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|Title:||Molecular Characterization of N-glycan Degradation and Transport in Streptococcus pneumoniae and Its Contribution to Virulence.|
Hobbs, J. K.
Woodiga, S. A.
Suits, M. D.
King, S. J.
Boraston, A. B.
|Publisher:||Public Library of Science|
|Citation:||PLoS Pathogens, 2017, 13(1): e1006090|
|Abstract:||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.|
|Rights:||© 2017 Robb et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.|
|Description:||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).|
|Appears in Collections:||Published Articles, Dept. of Infection, Immunity and Inflammation|
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