STRUCTURAL AND ANTIGENIC CHARACTERISTICS OF STREPTOCOCCUS-SOBRINUS GLUCAN BINDING-PROTEINS

Three purified glucan binding proteins (GBP-2, GBP-3, and GBP-5) from Streptococcus sobrinus 6715 were compared structurally by mass spectro scopy of tryptic fragments and antigenically by Western blot analysis with rat antisera to each GBP or to peptides containing putative gluca n binding epitopes of mutans streptococcal glucosyltransferases. Struc tural and antigenic analyses indicated that GBP-3 and GBP-5 are very s imilar but that both are essentially unrelated to GBP-2. None of these S. sobrinus GBPs appeared to have a strong antigenic relationship wit h GBPs from Streptococcus mutans. Thus, S. sobrinus GBP-2 and GBP-3 ap pear to be distinct proteins with potentially different functions. S. sobrinus GBP-5 may be a proteolytic fragment of GBP-3, or, alternative ly, the genes coding for these proteins may be closely related.