Cryo-EM Structures of Clostridium perfringens Enterotoxin Bound to its Human Receptor, Claudin-4

Pathogenic strains of Clostridium perfringens secrete an enterotoxin (CpE) that causes prevalent, severe, and sometimes deadly gastrointestinal disorders in humans and domesticated animals. CpE binds selectively to membrane protein receptors called claudins on the apical surfaces of small intestinal epithelium. Claudins normally construct tight junctions that regulate epithelial paracellular transport but are hijacked from doing so by CpE and are instead led to form claudin/CpE "small complexes". Small complexes are building blocks for assembling oligomeric {beta}-barrel pores that penetrate the plasma membrane and induce gut cytotoxicity. Here we present structures of CpE in complexes with its native claudin receptor in humans, claudin-4, at 4.0 and 2.8 [A] using cryogenic electron microscopy. The structures reveal the overall architecture of the small complex, that the small complex can be kinetically trapped, and resolve its key features; like the residues used in claudin/CpE complex binding, the orientation of CpE relative to the membrane, and CpE-induced structural changes to claudin-4. Further, the structures allude to the biophysical procession from small complex to cytotoxic {beta}-barrel pore used by CpE during pathogenesis and the role of trypsin in this process. In full, this work elucidates the structure and mechanism of claudin-bound CpE pore assembly and provides strategies to obstruct its formation to treat CpE-induced gastrointestinal diseases.