A camelid single-domain antibody neutralizes botulinum neurotoxin A by blocking host receptor binding

• Published in: Scientific reports 2017-08, Vol.7 (1), p.7438-12, Article 7438
• Main Authors: Yao, Guorui, Lam, Kwok-ho, Weisemann, Jasmin, Peng, Lisheng, Krez, Nadja, Perry, Kay, Shoemaker, Charles B., Dong, Min, Rummel, Andreas, Jin, Rongsheng
• Format: Article
• Language: English
• Subjects: 13/1; 13/106; 13/51; 14/19; 60 APPLIED LIFE SCIENCES; 631/535/1266; 692/699/255; 82/16; 82/29; 82/80; 82/83; Animals; Antibodies, Neutralizing - chemistry; Antibodies, Neutralizing - pharmacology; Antitoxins; BASIC BIOLOGICAL SCIENCES; Binding Sites; Botulinum toxin type A; Botulinum Toxins, Type A - chemistry; Botulinum Toxins, Type A - metabolism; Botulism; Camelidae - immunology; Clinical trials; Crystal structure; Crystallography, X-Ray; Food contamination; Gangliosides - metabolism; Humanities and Social Sciences; Immunoglobulin Heavy Chains - chemistry; Immunoglobulin Heavy Chains - pharmacology; Intoxication; Models, Molecular; Monoclonal antibodies; Motor neurons; multidisciplinary; Muscles; Nanobodies; Nerve Tissue Proteins - metabolism; Neurotoxins; Neurotransmitter release; Neutralization; Paralysis; Protein Binding; Protein Conformation; Rats; Science; Science (multidisciplinary); Serotypes; Single-Domain Antibodies - chemistry; Single-Domain Antibodies - pharmacology; Toxins
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-07457-5

Antibody treatment is currently the only available countermeasure for botulism, a fatal illness caused by flaccid paralysis of muscles due to botulinum neurotoxin (BoNT) intoxication. Among the seven major serotypes of BoNT/A-G, BoNT/A poses the most serious threat to humans because of its high potency and long duration of action. Prior to entering neurons and blocking neurotransmitter release, BoNT/A recognizes motoneurons via a dual-receptor binding process in which it engages both the neuron surface polysialoganglioside (PSG) and synaptic vesicle glycoprotein 2 (SV2). Previously, we identified a potent neutralizing antitoxin against BoNT/A1 termed ciA-C2, derived from a camelid heavy-chain-only antibody (VHH). In this study, we demonstrate that ciA-C2 prevents BoNT/A1 intoxication by inhibiting its binding to neuronal receptor SV2. Furthermore, we determined the crystal structure of ciA-C2 in complex with the receptor-binding domain of BoNT/A1 (H C A1) at 1.68 Å resolution. The structure revealed that ciA-C2 partially occupies the SV2-binding site on H C A1, causing direct interference of H C A1 interaction with both the N-glycan and peptide-moiety of SV2. Interestingly, this neutralization mechanism is similar to that of a monoclonal antibody in clinical trials, despite that ciA-C2 is more than 10-times smaller. Taken together, these results enlighten our understanding of BoNT/A1 interactions with its neuronal receptor, and further demonstrate that inhibiting toxin binding to the host receptor is an efficient countermeasure strategy.