Interaction of Salivary alpha-Amylase and Amylase-Binding-Protein A (AbpA) of <it>Streptococcus gordonii</it> with Glucosyltransferase of <it>S. gordonii</it> and <it>Streptococcus mutans</it>

<p>Abstract</p> <p>Background</p> <p>Glucosyltransferases (Gtfs), enzymes that produce extracellular glucans from dietary sucrose, contribute to dental plaque formation by <it>Streptococcus gordonii </it>and <it>Streptococcus mutans</it>. The alpha-amylase-binding protein A (AbpA) of <it>S. gordonii</it>, an early colonizing bacterium in dental plaque, interacts with salivary amylase and may influence dental plaque formation by this organism. We examined the interaction of amylase and recombinant AbpA (rAbpA), together with Gtfs of <it>S. gordonii </it>and <it>S. mutans</it>.</p> <p>Results</p> <p>The addition of salivary alpha-amylase to culture supernatants of <it>S. gordonii </it>precipitated a protein complex containing amylase, AbpA, amylase-binding protein B (AbpB), and the glucosyltransferase produced by <it>S. gordonii </it>(Gtf-G). rAbpA was expressed from an inducible plasmid, purified from <it>Escherichia coli </it>and characterized. Purified rAbpA, along with purified amylase, interacted with and precipitated Gtfs from culture supernatants of both <it>S. gordonii </it>and <it>S. mutans</it>. The presence of amylase and/or rAbpA increased both the sucrase and transferase component activities of <it>S. mutans </it>Gtf-B. Enzyme-linked immunosorbent assay (ELISA) using anti-Gtf-B antibody verified the interaction of rAbpA and amylase with Gtf-B. A <it>S. gordonii abp</it>A-deficient mutant showed greater biofilm growth under static conditions than wild-type in the presence of sucrose. Interestingly, biofilm formation by every strain was inhibited in the presence of saliva.</p> <p>Conclusion</p> <p>The results suggest that an extracellular protein network of AbpA-amylase-Gtf may influence the ecology of oral biofilms, likely during initial phases of colonization.</p>