Carbohydrate recognition mechanism of HA70 from Clostridium botulinum deduced from X-ray structures in complexes with sialylated oligosaccharides

► Clostridium botulinum neurotoxin forms a progenitor complex with hemagglutinins. ► X-ray structures of the hemagglutinin/oligosaccharides complexes were determined. ► α2-3-Sialylated oligosaccharide bound to hemagglutinin tightly. ► α2-6-Sialylated oligosaccharide bound to hemagglutinin with a low occupancy. ► A binding assay also showed a higher affinity for α2-3-sialylated oligosaccharide.