1.C.97.1.1
Pleurotolysin A/B pore-forming toxin. Pleurotolysin A (PlyA; also called ostreolysin A, OlyA) binds first in a sphingomyelin-dependent process; Pleurotolysin B (PlyS) binds to A in the membrane and inserts (Kondos et al., 2011).  The binary cytolytic pore-forming complex forms non-selective ion conducting pores of variable size (Schlumberger et al. 2013) to promote fruiting (Ota et al. 2014). Conformational changes accompanying pore formation have been reported (Lukoyanova et al. 2015).   In these systems, the aegerolysin-like proteins provide the membrane cholesterol/sphingomyelin selectivity and recruit oligomerised pleurotolysin B molecules, to create a membrane-inserted pore complex. The resulting protein structure has been imaged with electron microscopy, and it has a 13-meric rosette-like structure, with a central lumen that is ~4-5 nm in diameter. The opened transmembrane pore is non-selectively permeable for ions and smaller neutral solutes, and is a cause of cytolysis of a colloid-osmotic type (Ota et al. 2014). Ostreolysin A6 (OlyA6) is a protein produced by the oyster mushroom (Pleurotus ostreatus). It binds to membrane sphingomyelin/cholesterol domains, and together with its protein partner, pleurotolysin B (PlyB), it forms 13-meric transmembrane pore complexes. OlyA6 binds 1000 times more strongly to the insect-specific membrane sphingolipid, ceramide phosphoethanolamine (CPE). In concert with PlyB, OlyA6 has potent and selective insecticidal activity against the western corn rootworm. Milijaš Jotić et al. 2021 analysed the histological alterations of the midgut wall columnar epithelium of western corn rootworm larvae fed with OlyA6/PlyB, which showed vacuolisation of the cell cytoplasm, swelling of the apical cell surface into the gut lumen, and delamination of the basal lamina underlying the epithelium. Cryo-EM was used to explore the membrane interactions of the OlyA6/PlyB complex using lipid vesicles composed of artificial lipids containing CPE, and western corn rootworm brush border membrane vesicles. Multimeric transmembrane pores were formed in both vesicle preparations, similar to those described for sphingomyelin/cholesterol membranes. Thus, the molecular mechanism of insecticidal action of OlyA6/PlyB arises from specific interactions of OlyA6 with CPE, and the consequent formation of transmembrane pores in the insect midgut (Milijaš Jotić et al. 2021).