The Botulinum toxin type A disulfide bonded heavy chain - light chain heterodimer (botA HC:LC, encoded by the C. botulinum botA gene) (Lacy et al. 1998) binds ganglioside GT1b and synaptic vesicle protein 2A (SV2A) on the plasma membrane of a human target cell. In vivo, this process specifically targets synapses at neuromuscular junctions, where toxin association with ganglioside may position it to bind efficiently to SV2A, SV2B, or SV2C when those proteins are exposed at the cell surface by exocytosis (Dong et al. 2006). In vitro, botA HC:LC can bind gangliosides in addition to GT1b but with lower affinity (Kozaki et al. 1998). Only GT1b binding is annotated here.