电喷雾质谱在寡糖序列分析中的应用

摘要

选取具有不同结构特征的N­糖链、硫酸软骨素寡糖、人乳寡糖以及海洋来源的壳寡糖、褐藻胶寡糖、卡拉胶寡糖和硫酸岩藻寡糖等，对电喷雾质谱在寡糖的主链序列、分支位点、硫酸基取代位置确定、单糖组成和聚合度分析等方面的应用技术及碎片离子的断裂规律进行了总结。根据相邻同类碎片离子之间的质荷比差值可初步判断寡糖的单糖组成类型；通过与色谱分离技术联用或衍生化方法可提高寡糖的分辨率和离子化效率，并测得寡糖的分子量及聚合度；借助串联质谱及对寡糖还原端的特异性标记，可获得寡糖的还原端残基和部分序列信息；根据寡糖产生的特征碎片离子及其丰度大小可判断残基的特定位置和类型。另外，寡糖的分支通常作为一个整体发生糖苷键断裂或产生D离子，据此可判断分支点的位置；根据硫酸寡糖产生的特异性跨环断裂碎片，可以确定硫酸基的连接位置。这些规律和方法的总结为未知寡糖的结构和序列的分析提供了启发和指导。%Analysis of oligosaccharide structure and sequence plays a significant role in unravelling the biolo­ gical function of glycoconjugates. Electrospray ionization mass spectrometry( ESI­MS) is an important tool for the qualitative and quantitative analysis of oligosaccharides with high sensitivity, high precision and high speed. Some oligosaccharides with different structural characteristics, such as N­glycans, chondroitin sulfate oligosaccharides, human milk oligosaccharides, chitooligosaccharide, alginate oligosaccharides, carrageenan oligosaccharides and sulfated fucan oligosaccharides are discussed in this paper. The application techniques of ESI­MS and fragmentation rule of oligosaccharides in the sequence analysis of the main chain, branch sites, substitution positions of sulfate groups, as well as the monosaccharide composition and the degree of polymeri­ zation are summarized. The types of monosaccharide composition can be obtained primarily based on the adja­ cent m/z difference of B/C fragment ions. The resolution and ionization efficiency of oligosaccharides can be improved by combination with chromatography separation techniques or derivatization methods, and then the molecular weight and degree of polymerization of oligosaccharides can be measured. The information of redu­ cing residue and partial sequence of oligosaccharides can be obtained by means of tandem mass spectrometry and characterized derivatization of the reducing end. The types and particular locations of residues can be de­ termined according to their specific fragment ions and abundance. In addition, the branches of oligosaccharide usually occur glycoside bond breakage as a unit or produce D ions, which can be used to determine the branch points. The sulfate groups in different sites can be obtained by their specific cross­ring fragments. The summa­ rization of fragmentation rule of oligosaccharides in ESI­MS provides a guidance to the structure and sequence analysis of unknown oligosaccharides.