Processivity of dextransucrases synthesizing very-high-molar-mass dextran is mediated by sugar-binding pockets in domain V.

The dextransucrase DSR-OK from the Gram-positive bacterium DSM17330 produces a dextran of the highest molar mass reported to date (∼10 g/mol). In this study, we selected a recombinant form, DSR-OKΔ1, to identify molecular determinants involved in the sugar polymerization mechanism and that confer its ability to produce a very-high-molar-mass polymer. In domain V of DSR-OK, we identified seven putative sugar-binding pockets characteristic of glycoside hydrolase 70 (GH70) glucansucrases that are known to be involved in glucan binding.

Characterization of the First α-(1→3) Branching Sucrases of the GH70 Family.

Leuconostoc citreumNRRL B-742 has been known for years to produce a highly α-(1→3)-branched dextran for which the synthesis had never been elucidated. In this work a gene coding for a putative α-transglucosylase of the GH70 family was identified in the reported genome of this bacteria and functionally characterized. From sucrose alone, the corresponding recombinant protein, named BRS-B, mainly catalyzed sucrose hydrolysis and leucrose synthesis.