This a trefoil C-terminal beta-rich domain found in PlyB, one of the components of pleurotolysin (Ply) pore-forming protein. Ply is a membrane attack complex/perforin-like family (MACPF) protein consisting of two components, PlyA and PlyB. PlyB and PlyA act together to form relatively small and regular pores in liposomes. The PlyB C-terminal trefoil sits on top of the PlyA dimer [1].

1: Conformational changes during pore formation by the perforin-related protein pleurotolysin. Lukoyanova N, Kondos SC, Farabella I, Law RH, Reboul CF, Caradoc-Davies TT, Spicer BA, Kleifeld O, Traore DA, Ekkel SM, Voskoboinik I, Trapani JA, Hatfaludi T, Oliver K, Hotze EM, Tweten RK, Whisstock JC, Topf M, Saibil HR, Dunstone MA; PLoS Biol. 2015;13:e1002049. PMID:25654333