Britton K L, Baker P J, Borges K M, Engel P C, Pasquo A, Rice D W, Robb F T, Scandurra R, Stillman T J, Yip K S
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, England.
Eur J Biochem. 1995 May 1;229(3):688-95. doi: 10.1111/j.1432-1033.1995.tb20515.x.
In the light of the solution of the three-dimensional structure of the NAD(+)-linked glutamate dehydrogenase from the mesophile Clostridium symbiosum, we have undertaken a detailed examination of the alignment of the sequences for the thermophilic glutamate dehydrogenases from Thermococcus litoralis and Pyrococcus furiosus against the sequence and the molecular structure of the glutamate dehydrogenase from C. symbiosum, to provide insights into the molecular basis of their thermostability. This homology-based modelling is simplified by the relatively small number of amino acid substitutions between the two thermophilic glutamate dehydrogenase sequences. The most frequent amino acid exchanges involve substitutions which increase the hydrophobicity and sidechain branching in the more thermostable enzyme; particularly common is the substitution of valine to isoleucine. Examination of the sequence differences suggests that enhanced packing within the buried core of the protein plays an important role in maintaining stability at extreme temperatures. One hot spot for the accumulation of exchanges lies close to a region of the molecule involved in its conformational flexibility and these changes may modulate the dynamics of this enzyme and thereby contribute to increased stability.
鉴于嗜温共生梭菌中与NAD(+)相连的谷氨酸脱氢酶三维结构的解析，我们对来自嗜热栖热菌和激烈火球菌的嗜热谷氨酸脱氢酶序列与共生梭菌谷氨酸脱氢酶的序列及分子结构进行了详细比对，以深入了解其热稳定性的分子基础。由于两种嗜热谷氨酸脱氢酶序列之间的氨基酸替换数量相对较少，这种基于同源性的建模得以简化。最常见的氨基酸交换涉及那些能增加更耐热酶的疏水性和侧链分支的替换；缬氨酸替换为异亮氨酸尤为常见。对序列差异的研究表明，蛋白质埋藏核心区域内增强的堆积作用在维持极端温度下的稳定性方面起着重要作用。一个交换积累的热点区域靠近分子中与其构象灵活性相关的区域，这些变化可能会调节该酶的动力学，从而有助于提高稳定性。
