1.C.5.1.1
ε-toxin (epsilon toxin; ETx) type B precursor, EtxB, of 328 aas.  Forms heptameric pores (Miyata et al. 2002).  However, it has been reported to act on oligodendrocytes causing demyelination without forming pores (Wioland et al. 2015). The toxin acts on the brain, affecting vascular permeability, but also damaging neurons, astrocytes and oligodendrocytes (Freedman et al. 2016). The pore-forming regions are initially folded up on the surfaces of the soluble precursors. To create the transmembrane pores, these regions must extend and refold into membrane-inserted beta-barrels (Tilley and Saibil 2006). The crystal structure of epsilon-toxin revealed structural similarity to aerolysin from Aeromonas hydrophila.(Cole et al. 2004). Residues in the central position of each beta-strand of the amphipathic beta-hairpin loop that forms the transmembrane pore, control the size and ion selectivity of the channel (Knapp et al. 2020). The pre-pore morphology of ETX) has been provided (Ji et al. 2023). The ETX pore is formed in two stages: ETX monomers first attach to the membrane and form a pre-pore with no special conditions required, which then undergo a conformational change to form a transmembrane pore at temperatures above the critical point in the presence of receptors (Ji et al. 2023). Epsilon toxin stimulates calcium-activated chloride channels, generating extracellular vesicles in Xenopus oocytes (Cases et al. 2024).