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The cholesterol-dependent cytolysins pneumolysin and streptolysin O require binding to red blood cell glycans for

Lucy K Shewell1, Richard M Harvey2, Melanie A Higgins2

  • 1Institute for Glycomics, Griffith University, Gold Coast, QLD 4222, Australia;

Proceedings of the National Academy of Sciences of the United States of America
|November 26, 2014
PubMed

Insights

Cholesterol-dependent cytolysins like pneumolysin bind to sialyl LewisX glycolipids, not just cholesterol. This interaction is crucial for toxin activity and reveals new cellular receptors for pore-forming toxins.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • Cholesterol-dependent cytolysins (CDCs) are key virulence factors.
  • Pore-forming toxins like pneumolysin (Ply) require membrane cholesterol for activity.
  • The specific cellular receptors for CDCs beyond cholesterol remain largely undefined.

Purpose of the Study:

  • To investigate the cellular receptors for pneumolysin (Ply).
  • To determine if Ply interacts with specific glycans.
  • To elucidate the role of glycan binding in CDC activity and target cell tropism.

Main Methods:

  • Glycan microarray analysis to identify Ply binding targets.
  • Surface plasmon resonance to quantify Ply-glycan affinity.
  • Flow cytometry and Western blotting to assess Ply binding to red blood cells (RBCs).
  • Site-directed mutagenesis to investigate the role of specific Ply domains in binding and activity.

Main Results:

  • Ply exhibits lectin activity, binding to glycans including Lewis histo-blood group antigens.
  • Ply shows highest affinity for sialyl LewisX (sLeX) glycolipids.
  • sLeX inhibits Ply hemolytic activity and blocks its binding to RBC membranes.
  • Mutagenesis of predicted carbohydrate-binding sites in Ply's domain 4 reduces sLeX affinity and hemolytic activity.
  • Streptolysin O also demonstrates glycan-binding properties.

Conclusions:

  • Sialyl LewisX is an essential cellular receptor for pneumolysin, mediating its binding before membrane insertion.
  • This finding challenges the traditional view of cholesterol as the sole CDC receptor.
  • Glycan-binding properties of CDCs contribute to their target cell specificity, suggesting a broader role for glycans in toxin-host interactions.

Keywords:
Streptococcus pneumoniaecholesterol-dependent cytolysinglycan bindingpneumolysinstreptolysin O

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