RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
J Phys Chem B. 2012 Jul 26;116(29):8504-12. doi: 10.1021/jp212550z. Epub 2012 May 2.
The introduction of bisecting GlcNAc and core fucosylation in N-glycans is essential for fine functional regulation of glycoproteins. In this paper, the effect of these modifications on the conformational properties of N-glycans is examined at the atomic level by performing replica-exchange molecular dynamics (REMD) simulations. We simulate four biantennary complex-type N-glycans, namely, unmodified, two single-substituted with either bisecting GlcNAc or core fucose, and disubstituted forms. By using REMD as an enhanced sampling technique, five distinct conformers in solution, each of which is characterized by its local orientation of the Manα1-6Man glycosidic linkage, are observed for all four N-glycans. The chemical modifications significantly change their conformational equilibria. The number of major conformers is reduced from five to two and from five to four upon the introduction of bisecting GlcNAc and core fucosylation, respectively. The population change is attributed to specific inter-residue hydrogen bonds, including water-mediated ones. The experimental NMR data, including nuclear Overhauser enhancement and scalar J-coupling constants, are well reproduced taking the multiple conformers into account. Our structural model supports the concept of "conformer selection", which emphasizes the conformational flexibility of N-glycans in protein-glycan interactions.
双触角型 GlcNAc 及核心岩藻糖基化的引入对于糖蛋白的精细功能调控至关重要。在本文中，通过进行复制交换分子动力学（REMD）模拟，从原子水平研究了这些修饰对 N-糖链构象特性的影响。我们模拟了四种双天线复合型 N-糖链，即未修饰、两种单取代（分别带有双触角型 GlcNAc 或核心岩藻糖）和两种双取代形式。通过使用 REMD 作为增强采样技术，我们观察到所有四种 N-糖链在溶液中存在五种不同的构象，每种构象的特征是其 Manα1-6Man 糖苷键的局部取向。化学修饰显著改变了它们的构象平衡。引入双触角型 GlcNAc 和核心岩藻糖基化后，主要构象的数量分别从五个减少到两个和从五个减少到四个。这种构象的变化归因于特定的残基间氢键，包括水介导的氢键。考虑到多种构象，实验 NMR 数据（包括核 Overhauser 增强和标量 J 耦合常数）得到了很好的重现。我们的结构模型支持“构象选择”的概念，该概念强调了 N-糖链在糖蛋白相互作用中的构象灵活性。
