PMID:21602213

Citation	Limoli, DH, Sladek, JA, Fuller, LA, Singh, AK and King, SJ (2011) BgaA acts as an adhesin to mediate attachment of some pneumococcal strains to human epithelial cells. Microbiology (Reading, Engl.) 157:2369-81
Abstract	Streptococcus pneumoniae colonization of the respiratory tract is an essential precursor for pneumococcal disease. To colonize efficiently, bacteria must adhere to the epithelial-cell surface. S. pneumoniae possesses surface-associated exoglycosidases that are capable of sequentially deglycosylating human glycans. Two exoglycosidases, neuraminidase (NanA) and β-galactosidase (BgaA), have previously been shown to contribute to S. pneumoniae adherence to human epithelial cells, as deletion of either of these genes results in reduced adherence. It has been suggested that these enzymes may modulate adherence by cleaving sugars to reveal a receptor on host cells. Pretreatment of epithelial cells with exogenous neuraminidase restores the adherence of a nanA mutant, whereas pretreatment with β-galactosidase does not restore the adherence of a bgaA mutant. These data suggest that BgaA may not function to reveal a receptor, and implicate an alternative role for BgaA in adherence. Here we demonstrate that β-galactosidase activity is not required for BgaA-mediated adherence. Addition of recombinant BgaA (rBgaA) to adherence assays and pretreatment of epithelial cells with rBgaA both significantly reduced the level of adherence of the parental strain, but not the BgaA mutant. One possible explanation of these data is that BgaA is acting as an adhesin and that rBgaA is binding to the receptor, preventing bacterial binding. A bead-binding assay demonstrated that BgaA can bind directly to human epithelial cells, supporting the hypothesis that BgaA is an adhesin. Preliminary characterization of the epithelial-cell receptor suggests that it is a glycan in the context of a glycosphingolipid. To further establish the relevance of this adherence mechanism, we demonstrated that BgaA-mediated adherence contributed to adherence of a recent clinical isolate to primary human epithelial cells. Together, these data suggest a novel role for BgaA as an adhesin and suggest that this mechanism could contribute to adherence of at least some pneumococcal strains in vivo.
Links	PubMed PMC3167885 Online version:10.1099/mic.0.045609-0
Keywords	Adhesins, Bacterial/genetics; Adhesins, Bacterial/metabolism; Bacterial Adhesion; Cells, Cultured; Epithelial Cells/microbiology; Humans; Polysaccharides/metabolism; Streptococcus pneumoniae/pathogenicity; beta-Galactosidase/genetics; beta-Galactosidase/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
STRP2:Q04LN6		GO:0009986: cell surface	ECO:0000315:		C		Fig.1 showing relative adherence of mutants with mutations in the bgaA gene protein product, indication that the protein is found on cell surface, due to its involvement in cell to cell binding.	complete CACAO 3657
STREE:Q9KGU0		GO:0016787: hydrolase activity	ECO:0000315:		F		Figure 2b indicates evidence of hydrolase activity, more specificly beta- galactosidase activity.	complete CACAO 3797
STREE:Q9KGU0		GO:0007155: cell adhesion	ECO:0000314:		P		Figure 6 - Assay demonstrated that "BgaA contributes to the adherence of encapsulated pneumococci to human epithelial cells"	complete CACAO 3837
STREE:Q9KGU0	involved_in	GO:0007155: cell adhesion	ECO:0000314: direct assay evidence used in manual assertion		P		Seeded From UniProt	complete
STREE:Q9KGU0	enables	GO:0016787: hydrolase activity	ECO:0000315: mutant phenotype evidence used in manual assertion		F		Seeded From UniProt	complete

References

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