[Application of levansucrase in levan synthesis--a review]

Levan is a fructan mainly linked by beta-(2,6)-glycosidic bonds with some beta-(2,1)-linked branch chains. Some microbial levan exhibit biological activities such as antitumor, antidiabetic and immunostimulating activities. hypolipidemic effect, and function as prebiotics, which has a wide and potential application in the pharmaceutical and food industry. Because of low extraction yields from microbial fermentation and a very complex process for chemical synthesis of levan, enzymatic synthesis of levan has attracted tremendous interest. Levansucrase (EC 2. 4. 1. 10), a beta-propeller protein belonging to the glycoside hydrolase family 68 (GH68) with reaction mechanism of non-Leloir glycosyltransferase, catalyzes the synthesis of levan by transferring the fructosyl group of non-activated sucrose into the fructan chain. The molecular structure and regulation of gene expression of some microbial levansucrases have been elucidated. Meanwhile, the enzymatic synthesis of levan by levansucrase is widely studied. In this review, catalytic mechanism of levansucrase, molecular structure and regulation of gene expression of some microbial levansucrases, and the application of levansucrases in enzymatic synthesis of levan were summarized.