C. perfringens enterotoxin-claudin pore complex: Models for structure, mechanism of pore assembly and cation permeability
The pore-forming Clostridium perfringens enterotoxin (CPE), a common cause of foodborne diseases, facilitates Ca2+ influx in enterocytes, leading to cell damage. Upon binding to certain claudins (e.g. claudin-4), CPE forms oligomeric pores in the cell membrane. While the CPE-claudin interaction mechanism is well known, the structure and assembly of the pore complex remain elusive. Here, using AlphaFold2 complex prediction, structure alignment, and molecular dynamics simulations, we generated models of pre-pore and pore states of the CPE-claudin-4 complex sequentially addressing CPE-claudin, CPE-CPE, and claudin-claudin interactions, along with CPE conformational changes. The CPE pore is a hexameric variation of the typically heptameric pore stem and cap architecture of aerolysin-like {beta}-barrel pore-forming toxins ({beta}-PFT). The pore is lined with three hexa-glutamate rings, which differs from other {beta}-PFTs and confers CPE-specific cation selectivity of the pore. Additionally, the pore center is indicated to be anchored by a dodecameric claudin ring formed by a cis-interaction variant of an interface found in claudin-based tight junction strands. Mutation of an interfacial residue inhibited CPE-mediated cell damage in vitro. We propose that this claudin ring constitutes an anchor for a twisting mechanism that drives extension and membrane insertion of the CPE {beta}-hairpins. Our pore model agrees with previous key experimental data providing insights into the structural mechanisms of CPE-mediated cytotoxic cation influx.