1.C.119 The Aegerolysin (Aegerolysin) Family
The aegerolysin protein family (from aegerolysin of the mushroom Agrocybe aegerita) comprises proteins of ∼15-20 kDa from various eukaryotic and bacterial taxa. Aegerolysins are distributed among fungal species, and variable numbers of homologs have been reported for species within the same genus. Some aegerolysins have been reported to be hemolytically active against mammalian erythrocytes. However, some function as bi-component proteins that have membrane activity in concert with another protein that contains a membrane attack complex/perforin domain (see TC# 1.C.97). The function of most of aegerolysins is unknown, although some have been suggested to play roles in organismal development. Potential biotechnological applications of aegerolysins have been discussed (Novak et al. 2015). Some mushroom aegerolysins, for example, can be used as markers to detect and label specific membrane lipids. Others can be used as biomarkers of fungal exposure, where their genes can serve as targets for detection of fungi and their progression during infectious diseases. Antibodies against aegerolysins can also be raised as immuno-diagnostic tools. Aegerolysins have been shown to serve as species determination tools for fungal phytopathogen isolates in terms of some closely related species, where commonly used internal transcribed spacer barcoding has failed. Strong promoters that regulate aegerolysin genes can promote secretion of heterologous proteins from fungi and have been successfully applied in simultaneous multi-gene expression techniques (Novak et al. 2015).
Aegerolysins, ostreolysin A (OlyA), pleurotolysin A (PlyA), and pleurotolysin B (PlyB) with the membrane-attack-complex/perforin domain are proteins from the mushroom genus Pleurotus. Upon binding to sphingomyelin/cholesterol-enriched membranes, OlyA and PlyA can recruit PlyB to form multimeric bi-component transmembrane pores. Pleurotus aegerolysins OlyA, PlyA2 and erylysin A (EryA) were shown to preferentially bind to artificial lipid membranes containing 50 mol% ceramide phosphoethanolamine (CPE), the main sphingolipid in invertebrate cell membranes. Panevska et al. 2019 found that OlyA6, PlyA2 and EryA bind to insect cells and to artificial lipid membranes with physiologically relevant CPE concentrations, and these aegerolysins permeabilize these membranes when combined with PlyB. These aegerolysin/PlyB complexes show selective toxicity toward western corn rootworm larvae and adults aswell as Colorado potato beetle larvae. Thus, these aegerolysin/PlyB complexes recognize CPE as their receptor molecule in the insect midgut. This mode of binding is different from those described for similar aegerolysin-based bacterial complexes and other Bacillus thuringiensis Cry toxins, which have protein receptors. Targeting of Pleurotus aegerolysins to CPE and formation of transmembrane pores in concert with PlyB suggest the use of aegerolysin/PlyB complexes as novel biopesticides for the control of western corn rootworm and Colorado potato beetle (Panevska et al. 2019). Aegerolysins play a role in promoting the entomopathogenic and antagonistic activity of B. bassiana, which is an active ingredient of bioinsecticides (Kraševec et al. 2021).