Department of Molecular and Experimental Medicine, The Scripps Research Institute , La Jolla, California 92037, United States.
Department of Chemistry, The Scripps Research Institute , La Jolla, California 92037, United States.
J Am Chem Soc. 2016 Jun 22;138(24):7636-48. doi: 10.1021/jacs.6b02879. Epub 2016 Jun 14.
Interactions between proteins and carbohydrates are ubiquitous in biology. Therefore, understanding the factors that determine their affinity and selectivity are correspondingly important. Herein, we have determined the relative strengths of intramolecular interactions between a series of monosaccharides and an aromatic ring close to the glycosylation site in an N-glycoprotein host. We employed the enhanced aromatic sequon, a structural motif found in the reverse turns of some N-glycoproteins, to facilitate face-to-face monosaccharide-aromatic interactions. A protein host was used because the dependence of the folding energetics on the identity of the monosaccharide can be accurately measured to assess the strength of the carbohydrate-aromatic interaction. Our data demonstrate that the carbohydrate-aromatic interaction strengths are moderately affected by changes in the stereochemistry and identity of the substituents on the pyranose rings of the sugars. Galactose seems to make the weakest and allose the strongest sugar-aromatic interactions, with glucose, N-acetylglucosamine (GlcNAc) and mannose in between. The NMR solution structures of several of the monosaccharide-containing N-glycoproteins were solved to further understand the origins of the similarities and differences between the monosaccharide-aromatic interaction energies. Peracetylation of the monosaccharides substantially increases the strength of the sugar-aromatic interaction in the context of our N-glycoprotein host. Finally, we discuss our results in light of recent literature regarding the contribution of electrostatics to CH-π interactions and speculate on what our observations imply about the absolute conservation of GlcNAc as the monosaccharide through which N-linked glycans are attached to glycoproteins in eukaryotes.
蛋白质和碳水化合物之间的相互作用在生物学中普遍存在。因此，了解决定它们亲和力和选择性的因素相应地非常重要。在这里，我们确定了一系列单糖与接近 N-糖蛋白宿主中糖基化位点的芳环之间的分子内相互作用的相对强度。我们利用增强的芳香序列基序，该基序存在于一些 N-糖蛋白的反向转弯中，促进单糖-芳基相互作用。之所以使用蛋白质宿主，是因为可以准确测量折叠能与单糖身份的依赖性，以评估碳水化合物-芳基相互作用的强度。我们的数据表明，糖-芳基相互作用强度受到糖吡喃环取代基的立体化学和身份变化的适度影响。半乳糖似乎与所有糖形成最弱的糖-芳基相互作用，而葡萄糖、N-乙酰葡萄糖胺（GlcNAc）和甘露糖则介于两者之间。解决了几种含有单糖的 N-糖蛋白的 NMR 溶液结构，以进一步了解单糖-芳基相互作用能之间的相似性和差异的起源。在我们的 N-糖蛋白宿主中，单糖的全乙酰化大大增加了糖-芳基相互作用的强度。最后，我们根据最近关于静电对 CH-π 相互作用贡献的文献讨论我们的结果，并推测我们的观察结果对 GlcNAc 作为通过 N-连接聚糖附着在真核生物中糖蛋白上的单糖的绝对保守性意味着什么。
