Mechanism of botulinum neurotoxin B and G entry into hippocampal neurons.
Botulinum neurotoxins (BoNTs) target presynaptic nerve terminals by recognizing specific neuronal surface receptors. Two homologous synaptic vesicle membrane proteins, synaptotagmins (Syts) I and II, bind toxins BoNT/B and G. However, a direct demonstration that Syts I/II mediate toxin binding and entry into neurons is lacking. We report that BoNT/B and G fail to bind and enter hippocampal neurons cultured from Syt I knockout mice. Wild-type Syts I and II (but not Syt I loss-of-function toxin-binding domain mutants) restored binding and entry of BoNT/B and G in Syt I-null neurons, thus demonstrating that Syts I/II are protein receptors for BoNT/B and G. Furthermore, mice lacking complex gangliosides exhibit reduced sensitivity to BoNT/G, and binding and entry of BoNT/A, B, and G into hippocampal neurons lacking gangliosides is diminished. These data suggest that gangliosides are the shared coreceptor for BoNT/A, B, and G, supporting a double-receptor model for these three BoNTs for which the protein receptors are known.
D000818:Animals; D001905:Botulinum Toxins / Q000378:metabolism* / Q000494:pharmacology; D019274:Botulinum Toxins, Type A; D002478:Cells, Cultured; D005732:Gangliosides / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D050863:Synaptotagmin I / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D050861:Synaptotagmin II / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
D005732:Gangliosides; D008024:Ligands; D011956:Receptors, Cell Surface; D050863:Synaptotagmin I; D050861:Synaptotagmin II; C494311:Syt1 protein, mouse; C494263:Syt2 protein, mouse; C096323:rimabotulinumtoxinB; C488535:botulinum toxin type G; D001905:Botulinum Toxins; D019274:Botulinum Toxins, Type A