Molecularly Defined Glycocalyx Models Reveal AB₅ Toxins Recognize Their Target Glycans Superselectively

Area of Science:

• Biochemistry
• Cell Biology
• Materials Science

Background:

• AB5 toxins, including cholera toxin (CT) and Shiga toxin (STx), utilize cell surface carbohydrates for entry.
• While glycolipid ligands for CT and STx are known, the role of fucosylated structures like Lewis x (Le x) in CT binding is a recent discovery.
• The interaction of these toxins with non-glycolipid glycocalyx components remains poorly understood.

Purpose of the Study:

• To investigate the role of the glycocalyx in AB5 toxin binding and host cell selection.
• To develop and utilize synthetic glycocalyx models for studying toxin-glycan interactions.
• To analyze the kinetics and affinity of CT and STx binding to defined glycan structures.

Main Methods:

• Grafting mucin-like glycopolymers with specific oligosaccharides (Le x, Gb3, lactose) onto solid-supported lipid bilayers (SLBs) to create defined glycocalyx models.
• Utilizing quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry to characterize the models and quantify toxin binding.
• Analyzing the binding kinetics and affinity of CT and STx B subunit pentamers to the model glycocalyces.

Main Results:

• Model glycocalyces with defined thickness, mesh size, and glycan concentration were successfully created.
• CT and STx B subunit pentamers exhibited significantly enhanced binding affinity in the model glycocalyx environment due to multivalent interactions.
• Toxin binding demonstrated a superlinear increase with target glycan concentration, suggesting a "superselective" binding mechanism.

Conclusions:

• Multivalent binding within a model glycocalyx significantly enhances AB5 toxin affinity.
• "Superselective" binding, dependent on target glycan concentration, may be crucial for host cell selection by bacterial toxins.
• The developed glycocalyx models offer a novel platform for studying complex protein-glycan interactions and designing targeted toxin-binding systems.