Zhang Wenhui, Turney Toby, Meredith Reagan, Pan Qingfeng, Sernau Luke, Wang Xiaocong, Hu Xiaosong, Woods Robert J, Carmichael Ian, Serianni Anthony S
Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556-5670, United States.
Omicron Biochemicals Inc. , South Bend, Indiana 46617-2701, United States.
J Phys Chem B. 2017 Apr 13;121(14):3042-3058. doi: 10.1021/acs.jpcb.7b02252. Epub 2017 Mar 30.
Twelve disaccharides containing β-(1→4) linkages and displaying systematic structural variations in the vicinity of these linkages were selectively labeled with C to facilitate measurements of multiple NMR spin-spin (scalar; J) coupling constants (J and J values) across their O-glycosidic linkages. Ensembles of spin-couplings (J, J, J) sensitive to the two linkage torsion angles, phi (ϕ) and psi (ψ), were analyzed by using parametrized equations obtained from density functional theory (DFT) calculations, Fredholm theory, and circular statistics to calculate experiment-based rotamer populations for ϕ and ψ in each disaccharide. With the statistical program MA'AT, torsion angles ϕ and ψ were modeled as a single von Mises distribution, which yielded two parameters, the mean position and the circular standard deviation (CSD) for each angle. The NMR-derived rotamer populations were compared to those obtained from 1 μs aqueous molecular dynamics (MD) simulations and crystallographic database statistical analyses. Conformer populations obtained exclusively from the MA'AT treatment of redundant J-couplings were in very good agreement with those obtained from the MD simulations, providing evidence that conformational populations can be determined by NMR for mobile molecular elements such as O-glycosidic linkages with minimal input from theory. The approach also provides an experimental means to validate the conformational preferences predicted from MD simulations. The conformational behaviors of ϕ in the 12 disaccharides were very similar, but those of ψ varied significantly, allowing a classification of the 12 disaccharides based on preferred linkage conformation in solution.
十二个含有β-(1→4)键且在这些键附近呈现系统结构变化的二糖被选择性地用碳进行标记，以利于测量其O-糖苷键上多个核磁共振自旋-自旋（标量；J）耦合常数（J和J值）。通过使用从密度泛函理论（DFT）计算、弗雷德霍姆理论和循环统计获得的参数化方程，分析了对两个键扭转角φ（ϕ）和ψ（ψ）敏感的自旋耦合集合（J、J、J），以计算每个二糖中ϕ和ψ基于实验的旋转异构体群体。使用统计程序MA'AT，将扭转角ϕ和ψ建模为单个冯·米塞斯分布，这为每个角度产生了两个参数，即平均位置和循环标准差（CSD）。将核磁共振衍生的旋转异构体群体与从1微秒的水溶液分子动力学（MD）模拟和晶体学数据库统计分析中获得的群体进行比较。仅通过对冗余J耦合进行MA'AT处理获得的构象群体与从MD模拟中获得的群体非常吻合，这表明对于诸如O-糖苷键等可移动分子元件，无需理论的大量输入就可以通过核磁共振确定构象群体。该方法还提供了一种实验手段来验证从MD模拟预测的构象偏好。这12个二糖中ϕ的构象行为非常相似，但ψ的构象行为差异很大，从而可以根据溶液中优选的键构象对这12个二糖进行分类。
