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

为了分析蛋白质构象原理，即蛋白质的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，有两个主要的小组：(1)对模型蛋白质--人溶菌酶的彻底研究和(2)关于蛋白质稳定性、蛋白质动力学和蛋白质折叠的重要项目的研究。对于第一个项目(Yutani、Yamagata和Kitao)，构建了100多个系统全面替代的突变型人溶菌酶。分别用量热法和X射线分析检测了突变引起的稳定性和结构的变化。在获得的稳定性结构数据库的基础上，考察了稳定性变化与结构突变之间的关系，并在充分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因变性而产生的可及表面积差异等因素后，成功地估计了稳定因子的各个参数。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影响不大；(2)如果由于取代作用去除了长度为3A的氢键，突变蛋白质的失稳幅度应为8.6kJ/mol；(3)当蛋白质内部新引入一个水分子时，由于熵效应，失稳幅度为7.2kJ/mol。对于第二个项目，Kidokoro和Yutani研究了嗜热菌蛋白质的稳定性。库希德自己开发了时间分辨烧孔光谱，并研究了锌取代肌红蛋白的构象波动和动力学。Kidera、Kataoka、Kujima和Goto研究了动力学、蛋白质折叠和蛋白质的非自然结构等重要问题。熊海和木谷郎还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.