Lactobacillus plantarum WCFS1 ß-Fructosidase: Evidence for an Open Funnel-Like Channel Through the Catalytic Domain with Importance for the Substrate Selectivity.

ß-Fructosidase, a glycoside hydrolase of a biotechnologically important strain, was studied for its biochemical, physicochemical, and three-dimensional structure characteristics. This enzyme was heterologously expressed in Escherichia coli as a C-terminal His-tagged protein (SacB). ß-Fructosidase catalyzes the cleavage of glycoside bonds toward certain carbohydrates with ß-fructofuranosyl linkages; however, SacB exhibited selectivity toward sucrose and an optimum activity at pH 6.0-6.5 and 37 °C. In such optimum enzymatic activity conditions, the SacB was commonly observed as a monodisperse protein by dynamic light scattering (DLS). As ß-fructosidase belongs to glycoside hydrolase family 32 (GH32), a ß-sandwich and a five-bladed ß-propeller domain are typical predicted folds in its structure. Docking and molecular dynamic simulations revealed for the first time a funnel-like channel perfectly exposed in the ß-propeller domain of the Lactobacillus plantarum ß-fructosidase (this allows the interaction between its entire catalytic triad and substrates that are larger than sucrose). In contrast, SacB showed a closed central tunnel collaterally induced by its His-tag.