Cooper A, McAlpine A, Stockley P G
Department of Chemistry, Glasgow University, Scotland, UK.
FEBS Lett. 1994 Jul 4;348(1):41-5. doi: 10.1016/0014-5793(94)00579-6.
Calorimetric measurements of binding of a specific DNA fragment and S-adenosyl methionine (SAM) co-repressor molecules to the E. coli methionine repressor (MetJ) show significant differences in the energetics of binary and ternary protein-DNA complexes. Formation of the MetJ:SAM:DNA ternary complex is significantly more exothermic (delta H congruent to -99 kJ.mol-1) than either MetJ:DNA or MetJ:SAM binary complexes alone (delta H congruent to -10 kJ.mol-1 each). The protein is also significantly more stable to unfolding (delta Tm congruent to 5.4 degrees C) when bound to DNA. These observations suggest that binding of SAM to the protein-DNA complex leads to a significant reduction in dynamic flexibility of the ternary complex, with considerable entropy-enthalpy compensation, not necessarily involving any overall conformational change.
对特定DNA片段和S-腺苷甲硫氨酸（SAM）共阻遏物分子与大肠杆菌甲硫氨酸阻遏蛋白（MetJ）结合的量热测量表明，二元和三元蛋白质-DNA复合物的能量学存在显著差异。MetJ:SAM:DNA三元复合物的形成比单独的MetJ:DNA或MetJ:SAM二元复合物放热得多（ΔH约为-99 kJ·mol-1）（单独的MetJ:DNA和MetJ:SAM二元复合物的ΔH约为-10 kJ·mol-1）。当与DNA结合时，该蛋白质对解折叠也更稳定（ΔTm约为5.4℃）。这些观察结果表明，SAM与蛋白质-DNA复合物的结合导致三元复合物的动态灵活性显著降低，伴有相当大的熵-焓补偿，不一定涉及任何整体构象变化。
