ABSTRACT
Glucansucrases are expressed by lactic acid bacteria and classified as glycoside hydrolase (GH) enzymes of family 70 according to the carbohydrate-active enzyme database CAZy (Monchois et al., 1999; Henrissat, 1991). Even they are structurally related to glycosidases; their main reaction products are glucan polymers, not hydrolysis. Thus in the EC-classification system, glucansucrases are classified in EC 2.4.1.5 (dextransucrase) and EC 2.4.1.140 (alternansucrase). So far, no 3D structure of glucansucrases has been published. However, from sequence alignments of the primary structure and structural comparison with GH-13 (α-amylase) enzymes, it can be concluded that glucansucrases are organized in a (α/β)8barrel, where the N-terminal, variable region of different length, is followed by a conserved catalytic domain and a C-terminal glucan-binding domain (van Hijum et al., 2006; McGregor et al., 1996). This prediction was confirmed by Dijkstra et al. (personal communication), who solved a unpublished crystal structure of GTF180, a glucansucrase of Leuconostoc mesenteroides 180 on a congress in Braunschweig.Glucansucrases are relevant enzymes for industrial applications. The production of the polysaccharide dextran (α-1,6-glucan) by Leuconostoc mesenteroides is one example. Such polymers are
used in the food sector as additives for dyes and in healthcare (Lacaze et al., 2007; Coviello et al., 2006). Variants and differences in glycosidic linkage type, degree, and type of branching and molecular mass of glucans yield different structural and functional properties.
