Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei 10617, Taiwan.
International Graduate Program of Molecular Science and Technology, National Taiwan University (NTU-MST), Taipei 10617, Taiwan.
Phys Chem Chem Phys. 2023 Aug 23;25(33):22179-22194. doi: 10.1039/d3cp02530f.
Determining carbohydrate structures, such as their compositions, linkage positions, and in particular the anomers and stereoisomers, is a great challenge. Isomers of different anomers or stereoisomers have the same sequences of chemical bonds, but have different orientations of some chemical bonds which are difficult to be distinguished by mass spectrometry. Collision-induced dissociation (CID) tandem mass spectroscopy (MS/MS) is a widely used technique for characterizing carbohydrate structures. Understanding the carbohydrate dissociation mechanism is important for obtaining the structural information from MS/MS. In this work, we studied the CID mechanism of galactose--acetylgalactosamine (Gal-GalNAc) and glucose--acetylglucosamine (Glc-GlcNAc) disaccharides with 1→3 and 1→4 linkages. For Gal-GalNAc disaccharides, the CID mass spectra of sodium ion adducts show significant difference between the α- and β-anomers of GalNAc at the reducing end, while no difference in the CID mass spectra between two anomers of Glc-GlcNAc disaccharides was found. Quantum chemistry calculations show that for Gal-GalNAc disaccharides, the difference of the dissociation barriers between dehydration and glycosidic bond cleavage is significantly small in the β-anomer compared to that in the α-anomer; while these differences are similar between the α- and β-anomers of Glc-GlcNAc disaccharides. These differences can be attributed to the different orientations of hydroxyl and -acetyl groups located at GalNAc and GlcNAc. The calculation results are consistent with the CID spectra of isotope labelled disaccharides. Our study provides an insight into the CID of 1→3 and 1→4 linked Gal-GalNAc and Glc-GlcNAc disaccharides. This information is useful for determining the anomeric configurations of GalNAc in oligosaccharides.
确定碳水化合物的结构，如组成、连接位置，特别是端基异构体和立体异构体，是一个巨大的挑战。不同端基异构体或立体异构体的异构体具有相同的化学键序列，但某些化学键的方向不同，这很难通过质谱法区分。碰撞诱导解离（CID）串联质谱（MS/MS）是一种广泛用于表征碳水化合物结构的技术。了解碳水化合物的解离机制对于从 MS/MS 获得结构信息非常重要。在这项工作中，我们研究了具有 1→3 和 1→4 键的半乳糖-乙酰半乳糖胺（Gal-GalNAc）和葡萄糖-乙酰葡萄糖胺（Glc-GlcNAc）二糖的 CID 机制。对于 Gal-GalNAc 二糖，钠离子加合物的 CID 质谱在还原端的 GalNAc 的α-和β-端基异构体之间显示出显著差异，而 Glc-GlcNAc 二糖的两个端基异构体的 CID 质谱没有差异。量子化学计算表明，对于 Gal-GalNAc 二糖，与α-端基异构体相比，β-端基异构体中脱水和糖苷键断裂的解离势垒之间的差异显著较小；而 Glc-GlcNAc 二糖的α-和β-端基异构体之间的这些差异相似。这些差异可以归因于位于 GalNAc 和 GlcNAc 上的羟基和-乙酰基的不同取向。计算结果与同位素标记二糖的 CID 谱一致。我们的研究提供了对 1→3 和 1→4 连接的 Gal-GalNAc 和 Glc-GlcNAc 二糖 CID 的深入了解。这些信息对于确定寡糖中 GalNAc 的端基构型有用。
