The rnc Gene Regulates the Microstructure of Exopolysaccharide in the Biofilm of Streptococcus mutans through the ß-Monosaccharides.

Streptococcus mutans is known as the crucial pathogen of human dental caries, owing to its contribution to the biofilm development via the capacity of synthesizing exopolysaccharide (EPS), which mainly compose of α-glycosidic bond and ß-glycosidic bond. ß-glycosidic bond is less flexible than α-glycosidic bond because of differences between their configurational properties. Previous studies have shown that the rnc gene is implicated in the EPS formation and the cariogenicity of S. mutans. However, the effects of rnc on the microstructure of EPS have been not well-understood yet. Here, we further investigated how the rnc gene worked to modulate microstructural properties of the extracellular polysaccharide of S. mutans using glycomics methods. The gas chromatography-mass spectrometer showed that the proportion of glucose was decreased in water-soluble EPS and galactose was absent in water-insoluble EPS from the S. mutans rnc-deficient strain (Smurnc), compared with the isogenic wild-type strain (UA159). The composition of functional groups and the displacement of hydrogen bond were analyzed by infrared radiation and 1H nuclear magnetic resonance, respectively. In addition, phenotypic modulation of the biofilm matrix was assessed by microscopy. We found that the EPS of UA159 and the rnc overexpression strain (Smurnc+) mainly consisted of ß-glycosidic bonds. Conversely, the EPS of Smurnc were made up of mostly α-glycosidic bonds, leading to the attenuation of biofilm biomass and bacterial adhesion. Furthermore, the existence of ß-glycosidic bond was verified by enzyme digestion. Collectively, the rnc gene modulates the conversion of ß-glycosidic bonds, which may play important roles in regulating the micromolecule structure of the EPS matrix, thus affecting the characteristics of S. mutans biofilm. These data illustrate that ß-glycosidic bonds mediated by rnc may be potential targets for the prevention and treatment of dental caries.

Immobilized Crosslinked Pectinase Preparation on Porous ZSM-5 Zeolites as Reusable Biocatalysts for Ultra-Efficient Hydrolysis of ß-Glycosidic Bonds.

In this study, we immobilized pectinase preparation on porous zeolite ZSM-5 as an enzyme carrier. We realized this immobilized enzyme catalyst, pectinase preparation@ZSM-5, via a simple combined strategy involving the van der Waals adsorption of pectinase preparation followed by crosslinking of the adsorbed pectinase preparation with glutaraldehyde over ZSM-5. Conformal pectinase preparation coverage of various ZSM-5 supports was achieved for the as-prepared pectinase preparation@ZSM-5. The porous pectinase preparation@ZSM-5 catalyst exhibited ultra-efficient biocatalytic activity for hydrolyzing the ß-glycosidic bonds in the model substrate 4-nitrophenyl ß-D-glucopyranoside, with a broad operating temperature range, high thermal stability, and excellent reusability. The relative activity of pectinase preparation@ZSM-5 at a high temperature (70 °C) was nine times higher than that of free pectinase preparation. Using thermal inactivation kinetic analysis based on the Arrhenius law, pectinase preparation@ZSM-5 showed higher activation energy for denaturation (315 kJ mol-1) and a longer half-life (62 min-1) than free pectinase preparation. Moreover, a Michaelis-Menten enzyme kinetic analysis indicated a higher maximal reaction velocity for pectinase preparation@ZSM-5 (0.22 µmol mg-1 min-1). This enhanced reactivity was attributed to the microstructure of the immobilized pectinase preparation@ZSM-5, which offered a heterogeneous reaction system that decreased the substrate-pectinase preparation binding affinity and modulated the kinetic characteristics of the enzyme. Additionally, pectinase preparation@ZSM-5 showed the best ethanol tolerance among all the reported pectinase preparation-immobilized catalysts, and an activity 247% higher than that of free pectinase preparation at a 10% (v/v) ethanol concentration was measured. Furthermore, pectinase preparation@ZSM-5 exhibited potential for practical engineering applications, promoting the hydrolysis of ß-glycosidic bonds in baicalin to convert it into baicalein. This was achieved with a 98% conversion rate, i.e., 320% higher than that of the free enzyme.