The levansucrase and inulosucrase enzymes of Lactobacillus reuteri 121 catalyse processive and non-processive transglycosylation reactions
article
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 β(2→6)- versus β(2[1)-glycosidic-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 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 FTF 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 FTF 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. © 2006 SGM. Molecular Sequence Numbers: GENBANK: AF459437, AF465251; Chemicals / CAS: amino acid, 65072-01-7; fructose oligosaccharide, 88385-81-3; glucose, 50-99-7, 84778-64-3; inulin, 9005-80-5; levan, 50815-13-9, 9013-95-0; levansucrase, 9030-17-5; sucrase, 37288-39-4; Fructans; Hexosyltransferases, EC 2.4.1.-; Idolax; inulosucrase, EC 2.4.1.9; levan, 9013-95-0; levansucrase, EC 2.4.1.10; Oligosaccharides; Sucrose, 57-50-1
Topics
Food technologyamino acidbacterial enzymecarbohydrate binding proteinfructose oligosaccharideglucoseinulininulosucraselevanlevansucrasepolymersucraseunclassified drugamino acid sequencearticlecatalysiscontrolled studyenzyme activityenzyme bindingenzyme glycosylationenzyme mechanismenzyme specificityenzyme substrateenzyme synthesisgenetic conservationgenetic similarityglycosidationLactobacillus reuterinonhumannucleotide sequencepriority journalprotein hydrolysisBinding SitesChromatography, Ion ExchangeChromatography, Thin LayerFructansGlycosylationHexosyltransferasesLactobacillus reuteriOligosaccharidesSubstrate SpecificitySucroseBacteria (microorganisms)Lactobacillus reuteri
TNO Identifier
239193
ISSN
13500872
Source
Microbiology, 152(4), pp. 1187-1196.
Pages
1187-1196
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