IDENTIFICATION OF A NOVEL LECTIN IN STREPTOCOCCUS-PYOGENES AND ITS POSSIBLE ROLE IN BACTERIAL ADHERENCE TO PHARYNGEAL CELLS

During investigation of the interaction of human lactoferrin (HLf) wit h various bacteria, it was found that, in Streptococcus pyogenes, HLf binding occurred to agar- rather than broth-grown cells irrespective o f the nutrients used. Furthermore, binding of HLf to broth-grown, heat -killed bacteria was induced by overnight incubation on agar media or short-time exposure of the cells to water-soluble agar extract. The bi nding pattern was revealed in most of 92 S. pyogenes strains represent ing various M- or T-types with no apparent type variation. The compone nt thus bridging the attachment of HLf to the streptococcal cell surfa ce was recovered in extracts of agar-grown cells and isolated by affin ity chromatography on HLf-sepharose. By gel filtration in the presence of radiolabeled HLf, this component exhibited similar elution positio n as crude water-soluble agar extract. Chemical analysis identified th e active HLf-binding agar component to be a galactose-rich polysacchar ide (GRP). Further binding tests showed that the interaction between s treptococci and GRP was stable in the presence of high molar NaCl, KSC N, or urea and was unaffected by various serum or matrix proteins or b y streptococcal lipoteichoic acid; however, a moderate inhibition by h eparin or bovine mucin was observed. Studies on isogenic mutants of S. pyogenes did not support the involvement of M-protein or the hyaluron ate capsule in the binding of GRP. SDS-PAGE and Western blot analyses revealed a GRP-binding protein of approximately 70 kDa in the cell-wal l extracts of two strains of S. pyogenes, types M19 and M55. Finally, the adherence of (broth-grown) H-3-thymidine-labeled S. pyogenes, type M19, to the pharyngeal epithelial cell line DT-562 or to normal tonsi llar epithelial cells was inhibited by GRP in a dose-related manner. W e thus propose that the streptococcal GRP-binding component may repres ent a novel surface lectin acting as a mucosal adhesin for S. pyogenes , in accordance with previous data indicating that galactose-containin g sugar moieties may serve as ligands for the adherence of streptococc i to pharyngeal cells. Our results also indicate that GRP-like compone nts such as mucin or heparin might act to block epithelial adherence o f S. pyogenes at the mucosal level.