Binding Affinity of Actinobacillus actinomycetemcomitans for extracellular matrix proteins

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Actinobacillus actinomycetemcomitans is an aetiologic agent in the development of periodontal and some systemic diseases in humans. In this study, the binding affinity of A. actinomycetemcomitans to 4 kinds of extracellular matrix protein (collagen type I, collagen type IV, fibronectin, and laminin) was investigated. A. actinomycetemcomitansY4 and IDH781 bound to immobilized fibronectin and collagen type IV more than collagen type I and laminin. The binding of the cells to immobilized fibronectin and type IV collagen was inhibited by both of soluble fibronectin and collagen type N. The soluble fibronectin, but not the soluble collagen type IV bound to the 40-kDa proteins that were extracted from Y4 and IDH781 cells. These results suggest that Actinobacillus actinomycetemcomitansY4 and IDH781 have high binding affinity for fibronectin and this binding may be regulated with the 40-kDa bacterial cell proteins. Y4 and IDH781 also showed high affinity for collagen type IV and the non-protein component of bacterial cells may be involved in binding to collagen type IV.The cell surface protein antigen (PAg) and glucosyltransferases (GTFs) produced by Streptococcus sobrinus are major colonization factors of the organism, and the inhibition of these two factors should provide protection against dental caries. In this study, we constructed a fusion protein (PAgA-GB) composed of the alanine-rich region of PAg and the glucan-binding domain of GTF, and the antibodies against the fusion protein were prepared in rabbits. The antibody against PAgA-GB significantly inhibited the sucrose-dependent adhesion, but not sucrose-independent adhesion. These results show that the antibody against GTF-I may be useful for effective inhibition of the sucrose-dependent adhesion of S. sobrinus. However, PAg of S sobrinus may not function primarily as a receptor for acquired pellicles, and other cell surface proteins may be involved in the sucrose-independent adhesion of S sobrinus.