Function and immunogenicity of cell-wall-anchored polypeptide CshA in oral streptococci.

Abstract

Streptococcus gordonii is found at most sites in the human oral cavity (2) and has a high affinity for binding to salivary pellicle and other oral microbial cells (7). CshA (259 kDa) and CshB (c. 245 kDa) are wall-anchored polypeptides in S. gordonii. Gene inactivation experiments have shown that these polypeptides are associated with conferring cell-surface hydrophobicity and the ability to bind to oral Actinomyces, and are essential for S. gordonii colonization of the murine oral cavity (4). Evidence suggests that CshA and CshB work in conjunction with at least two additional cell-surface proteins designated SspA and SspB (1) to mediate adhesion of S. gordonii cells to Actinomyces. CshA and CshB are immunologically cross-reactive and this is attributed to the sequence similarity of the amino acid residue repeat block region that makes-up approximately 60% of the total sequence of each polypeptide (4). Polypeptides cross-reactive with CshA antibodies are found amongst the “sanguis group” streptococci (5). To delineate the adhesion-mediating sequences within CshA, purified recombinant fragments comprising the N-terminal non-repetitive (NR) region and a segment of the C-terminal repetitive (R) region were tested for ability to bind various substrates, and antibodies raised to these fragments were utilized in binding-inhibition assays of S. gordonii cells.