Characterisation of insoluble α-1,3-/α-1,6 mixed linkage glucan produced in addition to soluble α-1,6-linked dextran by glucansucrase (DEX-N) from Leuconostoc citreum ABK-1

Glucansucrases catalyse the formation of glucans from sucrose. The glucansucrase-encoding gene from Leuconostoc citreum ABK-1, dex-N, was successfully cloned and expressed in E. coli BL21 Star (DE3). DEX-N produces 2 types of glucans: soluble (S-dextran) and insoluble (I-glucan) glucans. The S-dextran was determined to be ca. 10 kDa in size and contained >90% α-1,6 linkages; along with its water solubility, this is similar to commercial dextran. On the other hand, I-glucan was water-insoluble, harbouring a block-wise pattern of α-1,3 and α-1,6 linkages in its structure. Notably, the FTIR and powder X-ray diffraction pattern of I-glucan exhibited a combination of features found in α-1,6-linked dextran and α-1,3-linked mutan. Although both I-glucan and mutan are insoluble glucans, their physical characteristics are notably dissimilar.