Mass spectrometry for structural elucidation and sequencing of carbohydrates
Introduction
Carbohydrate, widely distributed in animals, plants and microorganisms, plays an important role in metabolism and structural properties of biological systems. The earliest study for the chemistry of simple sugars was came from Fischer in 1893 [1], and ring structure investigation was reported by Haworth and his colleagues in 1920–1940 [[2], [3], [4]]. Carbohydrates have diverse structures based on different types of building block (i.e. monosaccharide), ring size (i.e. pyranose and furanose), configuration (i.e. α and β), regiochemistry (i.e. different linkage patterns), branching, chain length, repeating units, etc. (Fig. 1A). In addition, other chemical groups, such as sulfate, ferulic acid, acetyl, methoxyl, and so on, might be jointed in the main chain or branches. Due to these unique structure complexity, high-throughput identification and characterization of carbohydrates still remain a big challenge.
Mass spectrometry (MS), with the advantages over high-throughput, high sensitivity and low detection limit, has experienced rapid development in the last decades, and these improvements made it more and more feasible for high-resolution profiling of carbohydrates, yielding accurate mass and structurally informative fragments. Recently, many researches concentrated on mass spectrometric or MS-hybridized approaches in the field of glycomics and glycoproteomics [[5], [6], [7], [8], [9], [10], [11]]. In this review, the latest developments in mass spectrometric technologies that allowed for structural characterization of oligosaccharides and polysaccharides, including the schemes or workflows, compositional monosaccharide, linkage patterns of residues, sequences, degree of polymerization and substitution were summarized. In addition, MS applications in herbal and food glycans analysis, as well as the potential future perspective were also described.
Section snippets
Procedure for MS analysis of carbohydrates
Typically, a mass spectrometer includes an ionization source, an analyzer and a detector, as shown in Fig. 1B. Firstly, ions are generated in an ionization source, followed by separation by the analyzer based on their respective mass-to-charge ratio (m/z), and then recorded by the detector [12]. Among the ion sources, soft ionization techniques, including electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), impart little excess energy and generate intact
Mass spectrometric analysis for carbohydrate structures
According to the nomenclature introduced by Domon and Costello [39], as shown in Fig. 1C, it would be better to explain and understand the details of carbohydrate fragmentation patterns. Specifically, three major types of product ions would be observed in the fragmentation of oligosaccharides. Obviously, A-/X-ions produced by an individual sugar residue could provide linkage information. On the other hand, B-/Y- and C-/Z-product ions are generated by glycosidic bond cleavage of adjacent sugar
Applications in herbal and food polysaccharide analysis
Herein, examples of applications were given excluded the well-reviewed biological O- and N-linked glycans from glycoconjugates. As mentioned previously, considering the high molecular weight, polysaccharides were usually degraded to oligosaccharides prior to be subjected to MS analysis (Table 3). In early studies, CE-LIF and CE-ESI-MSn were shown to be powerful in separation and identification of 9-aminopyrene-1,4,6-trisulfonate (APTS)-derivatized oligosaccharides from plant polysaccharides,
Conclusions and future perspectives/challenges
Carbohydrates are the most abundant and diverse class of organic compounds in nature, and understanding their structures is still a challenge due to their complexities. The developments of high-resolution mass spectrometry technologies made it possible to rapid profiling of carbohydrates structures through accurate mass and diagnostic fragments. However, there was still limited progress in quantitative analysis of carbohydrate using mass spectroscopy, and some of these were relatively
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The research was partially funded by grants from the National Natural Science Foundation of China (No. 81673389), the National Key R&D Program of China (2019YFC1711300), the Science and Technology Development Fund, Macau SAR (File no. 034/2017/A1 and 0017/2019/AKP), the Key Area Research and Development Program of Guangdong Province (File no. 2020B1111110006), Guangzhou Municipal Science and Technology Bureau (201807010051) and the University of Macau (File no. MYRG2018-00083-ICMS/
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