Molecular basis for disruption of E-cadherin adhesion by botulinum neurotoxin A complex

Abstract

How botulinum neurotoxins (BoNTs) cross the host intestinal epithelial barrier in foodborne botulism is poorly understood. Here, we present the crystal structure of a clostridial hemagglutinin (HA) complex of serotype BoNT/A bound to the cell adhesion protein E-cadherin at 2.4 Ångströms. The HA complex recognizes E-cadherin with high specificity involving extensive intermolecular interactions and also binds to carbohydrates on the cell surface. Binding of HA complex sequesters E-cadherin in the monomeric state thereby compromising the E-cadherin-mediated intercellular barrier and facilitating paracellular absorption of BoNT/A. We reconstituted the complete 14-subunit BoNT/A complex using recombinantly-produced components and demonstrated that abolishing either E-cadherin- or carbohydrate-binding of HA complex drastically reduces oral toxicity of BoNT/A complex in vivo. Together, these studies establish the molecular mechanism of how HAs contribute to the oral toxicity of BoNT/A.

Botulinum neurotoxins: new questions arising from structural biology

“…The 19S PTC may represent a dimer of 16S complexes. The HA complex interacts with carbohydrates through binding sites in HA1 and HA3, but not in HA2 [53,55,57,81], and via cadherin-1 binding to all three HA proteins [58]. The binding results in disruption of cell-cell adhesions between host intestinal epithelial cells.…”

Clostridial neurotoxins

“…A three-armed structure (i.e., like a triskelion) has been proposed, in which three HA70 molecules interact with a single NTNH molecule on one end, and each with a HA17/ HA33-dimer on the other (Figure 11.2) [80,100,101]. HA complexes interact with E-cadherin and impair intercellular junctions between enterocytes, thus facilitating the passage of BoNT complexes through the intestinal barrier via the paracellular route [100,102].…”

Structural Basis of the pH-Dependent Assembly of a Botulinum Neurotoxin Complex

“…The M-PTC is composed of BoNT and NTNHA. The L-PTC is a bimodular complex composed of the M-PTC and the HA complex, which is assembled by HA70, HA17, and HA33 and facilitates toxin absorption in the small intestine [9-14]. The structure of the LL-PTC is still largely unknown [15].…”