Levan蔗糖酶及其在Levan果聚糖合成中的应用

Application of levansucrase in levan synthesis-A review

摘要:

摘要:Levan果聚糖是一类分子中含有大量β-(2，6)果糖苷键主链和少量β-(2，1)果糖苷键支链的聚糖。部分微生物来源的Levan果聚糖具有抗肿瘤、抗糖尿病、免疫增强、降血脂等重要的生物活性，在医药和功能食品方面具有巨大的应用潜能。由于微生物发酵液提取法产量相对较低，而化学法合成过程繁琐，Levan果聚糖的酶法合成备受关注。Levan 蔗糖酶(Levansucrase，EC 2.4.1.10)属于糖苷酶家族GH68，是一类β-螺旋桨家族蛋白，其催化糖类合成遵循non-Leloir糖基转移酶机制，以蔗糖为底物转果糖基合成Levan果聚糖。部分微生物Levan蔗糖酶的分子结构及基因的表达调控已经得到阐明，Levan果聚糖的酶法合成得到广泛研究。本文综述了Levan蔗糖酶的催化机制、酶分子结构、酶基因表达调控以及酶在合成Levan果聚糖中的应用，以促进微生物Levan蔗糖酶及Levan果聚糖的研究和应用。

Abstract:

Abstract:Levan is a fructan mainly linked by β-(2，6)-glycosidic bonds with some β-(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 betapropeller 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．