pore-forming module of Clostridium perfringens epsilon-toxin and similar aerolysin-type beta-barrel pore-forming proteins
Clostridium perfringens epsilon-toxin is responsible for fatal enterotoxemia in ungulates. It forms a heptamer in the lipid rafts of Madin-Darby Canine Kidney (MDCK) cells, leading to cell death; its oligomer formation is induced by activation of neutral sphingomyelinase. This group also includes an insecticidal crystal protein Cry14-4 (encoded on plasmid pBMBt1 of Bacillus thuringiensis serovar darmstadiensis). Also included is pXO2-60 (a protein from the pathogenic pXO2 plasmid of Bacillus anthracis) which harbors a unique ubiquitin-like fold domain at the C-terminus of the aerolysin-like domain, and is involved in virulence. They belong to the aerolysin family of beta-pore-forming proteins (beta-PFPs). PFPs are generally secreted as water-soluble monomers, which upon binding to target lipid membranes, oligomerize and form transmembrane pores harmful to cells. Beta-PFPs form pores by transmembrane beta-barrels. Aerolysin-type beta-PFPs are believed to use an amphipathic beta-hairpin to form the beta-barrel, are found in all kingdoms of life and many are bacterial toxins. In addition to having a role in microbial infection, they have potential as biotechnological sensors and delivery systems. They share a similar monomeric architecture, with a variable membrane-binding domain and a structurally conserved pore-forming region. A significant portion of the monomeric subunit structure is re-organized to form the pore. Oligomers formed by members of the aerolysin family include: hepta- (aerolysin), octa- (Dln1), and nonameric oligomers (lysenin and monalysin).
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