了突变引起的稳定性变化与结构变化之间的关系，并考虑了二级结构倾向、水的引入、氢键的形成和去除、极性原子和非极性原子变性导致的可及表面积的差异等因素，成功估计了稳定因素的各个参数。这些结果表明：(1)非极性原子对蛋白质的稳定性起重要作用，而极性原子对蛋白质的稳定性不起作用；(2)如果一个长度为3 a的氢键因取代而被移除，突变蛋白的失稳量为8.6 kJ/mol;(3)当一个水分子新引入蛋白质内部时，由于熵效应，突变蛋白的失稳量为7.2 kJ/mol。在第二个项目中，Kidokoro和Yutani研究了嗜热菌蛋白质的稳定性。Kushide自己开发了时间分辨的空穴燃烧光谱，并检测了锌取代肌红蛋白的构象波动和动力学。Kidera, Kataoka， Kuwajima和Goto研究了动力学，蛋白质折叠和蛋白质非天然结构的重要问题。Kumagai和Kidokoro也研究了蛋白质功能的重要问题。

In order to analyze "principles of protein architecture", that is, the principle of how protein three-dimensional structures are coded for in their amino acid sequence, we have studied physico-chemical aspects of protein conformation. To do it there are two major groups : (1) a thorough study of a model protein, human lysozyme and (2) a study of important projects on protein stability, protein dynamics, and protein folding. As to the first project (Yutani, Yamagata, and Kitao), more than 100 mutant human lysozymes with systematic and comprehensive substitutions are constructed. Changes in stabilities and structures due to mutations were examined by calorimetry and X-ray analysis, respectively. On the basis of the obtained stability-structure data-base, the relationship between changes in stability and structure due to mutations was examined and each parameter of stabilization factors could be successfully estimated after due consideration on such as secondary structure propensity, introduction of water, formation and removal of hydrogen bond, differences in accessible surface area of polar and non-polar atoms due to denaturation. These results indicate that (1) non-polar atoms play an important role in protein stability but polar atoms do not, (2) if a hydrogen bond in which the length is 3 A is removed due to substitution, the mutant protein should be destabilized by 8.6 kJ/mol, (3) when one water molecule is newly introduced in the interior of a protein, it is destabilized by 7.2 kJ/mol due to entropic effect. As to the second project, Kidokoro and Yutani studied stability of proteins from thermophile. Kushide developed time-resolved hole-burning spectroscopy by himself and examined conformational fluctuations and dynamics of Zn-substituted myoglobin. Kidera, Kataoka, Kuwajima, and Goto studied important problems of dynamics, protein folding, and non-native structures of a protein. Kumagai and Kidokoro also studied important problems of protein function.