The levansucrase and inulosucrase enzymes of Lactobacillus reuteri 121 catalyse processive and non-processive transglycosylation reactions
The levansucrase and inulosucrase enzymes of Lactobacillus reuteri 121 catalyse processive and non-processive transglycosylation reactions
复制标题
DOI：
10.1099/mic.0.28484-0
复制
发表时间：
2006-04-01
期刊：
影响因子：
2.8
通讯作者：
Dijkhuizen, L
中科院分区：
文献类型：
--
作者：
Ozimek, LK;Kralj, S;Dijkhuizen, L
细菌果糖转移酶（FTF）酶从蔗糖合成果糖聚合物。根据受体的性质，FTFs催化两种不同的反应，导致：(i)转糖基化，当生长的果聚糖链（聚合）时，或单糖和低聚糖（寡糖合成），被用作受体底物；（ii）水解，以水为受体。罗伊氏乳杆菌121左旋蔗糖酶（Lev）和菊糖酶（Inu）在氨基酸序列水平上密切相关（相似度为86%）。此外，已知参与催化和/或蔗糖结合的8个氨基酸残基是完全保守的。然而，这些酶在其反应和产物特异性上存在显著差异，即β(2 -> - 6)-与β(2 -> - 1)-糖键特异性（分别导致levan和菊糖的合成），以及水解与转糖基化活性的比例[分别导致葡萄糖和低聚果糖(FOSs)/聚合物的合成]。作者报告了罗伊氏杆菌121 Lev和Inu酶从蔗糖和相关低聚糖底物合成的转糖基化反应产物的详细表征。Lev主要将蔗糖转化为大的levan聚合物（过程反应），而Inu主要合成一系列菊糖型FOSs（非过程反应）。有趣的是，这两种IFTF酶也能够利用各种菊糖型FOSs（1-酮糖、1,1-糖糖和1,1,1-酮糖糖）作为底物，催化歧化反应；据我们所知，还没有关于细菌IFTF酶的报道。基于这些数据，我们提出了两种罗伊氏杆菌121 FTF酶中糖结合亚位的组织模型。该模型还解释了酶的催化机制，以及它们的产物特异性差异。
Bacterial fructosyltransferase (FTF) enzymes synthesize fructan polymers from sucrose. FTFs catalyse two different reactions, depending on the nature of the acceptor, resulting in: (i) transglycosylation, when the growing fructan chain (polymerization), or mono- and oligosaccharides (oligosaccharide synthesis), are used as the acceptor substrate; (ii) hydrolysis, when water is used as the acceptor. Lactobacillus reuteri 121 levansucrase (Lev) and inulosucrase (Inu) enzymes are closely related at the amino acid sequence level (86 % similarity). Also, the eight amino acid residues known to be involved in catalysis and/or sucrose binding are completely conserved. Nevertheless, these enzymes differ markedly in their reaction and product specificities, i.e. in beta(2 -> 6)-versus beta(2 -> 1)-glycosic-bond specificity (resulting in levan and inulin synthesis, respectively), and in the ratio of hydrolysis versus transglycosylation activities [resulting in glucose and fructooligosaccharides (FOSs)/polymer synthesis, respectively]. The authors report a detailed characterization of the transglycosylation reaction products synthesized by the Lb. reuteri 121 Lev and Inu enzymes from sucrose and related oligosaccharide substrates. Lev mainly converted sucrose into a large levan polymer (processive reaction), whereas Inu synthesized mainly a broad range of FOSs of the inulin type (non-processive reaction). Interestingly, the two IFTF enzymes were also able to utilize various inulin-type FOSs (1-kestose,1,1-nystose and 1,1,1-kestopentaose) as substrates, catalysing a disproportionation reaction; to the best of our knowledge, this has not been reported for bacterial IFTF enzymes. Based on these data, a model is proposed for the organization of the sugar-binding subsites in the two Lb. reuteri 121 FTF enzymes. This model also explains the catalytic mechanism of the enzymes, and differences in their product specificities.