Binding of Clostridium botulinum C2 Toxin to Asparagine-linked Complex and Hybrid Carbohydrates*

Abstract

Clostridium botulinum C2 toxin is a binary toxin composed of an enzymatic subunit (C2I) capable of ADP-ribosylating actin and a binding subunit (C2II) that is responsible for interaction with receptors on eukaryotic cells. Here we show that binding of C2 toxin depends on the presence of asparagine-linked carbohydrates. A recently identified Chinese hamster ovary cell mutant (Fritz, G., Schroeder, P., and Aktories, K. (1995) Infect. Immun. 63, 2334–2340) was found to be deficient inN-acetylglucosaminyltransferase I. C2 sensitivity of this mutant was restored by transfection of anN-acetylglucosaminyltransferase I cDNA. C2 toxin sensitivity was reduced after inhibition of α-mannosidase II. In contrast, Chinese hamster ovary cell mutants deficient in sialylated (Lec2) or galactosylated (Lec8) glycoconjugates showed an increase in toxin sensitivity compared with wild-type cells. Our results show that the GlcNAc residue linked β-1,2 to the α-1,3-mannose of the asparagine-linked core structure is essential for C2II binding to Chinese hamster ovary cells.