Abstact

Enterotoxigenic Bacteroides fragilis (ETBF) promotes colonic inflammation by secreting metalloenzyme toxins (BFTs). Understanding BFT mechanisms and developing neutralization strategies is critical. Here, we have solved the structures of BFT-1 and BFT-2, revealing that residue 357 in the active site of the catalytic domain explains the diversity of function observed in BFT subtypes. We demonstrate that BFTs can directly cleave human epithelial-cadherin at extracellular domain 4, with BFT-2 possessing the highest activity. Using an alpaca antibody library, we identified a single-domain antibody, Nb2.43, targeting the BFTs. Nb2.43 can neutralize all three subtypes of BFT by directly binding the metalloenzyme catalytic zinc ion with its CDR3 antigen-binding loop. Furthermore, Nb2.43 blocks cleavage of E-cadherin by BFT and prevents the damage caused by ETBF in vitro and in a mouse colitis model. This work provides structural insights into BFT diversity and delivers a therapeutic nanobody against ETBF-mediated inflammation.