Catanzano F, Graziano G, Fusi P, Tortora P, Barone G
Dipartimento di Chimica, Università di Napoli "Federico II", Italy.
Biochemistry. 1998 Jul 21;37(29):10493-8. doi: 10.1021/bi972994k.
Sso7d from the thermoacidophilic archaebacterium Sulfolobus solfataricus is a small globular protein with a known three-dimensional structure. Inspection of the structure reveals that Phe31 is a member of the aromatic cluster forming the protein hydrophobic core, whereas Trp23 is located on the protein surface and its side chain exposed to the solvent. The thermodynamic consequences of the substitution of these two residues in Sso7d have been investigated by comparing the temperature-induced denaturation of Sso7d with that of three mutants: F31A-Sso7d, F31Y-Sso7d, and W23A-Sso7d. The denaturation processes proved to be reversible for all proteins, and represented well by the two-state N if D transition model in a wide range of pH. All three mutants are less thermally stable than the parent protein; in particular, in the pH range of 5.0-7.0, the F31A substitution leads to a decrease of 24 degreesC in the denaturation temperature, the F31Y substitution to a decrease of 10 degreesC, and the W23A substitution to a decrease of 6 degreesC. A careful thermodynamic analysis of such experimental data is carried out.
来自嗜热嗜酸古细菌硫磺矿硫化叶菌的Sso7d是一种具有已知三维结构的小球状蛋白质。对该结构的检查表明，苯丙氨酸31是形成蛋白质疏水核心的芳香族簇的成员，而色氨酸23位于蛋白质表面，其侧链暴露于溶剂中。通过比较Sso7d与三个突变体（F31A-Sso7d、F31Y-Sso7d和W23A-Sso7d）的温度诱导变性，研究了Sso7d中这两个残基取代的热力学后果。结果表明，所有蛋白质的变性过程都是可逆的，并且在很宽的pH范围内都能很好地用两态N→D转变模型来表示。所有三个突变体的热稳定性都低于亲本蛋白质；特别是，在pH值为5.0-7.0的范围内，F31A取代导致变性温度降低24℃，F31Y取代导致降低10℃，W23A取代导致降低6℃。对这些实验数据进行了仔细的热力学分析。
