Characterization of an adhesion antigen of Streptococcus sanguis G9B.

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RESUMO

An antigen possessing the attributes of an adhesion has been identified in Streptococcus sanguis G9B. Cell surface components were extracted from G9B and a spontaneously occurring nonadherent mutant of G9B, strain Adh-, with a 2 mM barbital buffer, pH 8.6. The extract of G9B but not of Adh- absorbed more than 80% of the adhesion-inhibitory activity of anti-G9B immunoglobulin G (IgG). Immunoblots revealed 80- and 52-kilodalton (kDa) antigens present in the G9B extract but not in the Adh- extract. Absorption of anti-G9B IgG with Adh- and G9B barbital extracts showed a correlation between the loss of the 80- and 52-kDa antibodies and the loss of adhesion-inhibitory activity. An antibody prepared against the 80-kDa antigen excised from sodium dodecyl sulfate-polyacrylamide gels recognized the 80- and 52-kDa antigens and another antigen of 62 kDa but did not inhibit adhesion. However, an antibody from an electroblot containing the native protein from which the 80-kDa and related antigens were derived (the 80-kDa antigen complex) inhibited adhesion to the same extent as anti-G9B IgG. Periodate oxidation of the G9B barbital extract modified the 80-kDa antigen complex and resulted in the loss of 40% of its absorbing activity. The barbital extract also contained an endogenous enzyme responsible for producing the 62- and 52-kDa antigens from the 80-kDa protein and which, under optimal conditions, degraded the antigen completely, resulting in the loss of antibody-absorbing activity. The 80-kDa antigen complex has a molecular mass of more than 200 kDa in native polyacrylamide gels and a pI of 4.1 to 4.8. These observations suggest that the adhesion antigen in S. sanguis G9B is a large glycoprotein from which an 80-kDa antigen complex is derived.

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