Identification and structural basis of binding to host lung glycogen by streptococcal virulence factors

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The ability of pathogenic bacteria to recognize host glycans is often essential to their virulence. Here we report structure-function studies of previously uncharacterized glycogen-binding modules in the surface-anchored pullulanases from Streptococcus pneumoniae (SpuA) and Streptococcus pyogenes (PulA). Multivalent binding to glycogen leads to a strong interaction with alveolar type II cells in mouse lung tissue. X-ray crystal structures of the binding modules reveal a novel fusion of tandem modules into single, bivalent functional domains. In addition to indicating a structural basis for multivalent attachment, the structure of the SpuA modules in complex with carbohydrate provides insight into the molecular basis for glycogen specificity. This report provides the first evidence that intracellular lung glycogen may be a novel target of pathogenic streptococci and thus provides a rationale for the identification of the streptococcal α-glucan–metabolizing machinery as virulence factors.

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Figure 1: Primary structure analysis of PulA and SpuA.
Figure 2: Carbohydrate macroarray with streptococcal family 41 CBMs.
Figure 3: Binding properties of SpnDX and SpyDX.
Figure 4: Structure of SpyDX.
Figure 5: SpnDX with ligand present in both binding grooves.
Figure 6: Mouse lung tissue probed with FITC-labeled SpyDX and SpnDX.
Figure 7: Localization of SpyDX and SpnDX to alveolar type II cells.

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We thank R. Chow for providing access to and assistance with the confocal imaging microscope. This work was supported by grants from the Canadian Institutes of Health Research and Natural Sciences and Engineering Council of Canada (A.B.B. and R.D.B.). A.L.v.B. is supported by doctoral fellowships from the Michael Smith Foundation for Health Research and the Natural Sciences and Engineering Research Council of Canada. A.B.B. is a Canada Research Chair in Molecular Interactions.

Author information

A.L.v.B., cloning, protein production and purification, binding studies, crystallization, structure solution and analysis and figure and manuscript preparation; M.H., cloning and protein production and purification; D.W., lung section preparation and probing; R.D.B., fluorescence and confocal microscopic imaging and figure preparation; A.B.B., principle investigator and figure and manuscript preparation.

Correspondence to Alisdair B Boraston.

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