Abstract
Glucansucrase enzymes from lactic acid bacteria are receiving strong interest because of their wide range of gluco-oligosaccharide and polysaccharide products from sucrose, some of which have prebiotic potential. Glucansucrases GtfA and Gtf180 from Lactobacillus reuteri strains are known to convert sucrose into α-glucans with different types of linkages, but also to use other molecules as acceptor substrates. Here we report that incubation of (N-terminally truncated versions of) these enzymes with lactose plus sucrose resulted in synthesis of at least 5 glucosylated lactose products of a degree of polymerization (DP) of 3–4. Only glucansucrase Gtf180-ΔN also produced larger lactose-based oligosaccharides (up to DP9). Structural characterization of the glucosylated lactose products DP3-4 revealed glycosidic bonds other than (α1→4)/(α1→6) typical for GtfA-ΔN and (α1→3)/(α1→6) typical for Gtf180-ΔN: Both GtfA-ΔN and Gtf180-ΔN now introduced a glucosyl residue (α1→3)- or (α1→4)-linked to the non-reducing galactose unit of lactose. Both enzymes also were able to introduce a glucosyl residue (α1→2)-linked to the reducing glucose unit of lactose. These lactose derived oligosaccharides potentially are interesting prebiotic compounds.
Highlights
Glucansucrase enzymes (Gtfs) of glycoside hydrolase family 70 (GH70) are extracellular enzymes that only have been identified in lactic acid bacteria (LAB) [1]
Initial reactions were performed with sucrose and lactose concentrations of 0.5 M, at 37 C and pH 4.7 during 24 h, which is the catalytic optimum of the Gtf180-DN and GtfA-DN enzymes for a-glucan synthesis from sucrose [1,2]
At least five glucosylated lactose products with DP3 and DP4 were synthesized by GtfA-DN and Gtf180-DN and structurally characterized
Summary
Glucansucrase enzymes (Gtfs) of glycoside hydrolase family 70 (GH70) are extracellular enzymes that only have been identified in lactic acid bacteria (LAB) [1]. They catalyze three types of reactions, depending on the nature of the acceptor substrate: hydrolysis when water is used as acceptor substrate, polymerization when the growing glucan chain is used as acceptor, and transglycosylation when other compounds including oligosaccharides are used as acceptor [2]. The currently known diversity of glucansucrases is capable of synthesizing a-glucans with all the possible glycosidic linkage types [(a1/2), (a1/3), (a1/4) and (a1/6)] They are classified into dextran-, mutan-, reuteran-, and alternansucrases based on the (dominant) linkage type(s) in their products [2e5]. In case of Gtf180-DN longer oligosaccharides were observed
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