Novel oligosaccharides synthesized from sucrose donor and cellobiose acceptor by alternansucrase Original Research Article

Cellobiose was tested as acceptor in the reaction catalyzed by alternansucrase (EC 2.4.1.140) from Leuconostoc mesenteroides NRRL B-23192. The oligosaccharides synthesized were compared to those obtained with dextransucrase from L. mesenteroides NRRL B-512F. With alternansucrase and dextransucrase, overall oligosaccharide synthesis yield reached 30 and 14%, respectively, showing that alternansucrase is more efficient than dextransucrase for cellobiose glucosylation. Interestingly, alternansucrase produced a series of oligosaccharides from cellobiose. Their structure was determined by mass spectrometry and {13C–1H} NMR spectroscopy. Two trisaccharides are first produced: α-d-glucopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-d-glucopyranose (compound A) and α-d-glucopyranosyl-(1→6)-β-d-glucopyranosyl-(1→4)-d-glucopyranose (compound B). Then, compound B can in turn be glucosylated leading to the synthesis of a tetrasaccharide with an additional α-(1→6) linkage at the non-reducing end (compound D). The presence of the α-(1→3) linkage occurred only in the pentasaccharides (compounds C1 and C2) formed from tetrasaccharide D. Compounds B, C1, C2 and D were never described before. They were produced efficiently only by alternansucrase. Their presence emphasizes the difference existing in the acceptor reaction selectivity of the various glucansucrases.