Astragalus polysaccharides are the most immunoregulatory active and abundant substances in Astragalus, with anti-tumor, anti-viral, and immune-promoting biological activities. They have been widely used in clinical practice. Previous studies have found that Astragalus polysaccharides are mainly composed of two different polysaccharides, APS-Ⅰ (> 2 000 kDa) and APS-Ⅱ (10 kDa), with APS-Ⅱ (10 kDa) being the most active component of Astragalus polysaccharides. We used α-1, 4-glucan endo-hydrolysis enzyme to degrade APS-Ⅱ into oligosaccharides, and screened the immune activity of oligosaccharides in vitro. We found that the overall immune activity of 2-9 oligosaccharides was low, while the immune activity of 10-14 oligosaccharides was strong, and the activity was better than that of untreated APS-Ⅱ. To investigate the key structural features of APS-Ⅱ oligosaccharides that play a role in immune activity, we used MALDI-TOF-MS biochemical mass spectrometry and high-resolution mass spectrometry instrument ESI-Q Exactive-MS to analyze the APS enzymatic oligosaccharides. By comparing, we found that 10-14 oligosaccharides contain 1→4 and 1→6 branched structures with coexisting linkages, suggesting that 1→4 and 1→6 linkages in branched structures are key structural features that play a role in the immune activity of APS-Ⅱ, laying a theoretical foundation for the structure-activity relationship of Astragalus polysaccharides and oligosaccharides.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |