This domain is found in Monalysin Pore-forming Toxin which is a type of beta-barrel pore-forming toxin protein found in Pseudomonas entomophila. Monalysin forms a stable doughnut-like 18-mer complex composed of two disk-shaped nonamers to form a pore. The domain is composed of a central twisted beta -sheet composed of three antiparallel beta-strands (beta 3, beta 6, and beta 8/9) and flanked by the pore-forming segment and the C-terminal region on either side. The pore-forming domain (residues 102-170) is located between strands beta 3 and beta 6, and is formed from two antiparallel beta-strands connected by three alpha-helices, alpha 3, alpha 4, and alpha 5. The C-terminal region forms a long alpha-helix followed by a small hairpin and a short alpha-helix [1].

1: X-ray and Cryo-electron Microscopy Structures of Monalysin Pore-forming Toxin Reveal Multimerization of the Pro-form. Leone P, Bebeacua C, Opota O, Kellenberger C, Klaholz B, Orlov I, Cambillau C, Lemaitre B, Roussel A; J Biol Chem. 2015;290:13191-13201. PMID:25847242