title: Identification of a pneumococcal glycosidase that modifies O-linked glycans.
abstract: Colonization of the airway by Streptococcus pneumoniae is typically asymptomatic; however, progression of bacteria beyond the oronasopharynx can cause diseases including otitis media and pneumonia. The mechanisms by which S. pneumoniae establishes and maintains colonization remain poorly understood. Both N-linked and O-linked glycans are abundant in the airway. Our previous research demonstrated that S. pneumoniae can sequentially deglycosylate N-linked glycans and suggested that this modification of sugar structures may aid in colonization. There is published evidence that S. pneumoniae expresses a secreted O-glycosidase that cleaves galactose beta1-3 N-acetylgalactosamine (Galbeta1-3GalNAc) from core-1 O-linked glycans; however, the biological function of this enzyme has not previously been determined. We established that the activity is not secreted but is instead surface associated in a sortase-dependent manner. Genome analysis revealed an open reading frame predicted to encode a sortase-dependent surface protein with sequence similarity to the O-glycosidase of Bifidobacterium longum. Deletion of this pneumococcal open reading frame confirmed that this gene encodes an O-glycosidase. Experiments using a model glycoconjugate demonstrated that this O-glycosidase, together with the neuraminidase NanA, is required for S. pneumoniae to cleave sialylated core-1 O-linked glycans. The ability of the O-glycosidase mutant to cleave this glycan structure was restored by both genetic complementation and the addition of O-glycosidase. The mutant showed a reduction in adherence to human airway epithelial cells and a significantly decreased ability to colonize the upper respiratory tract, suggesting that cleavage of core-1 O-linked glycans enhances the ability of S. pneumoniae to colonize the human airway.
authors.affiliation: Center for Microbial Pathogenesis, The Research Institute at Nationwide Children's Hospital, Columbus, Ohio, USA.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Marion
authors.forename: Dominique H
authors.initials: DH
authors.lastname: Limoli
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Bobulsky
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Abraham
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Burnaugh
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: King
mesh_terms: D000818:Animals; D001422:Bacterial Adhesion; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000382:microbiology*; D006001:Glycoconjugates / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D009305:Nasopharynx / Q000382:microbiology; D016366:Open Reading Frames; D010614:Pharynx / Q000166:cytology / Q000382:microbiology*; D011008:Pneumococcal Infections / Q000382:microbiology; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D013296:Streptococcus pneumoniae / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology
chemical_list: D006001:Glycoconjugates; D011134:Polysaccharides; D006026:Glycoside Hydrolases