Lane A N, Lefèvre J F, Jardetzky O
Biochim Biophys Acta. 1986 May 27;867(1-2):45-56. doi: 10.1016/0167-4781(86)90028-x.
We have determined the effect of the tryptophan (trp) repressor from Escherichia coli on the structure and dynamics of dA20dT20. The structure was determined using time-dependent nuclear Overhauser effects and spin-lattice relaxation times. The deoxyribose conformation is near C3' endo for the thymine residues, and a mixture of about 30% C3' endo and 70% C2' endo for the adenine residues. The glycosidic torsion angles are -50 degrees for T and -60 degrees for A. The roll is 20 degrees and the propellor twist is about 29 degrees. The conformation is consistent with recent calculations (Rao, K. and Kollman, P.A. (1985) J. Am. Chem. Soc. 107, 1507-1511). The rate constant for exchange of the imino protons is similar to that usually found for AT base-pairs, with an activation energy of 20 +/- 2 kcal/mol, and an activation entropy of 17 +/- 7 cal/mol per K. The repressor greatly retards the exchange of imino protons, and the activation energy increases to 38 kcal/mol. There are small changes in the structure of the DNA on forming the complex, with the adenine and thymidine residues becoming more similar in conformation.
我们已经确定了来自大肠杆菌的色氨酸（trp）阻遏物对dA20dT20结构和动力学的影响。通过时间依赖性核Overhauser效应和自旋晶格弛豫时间确定了其结构。胸腺嘧啶残基的脱氧核糖构象接近C3'内型，腺嘌呤残基的构象约为30% C3'内型和70% C2'内型的混合物。糖苷扭转角对于T为-50度，对于A为-60度。滚动为20度，螺旋扭转约为29度。该构象与最近的计算结果一致（Rao, K.和Kollman, P.A.（1985年）《美国化学会志》107, 1507 - 1511）。亚氨基质子交换的速率常数与通常在AT碱基对中发现的相似，活化能为20 +/- 2千卡/摩尔，活化熵为每K 17 +/- 7卡/摩尔。阻遏物极大地延缓了亚氨基质子的交换，活化能增加到38千卡/摩尔。形成复合物时DNA的结构有微小变化，腺嘌呤和胸腺嘧啶残基的构象变得更加相似。
