糖的多羟基使特异糖苷的化学法合成步骤繁琐；糖苷酶法糖基供体为简单糖类且糖基受体多样，应用潜力巨大。唾液酸末端定位的唾液酸糖链普遍存在于高等生物细胞表面，具有细胞间相互作用、免疫反应、病原体粘附等重要功能；人乳寡糖的70%以上是唾液酸寡糖，在婴幼儿肠道菌群形成、大脑发育及抵抗病原体感染中具有重要作用。我们已从糖酶数据库CAZy Database发掘出了一种新的唾液酸苷酶，以目前报道的最高转化率专一合成了6’-唾液酸基乳糖。本项目拟从该数据库中继续发掘出更多新的转糖基唾液酸苷酶，分子改造提高酶的转糖基活性和区域选择性，拓展酶的底物特异性，并阐释特殊氨基酸位点影响转糖基活性、区域选择性及底物特异性的分子机制。项目完成不仅可获得多种新的糖合成工具酶用于唾液酸糖链和糖苷化合物的合成，而且所阐释的糖苷酶转糖基作用相关的分子机制，也将加深人们对糖苷酶转糖基性质的理解，促进糖苷酶法合成糖苷的研究及应用。

More than one available reactive hydroxyl group of carbohydrates makes chemical synthesis laborious and difficult for application. The glycosidase approach in enzymatic synthesis has better industrial practicality as the simple glycosyl donors and diverse acceptors are used. Sialoglycans with sialic acid occupation of outermost positions are widespread in higher animal cell surface have a variety of important biological functions, such as cell-cell interactions, immune response, pathogen adhesion and so on. More than 70% of human milk oligosaccharides are sialyloligosaccharides which play important roles in gut maturation, brain and cognitive development and supporting resistance to pathogen infection in neonate. We have unearthed a new sialidase from CAZy Database and synthesized 6'-sialyllactose at the highest conversion reported so far. This project intends to discover more new transglycosyl-sialidase from CAZy Database. We will make use of molecular evolution to improve trans-glycosylation activity and regioselectivity of the enzymes, and to expand their substrate specificity. Moreover, we will elucidate the molecular mechanism of effects of specific amino acid sites on trans-glycosylation activity, substrate specificity and regioselectivity. The research will be able to provide a variety of new powerful enzymatic tools for the synthesis of sialoglycans/ sialyloligosaccharides and sialyl-chemicals and the interpretation of the specific amino acid sites affecting transglycosylation, substrate specificity and regioselectivity, which will deepen the understanding of the mechanism of glycosidase transglycosylation and promote the practice of glucosidase synthesis of glygan.