Abstract
BackgroundCollagen-like surface proteins Scl1 and Scl2 on Streptococcus pyogenes contain contiguous Gly-X-X triplet amino acid motifs, the characteristic structure of human collagen. Although the potential role of Scl1 in adhesion has been studied, the conclusions may be affected by the use of different S. pyogenes strains and their carriages of various adhesins. To explore the bona fide nature of Scl1 in adherence to human epithelial cells without the potential interference of other streptococcal surface factors, we constructed a scl1 isogenic mutant from the Scl2-defective S. pyogenes strain and a Scl1-expressed Escherichia coli.ResultsLoss of Scl1 in a Scl2-defective S. pyogenes strain dramatically decreased the adhesion of bacteria to HEp-2 human epithelial cells. Expression of Scl1 on the surface of the heterologous bacteria E. coli significantly increased adhesion to HEp-2. The increase in adhesion was nullified when Scl1-expressed E. coli was pre-incubated with proteases or antibodies against recombinant Scl1 (rScl1) protein. Treatment of HEp-2 cells with rScl protein or pronase drastically reduced the binding capability of Scl1-expressed E. coli. These findings suggest that the adhesion is mediated through Scl1 on bacterial surface and protein receptor(s) on epithelial cells. Further blocking of potential integrins revealed significant contributions of α2 and β1 integrins in Scl1-mediated binding to epithelial cells.ConclusionsTogether, these results underscore the importance of Scl1 in the virulence of S. pyogenes and implicate Scl1 as an adhesin during pathogenesis of streptococcal infection.
Highlights
Collagen-like surface proteins Scl1 and Scl2 on Streptococcus pyogenes contain contiguous Gly-X-X triplet amino acid motifs, the characteristic structure of human collagen
Identification and analysis of scl1 and scl2 genes in S. pyogenes M29588 strain To identify genes encoding streptococcal collagen-like surface protein 1 and 2 in S. pyogenes M29588 strain, full lengths of scl1 and scl2 genes were amplified by PCR and sequenced
The scl1 ORF of S. pyogenes M29588 is 1,287 bp, which encodes a protein with 428 amino acid residues (Figure 1A)
Summary
Collagen-like surface proteins Scl and Scl on Streptococcus pyogenes contain contiguous Gly-X-X triplet amino acid motifs, the characteristic structure of human collagen. The potential role of Scl in adhesion has been studied, the conclusions may be affected by the use of different S. pyogenes strains and their carriages of various adhesins. Many cell surface proteins of gram-positive bacteria share similar structural characteristics that include a variable amino terminus, a central region with repeated sequences, and a cell-associated region with a LPXTGX cell wall anchored motif [4]. A new S. pyogenes cell surface protein family, streptococcal collagen-like (Scl) protein, has been identified recently [5,6,7,8,9,10]. The presence of other Scl family proteins, as well as other streptococcal surface proteins, which may mask the potential role of Scl in adhesion, was not taken into consideration in these studies
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