Proteolytic degradation of human salivary MUC5B by dental biofilms

The degradation of complex substrates, like salivary mucins, requires an arsenal of glycosidases and proteases to sequentially degrade the oligosaccharides and polypeptide backbone. The mucin MUC5B is a complex oligomeric glycoprotein, heterogeneous in molecular mass (14-40×10⁶ Da), with a diverse repertoire of oligosaccharides, differing in composition and charge. The aim of this study was to investigate whether proteolytic degradation of the mucin polypeptide backbone could be identified and if cooperation of dental biofilm bacteria was required. Cooperative bacteria-mediated proteolysis of MUC5B was determined by comparing individual species and mixed consortia of strains isolated from supragingival plaque, and freshly harvested supragingival plaque. Proteolytic activity was analysed using fluorescent labelled substrate and by visualizing mucin degradation by SDS-PAGE. Dental plaque degraded the polypeptide backbone of the salivary MUC5B mucin. The mucin was also degraded by a specific consortium of isolated species from supragingival plaque, although individual species and other consortia did not. Certain bacteria in supragingival dental plaque therefore cooperate as a consortium to proteolyse human salivary MUC5B and hydrolyse glycosides.