Tamura A, Sturtevant J M
Department of Chemistry, Yale University, New Haven, CT 06520, USA.
J Mol Biol. 1995 Jun 9;249(3):646-53. doi: 10.1006/jmbi.1995.0325.
Amino acid replacements of Met73, which is hyper-exposed in the native structure, with Asp, Glu, Lys, Gly, Ala, Val, Leu or Ile changed the stability of Streptomyces subtilism inhibitor by +1.60 to -0.94 kcal/mol-1 in free energy at 82.21 degrees C at pH 7.0, with higher hydrophobicity of the replacing amino acid side-chain showing a correlation with lower stability. Thermodynamic parameters obtained from detailed calorimetric analyses gave a nearly proportional relation between the entropy change and the enthalpy change of denaturation, i.e. T delta delta S degrees = -0.03 (+/- 0.11) + 1.14 (+/- 0.03) delta delta H, with the linear correlation coefficient 0.996 for 18 data points. This proportionality observed uniquely for the substitutions at position 73 was caused primarily by the water/side-chain interaction, or hydration effect, which can account for the majority of the changes in enthalpy and entropy induced by the mutations.
在pH 7.0、82.21摄氏度条件下，将天然结构中高度暴露的甲硫氨酸73分别替换为天冬氨酸、谷氨酸、赖氨酸、甘氨酸、丙氨酸、缬氨酸、亮氨酸或异亮氨酸后，枯草芽孢杆菌链霉菌抑制剂的稳定性在自由能方面改变了+1.60至-0.94千卡/摩尔-1，取代氨基酸侧链疏水性越高，稳定性越低。通过详细的量热分析获得的热力学参数表明，变性的熵变和焓变之间存在近似比例关系，即TΔΔS° = -0.03（±0.11）+ 1.14（±0.03）ΔΔH，18个数据点的线性相关系数为0.996。在73位取代中唯一观察到的这种比例关系主要是由水/侧链相互作用或水合作用引起的，这可以解释突变引起的大部分焓变和熵变。
