Kautz R A, Fox R O
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511.
Protein Sci. 1993 May;2(5):851-8. doi: 10.1002/pro.5560020514.
Thermally unfolded staphylococcal nuclease has been rapidly quenched to temperatures near 0 degree C and the refolding behavior examined using an NMR kinetic experiment. Unfolded protein, exhibiting random coil chemical shifts, persists following the quench and refolds in two distinct kinetic phases. A protein folding intermediate with a trans Lys 116-Pro 117 peptide bond is transiently overpopulated and relaxes to the predominantly cis native cis-trans equilibrium. The rate of trans-->cis isomerization in the native-like nuclease intermediate is approximately 100-fold faster than that observed in a Lys-Pro model peptide. The activation enthalpy of 20 kcal/mol observed for the nuclease Lys 116-Pro 117 peptide bond is comparable to that observed for other X-Pro isomerizations.
热变性的葡萄球菌核酸酶已被迅速淬灭至接近0摄氏度的温度，并使用核磁共振动力学实验研究其重折叠行为。淬灭后，呈现无规卷曲化学位移的未折叠蛋白持续存在，并以两个不同的动力学阶段进行重折叠。具有反式赖氨酸116-脯氨酸117肽键的蛋白质折叠中间体短暂地过度富集，并松弛到主要为顺式的天然顺反平衡状态。在类天然核酸酶中间体中，反式→顺式异构化的速率比在赖氨酸-脯氨酸模型肽中观察到的速率快约100倍。核酸酶赖氨酸116-脯氨酸117肽键观察到的20千卡/摩尔的活化焓与其他X-脯氨酸异构化观察到的活化焓相当。
