Effect of xylitol on salivary ß-glucosidase in humans.

Dental biofilm - in which a diverse set of microorganisms are embedded in a complex polysaccharide matrix that adheres to oral components - is one of the most complex microbial communities in the human body. As biofilm formation is related to oral infections, such as caries and periodontal diseases, strategies for biofilm control are crucial for maintaining oral health. Xylitol, a synthetic sugar used as a sucrose substitute, has been shown to reduce biofilm formation. However, its precise mechanism of action on biofilm reduction has so far not been elucidated. Previous studies demonstrate that bacterial ß-glucosidase action is crucial for biofilm formation. Here, we investigated the correlation between salivary ß-glucosidase activity and dental plaque occurrence. We found a positive correlation between enzymatic activity and the presence of dental biofilm. We observed that xylitol inhibits ß-glucosidase in human saliva. Kinetic studies also confirmed that xylitol acts as a mixed type inhibitor of salivary ß-glucosidase. Based on our data, we suggest that xylitol impairs oral biofilm formation by the inhibition of bacterial ß-glucosidase, which is essential for biofilm formation in the oral cavity.

Beta glucosidase from Bacillus polymyxa is activated by glucose-6-phosphate.

Optimization of cellulose enzymatic hydrolysis is crucial for cost effective bioethanol production from lignocellulosic biomass. Enzymes involved in cellulose hydrolysis are often inhibited by their end-products, cellobiose and glucose. Efforts have been made to produce more efficient enzyme variants that are highly tolerant to product accumulation; however, further improvements are still necessary. Based on an alternative approach we initially investigated whether recently formed glucose could be phosphorylated into glucose-6-phosphate to circumvent glucose accumulation and avoid inhibition of beta-glucosidase from Bacillus polymyxa (BGLA). The kinetic properties and structural analysis of BGLA in the presence of glucose-6-phosphate (G6P) were investigated. Kinetic studies demonstrated that enzyme was not inhibited by G6P. In contrast, the presence of G6P activated the enzyme, prevented beta glucosidase feedback inhibition by glucose accumulation and improved protein stability. G6P binding was investigated by fluorescence quenching experiments and the respective association constant indicated high affinity binding of G6P to BGLA. Data reported here are of great impact for future design strategies for second-generation bioethanol production.