中药桑椹中RG-I类多糖与肠道多形拟杆菌相互作用机理研究

Pectin is one kind of glycan found extensively from the plant of traditional Chinese medicine. The biological functions are anti-tumor, hypoglycemic, immunoregulation, and improving constipation. RG-I is one of the major types of pectin. Related enzymes have been identified from the dominant phyla of human gut bacterium, which could degrade the specific structure of pectin. However, due to pectins vary in their complex side-chain structure, the interaction between RG-I and Bacteroidetes are poorly understood. Our research found B. thetaiotaomicron could grow on homogeneous glycan FMP-6-S2, which is RG-I type isolated from Mulberry fruit, and high expressed genes of “Polysaccharide utilization locus”. It implied that B. thetaiotaomicron could degrade FMP-6-S2. In addition, FMP-6-S2 could bind with the outer membrane SusD of B. thetaiotaomicron. Based on FMP-6-S2, this project aims to understand the mechanism of interaction between RG-I type glycan and gut B. thetaiotaomicron including: 1) the molecular mechanism of degradation of FMP-6-S2 by B. thetaiotaomicron; 2) the targeting and mechanism of FMP-6-S2 action on B. thetaiotaomicron. Our research will uncover polysaccharide based bioactive compounds of traditional Chinese medicine, how gut bacteria utilize glycan and the molecular mechanism of interaction. Our findings will provide the solid theory foundation for glycan-based new drug development by targeting gut microbiota.

果胶是广泛存在于植物类中药的多糖，具有抗肿瘤、降血糖、免疫调节、改善便秘等生物活性。RG-I类果胶是果胶中主要类型之一，虽然有文献报道人类肠道中的优势菌群拟杆菌具有降解特定结构果胶的相关酶，但由于RG-I复杂多样的支链结构，其与拟杆菌相互作用的机理远未清楚。本项目前期研究发现多形拟杆菌能利用桑椹中RG-I类均一多糖FMP-6-S2，并高表达其基因组上“多糖利用位点”的基因，提示该菌能降解FMP-6-S2；且发现FMP-6-S2能与该菌的外膜蛋白SusD结合。本项目拟以FMP-6-S2为探针，瞄准RG-I多糖与肠道多形拟杆菌相互作用的机理这一科学问题，研究1）多形拟杆菌降解FMP-6-S2的分子机制；2）FMP-6-S2作用于多形拟杆菌的靶向性及其机制。项目实施将有助于阐明基于多糖的中药活性物质基础和肠道菌群如何利用多糖及其相互作用机理，为靶向肠道菌群的聚糖类创新药物研究奠定坚实理论基础。

果胶是广泛存在于植物类中药的多糖，具有抗肿瘤、降血糖、免疫调节、改善便秘等生物活性，RG-I类果胶是果胶中主要类型之一，虽然有文献报道人类肠道中的优势菌群拟杆菌具有降解特定结构果胶的相关酶，但由于RG-I复杂多样的支链结构，其与拟杆菌相互作用的机理远未清楚。因此我们推测多形拟杆菌的基因组上可能还存在其他的果胶降解酶。我们系统阐述了果胶多糖FMP-6-S2是如何被人的肠道多形拟杆菌基因组上的“多糖利用位点PULs”抓取/解链/和最终降解为单糖。简单概括：1）多形拟杆菌的基因组上有4个不连续的多糖利用位点参与了此过程，其中的两个PULs尚未被报道；2）4个多糖利用位点中包含了10个酶和4个多糖结合蛋白，其中的一个surface enzyme 和 surface glycan binding protein是我们新发现的；3）FMP-6-S2的降解产物可以促进肠道内其他拟杆菌和益生菌的生长；4）参与该过程的降解酶类也广泛存在与其他拟杆菌的基因组上。我们的结果进一步完善了肠道拟杆菌代谢果胶类多糖的代谢网络，为靶向性改善肠道菌群提供了理论基础。