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Molecular Characterization of N-glycan Degradation and Transport in Streptococcus pneumoniae and Its Contribution to Virulence.

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posted on 2017-01-09, 14:56 authored by M. Robb, J. K. Hobbs, S. A. Woodiga, S. Shapiro-Ward, M. D. Suits, N. McGregor, H. Brumer, H. Yesilkaya, S. J. King, A. B. Boraston
The carbohydrate-rich coating of human tissues and cells provide a first point of contact for colonizing and invading bacteria. Commensurate with N-glycosylation being an abundant form of protein glycosylation that has critical functional roles in the host, some host-adapted bacteria possess the machinery to process N-linked glycans. The human pathogen Streptococcus pneumoniae depolymerizes complex N-glycans with enzymes that sequentially trim a complex N-glycan down to the Man3GlcNAc2 core prior to the release of the glycan from the protein by endo-β-N-acetylglucosaminidase (EndoD), which cleaves between the two GlcNAc residues. Here we examine the capacity of S. pneumoniae to process high-mannose N-glycans and transport the products. Through biochemical and structural analyses we demonstrate that S. pneumoniae also possesses an α-(1,2)-mannosidase (SpGH92). This enzyme has the ability to trim the terminal α-(1,2)-linked mannose residues of high-mannose N-glycans to generate Man5GlcNAc2. Through this activity SpGH92 is able to produce a substrate for EndoD, which is not active on high-mannose glycans with α-(1,2)-linked mannose residues. Binding studies and X-ray crystallography show that NgtS, the solute binding protein of an ABC transporter (ABCNG), is able to bind Man5GlcNAc, a product of EndoD activity, with high affinity. Finally, we evaluated the contribution of EndoD and ABCNG to growth of S. pneumoniae on a model N-glycosylated glycoprotein, and the contribution of these enzymes and SpGH92 to virulence in a mouse model. We found that both EndoD and ABCNG contribute to growth of S. pneumoniae, but that only SpGH92 and EndoD contribute to virulence. Therefore, N-glycan processing, but not transport of the released glycan, is required for full virulence in S. pneumoniae. To conclude, we synthesize our findings into a model of N-glycan processing by S. pneumoniae in which both complex and high-mannose N-glycans are targeted, and in which the two arms of this degradation pathway converge at ABCNG.


This research was supported by a Canadian Institute of Health Research (http://www. operating grant (MOP 130305) awarded to ABB. ABB also acknowledges the support of a Canada Research Chair in Molecular Interactions (, an E.W.R. Steacie Memorial Fellowship from the Natural Sciences and Engineering Research Council of Canada ( and a Michael Smith Foundation for Health Research Scholar Award ( Work in the Brumer lab was supported by the Natural Sciences and Engineering Research Council of Canada (via an Alexander Graham Bell Canada Graduate Doctoral Scholarship to NM and a Discovery Grant to HB), the Canada Foundation for Innovation ( and the British Columbia Knowledge Development Fund ( technologyandinnovation/Funding/BCKDF/). The Stanford Synchrotron Radiation Lightsource (SSRL) is a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University. The SSRL Structural Molecular Biology Program is supported by the Department of Energy Office of Biological and Environmental Research (http://, the National Institutes of Health (, National Center for Research Resources, Biomedical Technology Program (P41RR001209) and the National Institute of General Medical Sciences (https://www. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.



PLoS Pathogens, 2017, 13(1): e1006090

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/Organisation/COLLEGE OF MEDICINE, BIOLOGICAL SCIENCES AND PSYCHOLOGY/School of Medicine/Department of Infection, Immunity and Inflammation


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Coordinates and structure factors have been deposited with the following accession codes into the Protein Data Bank: SpGH92 in complex with mannose (5SWI); native NgtS (5SUO); NgtS in complex with Man1GlcNAc (5SWA); NgtS in complex with Man5GlcNAc (5SWB).



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