Botulinum Toxin Complex Serotype B-Okra Exerts Oral Toxicity by Disrupting the Intestinal Epithelial Barrier

Botulinum toxin (BoNT) causes flaccid paralysis by blocking the release of neurotransmitters. BoNTs associate with neurotoxin-associated proteins (NAPs) to form a medium progenitor toxin complex (PTC) (M-PTC) and large PTC (L-PTC). The L-PTC serotype A-62A (L-PTC/A_62A) specifically targets intestinal M cells for invasion, whereas L-PTC serotype B-Okra (L-PTC/B_Okra), which exhibits higher oral toxicity, is mainly taken up by enterocytes. Hemagglutinin (HA) is a NAPs that promotes BoNT absorption from the intestine and has carbohydrate-binding and barrier-disrupting activities. In this study, we established an in vitro reconstitution and purification system for recombinant L-PTC/B_Okra and created a recombinant L-PTC/B_Okra mutant rL-PTC/BB-KA with carbohydrate-binding activity but not barrier-disrupting activity. rL-PTC/BB-KA significantly reduced the oral toxicity. Our results demonstrate that the toxin of B-Okra disrupts the epithelial barrier of enterocytes and exerts oral toxicity.