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Journal of Bacteriology, May 2009, p. 3011-3023, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.01601-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of the Streptococcus pneumoniae BgaC Protein as a Novel Surface β-Galactosidase with Specific Hydrolysis Activity for the Galβ1-3GlcNAc Moiety of Oligosaccharides{triangledown}

Jae Kap Jeong,1,{dagger} Ohsuk Kwon,1,{dagger} Yun Mi Lee,1 Doo-Byoung Oh,1 Jung Mi Lee,1 Seonghun Kim,1 Eun-Hye Kim,2 Tu Nhat Le,2 Dong-Kwon Rhee,2* and Hyun Ah Kang3*

Integrative Omics Research Center, KRIBB, Daejeon 305-333, South Korea,1 College of Pharmacy, Sungkyunkwan University, Suwon 440-746, South Korea,2 Department of Life Science, Chung-Ang University, Seoul 156-756, South Korea3

Received 11 November 2008/ Accepted 19 February 2009

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.

* Corresponding author. Mailing address for Dong-Kwon Rhee: College of Pharmacy, Sungkyunkwan University, Suwon 440-746, South Korea. Phone: 82-31-290-7707. Fax: 82-31-290-7727. E-mail: dkrhee{at}skku.edu. Mailing address for Hyun Ah Kang: Department of Life Science, Chung-Ang University, 221 Heukseok-dong, Dongjak-gu, Seoul 156-756, South Korea. Phone: 82-2-820-5863. Fax: 82-2-825- 5206. E-mail: hyunkang{at}cau.ac.kr

{triangledown} Published ahead of print on 6 March 2009.

{dagger} J. K. Jeong and O. Kwon contributed equally to this study.

Journal of Bacteriology, May 2009, p. 3011-3023, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.01601-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



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