Characterization of the Streptococcus pneumoniae BgaC protein as a novel surface β-galactosidase with specific hydrolysis activity for the Galβ1-3GlcNAc moiety of oligosaccharides

Jae Kap Jeong, Ohsuk Kwon, Yun Mi Lee, Doo Byoung Oh, Jung Mi Lee, Seonghun Kim, Eun Hye Kim, Tu Nhat Le, Dong Kwon Rhee, Hyun Ah Kang

Research output: Contribution to journalArticle

34 Scopus citations

Abstract

Streptococcus pneumoniae is a causative agent of high morbidity and mortality. Although sugar moieties have been recognized as ligands for initial contact with the host, only a few exoglycosidases have been reported to occur in S. pneumoniae. In this study, a putative β-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 Galβ1-3-GlcNAc moiety of oligosaccharides. 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 sequence or membrane anchorage motif. The surface localization of BgaC was further supported by immunofluorescence microscopy analysis using an antibody raised against BgaC and by a reassociation assay with fluorescein isothiocyanate-labeled BgaC. Although the bgaC deletion mutation did not significantly attenuate the virulence of S. pneumoniae in vivo, the bgaC mutant strain showed relatively low numbers of viable cells compared to the wild type after 24 h of infection in vivo, whereas the mutant showed higher colonization levels at 6 and 24 h postinfection 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.

Original languageEnglish (US)
Pages (from-to)3011-3023
Number of pages13
JournalJournal of bacteriology
Volume191
Issue number9
DOIs
StatePublished - May 2009

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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