Synaptotagmin binding to botulinum neurotoxins

Botulinum neurotoxins (BoNTs) are exceptionally toxic proteins that cause paralysis, but are also extensively used as treatment for various medical conditions. Most BoNTs bind two receptors on neuronal cells, namely a ganglioside and a protein receptor. Differences in the sequence between the protein receptors from different species can impact the binding affinity and toxicity of the BoNTs. Here we have investigated how BoNT/B, /DC, and /G, all three toxins that utilize Synaptotagmin I and II (Syt-I/II) as their protein receptors, bind to Syt-I and-II from mouse/rat, bovine and human origin by isothermal titration calorimetry analysis. BoNT/G had the highest affinity to human Syt-I and BoNT/DC had the highest affinity for bovine Syt-II. As expected, BoNT/B, /DC and /G showed very low binding to human Syt-II. Furthermore, we carried out saturation difference transfer (STD) and STD-TOCSY NMR experiments that revealed the region of the Syt peptide in direct contact with BoNT/G, which demonstrate that BoNT/G ...