Kessler H, Bats J W, Wagner K, Will M
Biopolymers. 1989 Jan;28(1):385-95. doi: 10.1002/bip.360280136.
The strategy and tactics of conformational analysis of cyclic peptides in solution is demonstrated by the example of cyclo(-D-Pro-Phe-Thr-Phe-Trp-Phe-). Spin-locked experiments like rotating frame nuclear Overhauser enhancement spectroscopy (ROESY), ROTO, and TOCSY are successfully applied to assign all proton signals and to obtain distance information. A crude conformational model was built using the nmr data. This starting model was refined by restrained molecular dynamics (MD) calculations using ROE derived distances and fixed bond angles as determined from homo- and heteronuclear coupling constants. To mimic the solvent and to reduce artifacts in an in vacuo calculation the charges of the solvent-exposed NH protons were gradually reduced according to the temperature gradients. The thus obtained "conformation" (mean of a 40 ps MD trajectory) shows very close similarity to x-ray structures in an orthorhombic and in two monoclinic crystal modifications of the same compound. The main difference is the breaking of an intermolecular hydrogen bond of the threonine hydroxyl group on dissolution of the crystal and forming an intramolecular hydrogen bond in solution.
以环（-D-脯氨酸-苯丙氨酸-苏氨酸-苯丙氨酸-色氨酸-苯丙氨酸-）为例，展示了溶液中环肽构象分析的策略和策略。自旋锁定实验，如旋转框架核Overhauser增强光谱（ROESY）、ROTO和TOCSY，成功地用于确定所有质子信号并获得距离信息。利用核磁共振数据构建了一个粗略的构象模型。该初始模型通过受限分子动力学（MD）计算进行优化，使用从ROE得出的距离和由同核和异核耦合常数确定的固定键角。为了模拟溶剂并减少真空计算中的伪影，根据温度梯度逐渐降低暴露于溶剂的NH质子的电荷。由此获得的“构象”（40 ps MD轨迹的平均值）与同一化合物在正交晶系和两种单斜晶系晶体变体中的X射线结构非常相似。主要区别在于晶体溶解时苏氨酸羟基的分子间氢键断裂，在溶液中形成分子内氢键。
