Cell surface proteins of oral streptococci.

Whole cells of representative strains of oral streptococci (Streptococcus sanguis, S. mitis, and S. salivarius) were radiolabeled by the lactoperoxidase method of radioiodination. The labeled polypeptides obtained by extraction of whole cells with boiling sodium dodecyl sulfate were analyzed by polyacrylamide gel electrophoresis and autoradiography. Of the total radioactivity, ca. 70% was released by treating whole cells with trypsin, suggesting that the labeling was confined to proteins located on the cell surface. Most S. sanguis strains studied gave a characteristic banding pattern consisting of a high-molecular-weight (120,000 [120K] to 63K) group of six proteins. Three low-molecular-weight (12K, 16K, and 18K) proteins were also detected in many strains.