Structure/function implications of glycan binding.

(A) The effect of selected mutations on the hemolytic activity of VCC is displayed as the ratio of the concentration of half-activity (HD₅₀) for each mutant relative to wild-type toxin. (B) Crystal structure of the VCC β-prism domain with the composite GlcNAcMan₃ model superimposed. The effects of mutations described in (A) are color coded and displayed on the protein surface. The inset box shows a closeup of the D617, L707, W706 core in a similar orientation. (C) Model for complex N-glycan binding based on the RbmC2 mannotriose structure, GlcNAc-Man structure, and mutagenesis data. The pentasaccharide core is shown boxed on a schematic representation of a complex N-glycan. Yellow arrows indicate the point of attachment of the subsequent two galactosyl moieties in a typical glycan and blue arrow denotes the attachment point of the double N-acetylglucosamine stem that attaches the glycan to asparagine residues on cell-surface proteins. The RbmC2 PVQGT loop insertion is colored orange and the surface of W706 colored yellow.