2'-岩藻糖基乳糖的酶法合成研究进展和展望

Enzymatic synthesis of 2'-fucosyllactose:advances and perspectives

人乳寡糖(human milk oligosaccharides,HMOs)是人乳中一类结构复杂、非消化性的碳水化合物。2'-岩藻糖基乳糖(2'-fucosyllactose,2'-FL)是人乳中含量最高的寡糖,也是最早被FDA和欧盟批准可添加到婴幼儿奶粉、膳食补充剂以及医疗食品中的HMOs之一。2'-FL具有调节肠道菌群、抵抗病原菌的黏附、免疫调节及促进神经系统发育和修复等多种功能活性。2'-FL的主要合成方法有化学合成法、全细胞合成法及酶催化合成法。全细胞合成法是当前工业上生产2'-FL的主要方法,降低L-岩藻糖的成本、调节合成途径中鸟苷二磷酸-L-岩藻糖(GDP-岩藻糖)的水平与菌体生长之间的平衡、发掘新型高活性的α-1,2-岩藻糖基转移酶是降低全细胞合成2'-FL成本的关键。2'-FL的合成途径在一些更为安全表达宿主(如无抗生素大肠杆菌、枯草芽孢杆菌和酵母菌等)中的构建也面临着挑战。本文重点综述了2'-FL酶法合成的研究现状,利用α-1,2-岩藻糖基转移酶合成2'-FL专一性好,但所需糖基供体GDP-岩藻糖成本较高;利用α-L-岩藻糖苷酶的转糖苷活性也可以合成2'-FL,α-L-岩藻糖苷酶来源广泛,易获得,稳定性好,可利用天然底物作为糖基供体。将α-L-岩藻糖苷酶应用于2'-FL合成的关键在于高效的转糖苷酶以及天然、经济的岩藻糖基供体的发掘。酶法合成将来有望成为工业上生产2'-FL的方法。

Human milk oligosaccharides(HMOs)constitute a unique group of endogenous indigestible carbohydrates in human breast milk.HMOs play a crucial role in infant health and growth.As the most abundant HMO,2'-fucosyllactose(Fucα1,2Galβ1,4Glc,2'-FL)has been approved for infant formulas,dietary supplements and medical foods in the United States and European Union.2'-FL has been synthesized by chemical,enzymatic synthesis and cell factory approaches,and currently mainly produced by cell factory approach.The crucial factors for 2'-FL production are the reduction of the cost of L-fucose,the discovery of novelα1,2-fucosyltransferases,and the maintenance of the balance between intracellular GDP-L-fucose level and the growth of engineering strain.Also,the construction of antibiotic-free system(such as antibiotic-free Escherichia coli,Bacillus subtilis and Saccharomyces cerevisiae)is still a challenge for the synthesis of 2'-FL.In this review,the research progress of enzymatic synthesis of 2'-FL was particularly presented.2'-FL could be enzymatically synthesized usingα-1,2-fucosyltransferases orα-L-fucosidases.α-1,2-Fucosyltransferases catalyze the transformation of a fucose from a GDP-L-fucose to a lactose.The main disadvantage for 2'-FL synthesis by fucosyltransferase is the requirement for an expensive nucleotide donor.Also,α-L-fucosidases have been studied extensively since they catalyze the synthesis of 2'-FL through a transglycosylation reaction and often possess a higher availability and activity,in comparison with fucosyltransferases.The discovery of efficient transfucosidases and the availability of appropriate,fucosylated donor substrates will promote the application ofα-L-fucosidases in the synthesis of 2'-FL.In the near future,enzymatic synthesis is expected to become a method for industrial production of 2'-FL.