The binding specificities of the adhesive protein associated with the fimbriae of Bacteroides loeschei (now Prevotella loeschei) that mediates coaggregation with Streptococcus oralis and agglutination of RBCs has been further characterized. Studies with 125I-labeled adhesin established that its interaction with the streptococcal cell receptor is indeed a lectin-carbohydrate interaction readily reversed by amino sugars. Interaction with the carbohydrate receptor on S. oralis, prevents the streptococcus from coaggregating with its other partner cells, i.e., Actinomyces naeslundii, Veillonella atypica and Streptococcus sanguis. However, adhesion to PBCs or RBC ghosts appears to be a protein-protein interaction. The adhesin also binds to a number of eucaryotic structural proteins including laminin and fibronectin. Limited proteolysis studies indicate that the streptococcal-specific adhesin is antigenically related to the second adhesin which mediates coaggregation between P. loeschei and Actinomyces israelii. Currently the gene encoding the streptococcal-specific adhesin is being sequenced to determine its structure; this was facilitated by obtaining an internal peptide sequence of the adhesive protein. A mRNA transcript of the gene was identified; from its size, 2.9 kb, it appears that, at least, one other protein is being synthesized concomitantly with the adhesin.
