Abstract:

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 novel α1,2-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 using α-1,2-fucosyltransferases or α-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 of α-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.

Key words: human milk oligosaccharides, 2'-fucosyllactose, GDP-L-fucose, enzymatic synthesis, α-L-fucosidase, enzyme engineering

摘要：

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。

关键词: 人乳寡糖, 2'-岩藻糖基乳糖, GDP-岩藻糖, 酶法合成, α-L-岩藻糖苷酶, 酶工程