Comparison of amylase-binding proteins in oral streptococci

Certain species of oral streptococci bind salivary amylase to their cell surface. The patterns of amylase-binding proteins produced by a range of streptococci have been compared by ligand blotting and several characteristics of the binding proteins investigated. Streptococcus gordonii was the most homogeneous species and almost all strains produced proteins migrating with molecular mass 82 kDa and 20 kDa. Other species were more heterogeneous, releasing proteins that resolved at 87 or 82 kDa and/or between 20 and 36 kDa. Binding of amylase to the 82/87-kDa proteins on ligand blots was prevented by amylase inhibitors, amylase substrates and periodate treatment but these had limited or no effect on amylase binding to 20-36 kDa proteins. Also, the 20 kDa protein of S. gordonii Challis was released into culture medium before the 82-kDa protein. These data suggest that there is significant variation in amylase-binding proteins among streptococci and that the high and low molecular mass proteins differ in the way they interact with salivary amylase.