earticle

영어

Streptococcus pneumoniae is a causative agent for high morbidity and mortality. Although sugar moieties have been recognized as a ligand for initial contact with the host, only a few exoglycosidaseshave been reported in S. pneumoniae. In this study, a putative -galactosidase, encoded by the bgaC gene of S. pneumoniae, was characterized for its enzymatic activity and virulence. The recombinant BgaC protein, expressed and purified from Escherichia coli, was found to have a highly regiospecific and sugar specific hydrolysis activity for the Gal1-3-GlcNAc moiety of oligosaccharide. Interestingly, the BgaC hydrolysis activity was localized at the cell surface of S. pneumoniae, indicating that BgaC is expressed as a surface protein although it does not have a typical signal sequenceor membrane anchorage motif. The surface localization of BgaC was further supported by immunofluorescence microscopy analysis using an antibody raised against BgaC. Although the bgaC deletion mutation did not significantly attenuate the virulence of S. pneumoniae in vivo, the bgaC mutant strain showed relatively lower viable cell numbers compared to the wild type after 24 h infection in vivo, whereas it showed higher adherence and invasion at 6 and 12 h post- infection in vivo. Our data strongly indicate for the first time that S. pneumoniae bgaC encodes a surface β-galactosidase with high substrate specificity that is significantly associated with the infection activity of pneumococci.