Characterization of the Streptococcus pneumoniae BgaC protein as a novel surface beta-galactosidase with specific hydrolysis activity for the Galbeta1-3GlcNAc moiety of oligosaccharides.
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 beta-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 Galbeta1-3-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 beta-galactosidase with high substrate specificity that is significantly associated with the infection activity of pneumococci.
Jeong
Jae Kap
JK
College of Pharmacy, Sungkyunkwan University, Suwon 440-746, South Korea.
Kwon
Ohsuk
O
Lee
Yun Mi
YM
Oh
Doo-Byoung
DB
Lee
Jung Mi
JM
Kim
Seonghun
S
Kim
Eun-Hye
EH
Le
Tu Nhat
TN
Rhee
Dong-Kwon
DK
Kang
Hyun Ah
HA
D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001769:Blood / Q000382:microbiology; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000235:genetics; D017353:Gene Deletion; D015870:Gene Expression; D006868:Hydrolysis; D008168:Lung / Q000382:microbiology; D051379:Mice; D050296:Microbial Viability; D009305:Nasopharynx / Q000382:microbiology; D009844:Oligosaccharides / Q000378:metabolism*; D011008:Pneumococcal Infections / Q000382:microbiology; D021382:Protein Sorting Signals; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification; D013296:Streptococcus pneumoniae / Q000201:enzymology* / Q000472:pathogenicity; D013379:Substrate Specificity; D014774:Virulence; D001616:beta-Galactosidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D009844:Oligosaccharides; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D001616:beta-Galactosidase