The glucansucrase of Lactobacillus reuteri 180 catalyzes the synthesis of a diversity of α-glucans out of sucrose. The wild type enzyme synthesizes dextran-like α-glucans containing α(1→6) and α(1→3) glycosidic linkages in presence of sucrose. Instead, the GTF180-ΔN mutant L940W is unable to form (α1→3) linkages in its products. The enzyme synthesizes mainly linear isomalto-oligosaccharides (IMOs) and a minor amount of α-glucans (up to 6.3MDa) using sucrose as a substrate. The products contain α(1→6) glycosidic linkages only. The product size is relatively small compared with the wild type enzyme. Enzyme mutations of Leu940 in domain B significantly changed the linkage specificity, reaction specificity, and activity.