MOLECULAR DIVERSITY AMONG THE TRYPSIN RESISTANT SURFACE-PROTEINS OF GROUP-B STREPTOCOCCI

The alpha (alpha) component of the c protein and R proteins are trypsi n resistant, but antigenically distinct, proteins on the cell surface of some but not all strains of group B streptococci (GBS). These two c lasses of proteins, along with the group and type polysaccharide, can be used to characterize strains of GBS. Four species of R protein (R1 through R4) have been described. We studied trypsin extracts from nume rous strains of GBS by immunodiffusion in agarose and polyacrylamide g el electrophoresis/Western blot. Sera monospecific for alpha, R1 and R 4 were used to immunoprecipitate/blot the proteins. The molecular weig ht of the blotted proteins was determined. Although by immunodiffusion the proteins within a class were identical to each other; great heter ogeneity in size and blotting pattern was found within each class. Var iation was independent of the polysaccharide serotype. Multiple molecu lar weight species were seen for alpha, R1 and R4 proteins. For a give n strain, the various forms of alpha or R1 appeared to form a multiple size ladder; those of R4 were fewer and closer in size. The highest f orm of alpha ranged from 85 to 170 kDa, with 45 kDa being the highest form for some rare GBS strains. For R4 the predominant and highest for m varied from 84 to 197 kDa, whereas some strains with R1 had the high est form over 200 kDa. Our results indicated that despite similarities , there is great diversity among the alpha, R1 and R4 trypsin resistan t proteins of GBS.