Characterization of a 4,6‑α‑glucanotransferase from Lactobacillus reuteri E81 and production of malto-oligosaccharides with immune-modulatory roles

A wide number of Lactic Acid Bacteria (LAB) species produce α-glucans with their ability to synthesize glucansucrases (GS) which use sucrose as substrate for the glucan production. Recently another group of enzymes in LAB gained special interest for their ability to produce α-glucans targeting the substrates containing α1-4-linkages and synthesizing new (α1-6) or (α1-3)–linkages as α‑glucanotransferases. In this study, a putative 4,6‑α‑glucanotransferase (GTFB) from sourdough isolate Lactobacillus reuteri E81 was identified and expressed in Escherichia coli. The biochemical characterization of the GTFB-E81 confirmed its function as it cleaved the α1-4-linkages in different substrates and produced new gluco-oligomers/polymers containing α1-6 linkages together with the α1-4-linkages detected by NMR analysis. GTFB-E81 produced malto-oligosaccharides targeting maltose and maltoheptaose as substrates with up to DP 8 detected by TLC and ESI-MS/MS analysis. The functional roles of these malto-oligosaccharides were determined by testing their immune-modulatory functions in HT29 cells and they triggered the production of anti-inflammatory 1L-4 and pro-inflammatory IL-12 cytokines.