Facchiano F, Ragone R, Porcelli M, Cacciapuoti G, Colonna G
Department of Biochemistry and Biophysics, University of Naples, Italy.
Eur J Biochem. 1992 Mar 1;204(2):473-82. doi: 10.1111/j.1432-1033.1992.tb16657.x.
The effect of temperature on the molecular structure of propylamine transferase from Sulfolobus solfataricus has been investigated. Sulfolobus solfataricus is an extreme thermophilic archaebacterium with an optimum living condition at 90 degrees C. The enzyme is an oligomeric (trimer) protein of molecular mass 112 kDa. The frictional ratio for the native protein suggests an irregularly shaped compact globular structure. The protein matrix is well organized as suggested by far ultraviolet circular dichroism at 25 degrees C (18% alpha helix, 43% beta structure, 19% beta bends and 20% unordered: root mean square = 7). Structural effects of temperature were investigated over 25-85 degrees C. The protein retains its quaternary structure in this temperature range. A highly reversible subtle conformational transition was detected by numerous structure-dependent techniques over 40-50 degrees C, with a midpoint centered at 45 degrees C. Functional data also support this view. In fact, two enzyme forms, characterized by different catalytic properties, are present in solution. The Arrhenius plot suggests the occurrence of two different activation-energy-dependent processes, one at a temperature higher and one at a temperature lower than 45 degrees C. The transition has been considered as a molecular switch between two protein populations at equilibrium with different functional and structural properties, temperature modulated. A physiological role for the molecular switch has also been postulated. The protein also shows some subtle and reversible spectroscopic changes around 75 degrees C. The molecular basis of the thermophilic nature of this enzyme seems to reside in its capability to dynamically couple catalytic and structural events to the thermal properties of the ambient medium.
研究了温度对嗜热栖热硫化叶菌丙胺转移酶分子结构的影响。嗜热栖热硫化叶菌是一种极端嗜热古细菌，最佳生存条件为90摄氏度。该酶是一种分子量为112 kDa的寡聚体（三聚体）蛋白质。天然蛋白质的摩擦比表明其具有不规则形状的紧密球状结构。如25摄氏度下的远紫外圆二色性所示（18%的α螺旋、43%的β结构、19%的β转角和20%的无序结构：均方根=7），蛋白质基质组织良好。在25-85摄氏度范围内研究了温度的结构效应。该蛋白质在这个温度范围内保持其四级结构。在40-50摄氏度范围内，通过多种结构依赖性技术检测到一个高度可逆的微妙构象转变，中点位于45摄氏度。功能数据也支持这一观点。事实上，溶液中存在两种具有不同催化特性的酶形式。阿累尼乌斯图表明存在两个不同的活化能依赖性过程，一个在高于45摄氏度的温度下，一个在低于45摄氏度的温度下。该转变被认为是处于平衡状态的两个具有不同功能和结构特性的蛋白质群体之间的分子开关，受温度调节。还推测了该分子开关的生理作用。该蛋白质在75摄氏度左右也显示出一些微妙且可逆的光谱变化。这种酶嗜热性质的分子基础似乎在于其能够将催化和结构事件与周围介质的热性质动态耦合。
