A novel single-domain antibody obtained from immune Bactrian camels against botulinum toxin type A using SPR-based screening method.

Botulinum neurotoxin (BoNT) is a highly lethal toxin produced by the anaerobic bacterium Clostridium botulinum, which leads to nerve paralysis following poisoning. At present, there is no specific drug officially approved. Antibodies, particularly single-domain antibodies, represent safe and effective candidates for specific drugs against BoNT. In this study, the receptor-binding domain of botulinum toxin (BoNT/AHC(C)) was utilized to immunize Bactrian camels, resulting in the generation of a nanobody phage library. From this library, a high-affinity binding antibody, designated A1, and a neutralizing antibody, named HM, were successfully obtained through SPR-based screening. The affinity constant of HM for botulinum toxin is 1.08E-11 M. Results from computer simulations indicate that HM binds at the same site as SV2C. Furthermore, experimental findings demonstrate that HM exhibits significant blocking activity at both the in vitro binding level and the cellular level. In mouse toxicity experiments, HM has been shown to offer protection against a 20 LD(50) dose of BoNT/A. Consequently, HM mitigates botulinum toxin poisoning in mice by obstructing the binding of AHC(C) to SV2C.