Tandem genes encode cell‐surface polypeptides SspA and SspB which mediate adhesion of the oral bacterium Streptococcus gordonii to human and bacterial receptors

Abstract

The highly conserved antigen I/II family of polypeptides produced by oral streptococci are believed to be colonization determinants and may mediate adhesion of bacterial cells to salivary glycoproteins absorbed to cells and tissues in the human oral cavity. Streptococcus gordonii is shown to express, on the cell surface, two antigen I/II polypeptides designated SspA and SspB (formerly Ssp-5) that are the products of tandemly arranged chromosomal genes. The structure and arrangement of these genes is similar in two independently isolated strains, DL1 and M5, of S. gordonii. The mature polypeptide sequences of M5 SspA (1539 amino acid (aa) residues) and SspB (1462 aa residues) are almost wholly conserved (98% identical) in the C-terminal regions (from residues 796 in SspA and 719 in SspB, to the respective C-termini), well-conserved (84%) at the N-terminal regions (residues 1-429), and divergent (only 27% identical residues) within the intervening central regions. Insertional inactivation of the sspA gene in S. gordonii DL1 resulted in reduced binding of cells to salivary agglutinin glycoprotein (SAG), human erythrocytes, and to the oral bacterium Actinomyces naeslundii. Further reductions in streptococcal cell adhesion to SAG and to two strains of A. naeslundii were observed when both sspA and sspB genes were inactivated. The results suggest that both SspA and SspB polypeptides are involved in adhesion of S. gordonii cells to human and bacterial receptors.

Structure, function and immunogenicity of streptococcal antigen I/II polypeptides

“…Specifically, sialic acid residues of SAG were essential for its interaction with S. gordonii SspB polypeptide but were not required for binding S. mutans antigen I/II polypeptide (Demuth et al, 1990b). In addition, S. gordonii has recently been shown to possess tandem genes encoding two antigen I/II polypeptides, SspA and SspB (Demuth et al, 1996). Isogenic sspA sspB double mutants were unaffected in binding saliva-coated hydroxylapatite and only 50% reduced in binding to SAG.…”

“…Antigen I/II polypeptides SspA and SspB are implicated also in the binding of oral Actinomyces by S. gordonii. Insertional inactivation of the sspA and sspB genes generated mutant cells that were deficient in binding to A. naeslundii (Demuth et al, 1996). The regions within SspA and SspB that mediate this binding interaction have not yet been localized.…”

“…Recent evidence suggests that antigen I/II polypeptides are involved in the interactions of S. gordonii with P. gingivalis (Lamont et al, 1994), Candida albicans and Actinomyces naeslundii (Jenkinson et al, 1993;Demuth et al, 1996). S. gordonii surface polypeptides of molecular masses 62 kDa and 45 kDa that bound to intact P. gingivalis cells in a dose-dependent manner were found to be antigenically related to antigen I/II polypeptides (Lamont et al, 1994).…”

“…Within this divergent region (designated D in Fig. 1), the SspB protein, one of two antigen I/II polypeptides expressed by S. gordonii (Demuth et al, 1996), exhibits only 22% identity with the antigen I/II sequences of the mutans streptococci. Interestingly, the other I/II polypeptide (SspA) of S. gordonii more closely resembles the S. mutans protein sequences and may represent a naturally occurring chimera of S. gordonii and S. mutans I/II proteins.…”

Characterization of the complex bacterial communities colonizing biliary stents reveals a host-dependent diversity

“…The spatial closeness of points on the plot indicates their relative closeness in terms of their bacterial communities. (Nyvad and Kilian, 1990;Diaz et al, 2006), a process mediated by adhesins (Demuth et al, 1996;Jado et al, 2001). Adhesins to fibronectin and vitronectin known to coat biliary stent surfaces introduced into the human host (Yu et al, 1996) may also play a role in primary colonization of biliary stents.…”