# Towards Understanding the Function of Aegerolysins
## 2 Aegerolysins
### Fungal Aegerolysins from Basidiomycota--Agaricomycotina
#### 2.1.2 Aegerolysins from _Pleurotus eryngii_  
Boletus of the steppes _Pleurotus eryngii_ (DC.) Quel. 1872 (_Agaricales_), commonly called king oyster or trumpet or brown mushroom, French horn mushroom, or Ali'i oyster, is an edible mushroom. It is of commercial interest because of the mild taste and pleasant odor of its fruiting bodies. In addition, its mycelium is often grown on lignocellulosic wastes (such as wheat straw). Unlike _P. ostreatus_, this fungus lives saprobically or facultatively biotrophic on roots of herbaceous plants of the _Apiaceae_ family as a grassland-litter decomposer. _Pleurotus eryngii sensu stricto_ consists of at least five varieties such as var. _eryngii_, _ferulae_, _aleaeselini_, _thapsiae_, and _tingitanus_, which differ significantly in their habitat distribution, host, and morphology [16]. It possesses nematocidal properties as well as _P. ostreatus_[15]. Pleurotolysin A2 (**PlyA2**) and erylysim (**EryA**) are two aegerolysins from _P. eryngii_. In 2006, a 17-kDa hemolysis was isolated from fruiting bodies of the mushroom _P. eryngii_ and was originally named eryngeolysin [93]. Its N-terminal sequence showed high homology to **OlyA** from _P. ostreatus_ and aegerolysin from _Agrocybe aegerita_. Its hemolytic activity remained unchanged over the pH range of 4 to 12. It also showed antibacterial activity against _Bacillus megaterium_ and _B. subtilis_, but not against some other bacteria such as _Staphylococcus aureus_, _Escherichia coli_, _Enterobacter aerogenes_, _Pseudomonas aeruginosa_, _P. fluorescens_, _Mycobacterium pllei_, and _Proteus vulgaris_, or fungal species _Botrytis cinerea_, _Fusarium oxysporum_, _Mycosphaarella arachidicola_, _Phyalsospora piricola_, and _Rhizoctonia solani_[93]. The sensitivity of mammalian erythrocytes to eryngeolysis was the highest, followed by birds, reptiles, and fish erythrocytes [93]. It also showed cytotoxicity against leukemia cells (L1210), and inhibited mitogenic responses of mouse splenocytes. N-glycolyneuraminic acid was the only sugar that could inhibit hemolytic activity [93]. In 2013, the sedimentation assay of the crude extract of _P. erygii_ revealed that pleurotolysin A2 (**PlyA2**) is also a SM/Chol-binding protein [94]. **PlyA2** has two amino acid substitutions compared to **PlyA**[95], while it has 93% sequence identity (nine substitutions) with **OlyA6**[94]. Since the recombinant protein showed no hemolytic activity or toxicity to Hela cells it was then prepared as recombinant fluorescently labeled protein, **PlyA2**-EGFP, which was used as a lipid raft marker. **PlyA2** successfully labeled Hela cells, and binding of the protein was abolished after the pretreatment of the cells with methyl-\(\beta\)-cyclodextrintrim or sphingomyelinase. **PlyA2**-EGFP showed substantial colocalization with the raft-associated protein CD59. After permeabilization of the cells, **PlyA2** was found to bind to late endosomes and, similar to **OlyA6**, not to cytoplasm-facing membranes. As with **OlyA6**, **PlyA2** was later shown to bind more strongly to CPE/Chol-containing membranes [80]. Interestingly, **PlyA2** was also able to recognize and bind CPE membranes in the absence of Chol, as the only of the tested _Pleurotus_ aegerolysins [80]. **PlyA2**-EGFP successfully labeled CPE in _Drosophila_ embryonic Kc167 cells and in larvae of the same insects [80]. It is suggested that **PlyA2**/**PlyB** complexes can be used as new bioinsecticides, as has been discussed for **OlyA6**/**PlyB** complexes [79]. A novel bicomponent toxin pair was isolated and characterized from _P. erygii_, **EryA** and **EryB** in 2010 [96]. Most _Pleirotus_ aegerolysis (**OlyA**, **OlyA6**, **PlyA**, and **PlyA2**) bind to SM/Chol-rich lipid membranes [5; 59; 65; 74; 97; 94], but not **EryA**, ortholog of **PlyA2** from _P. eriygii_[80]. For this reason **EryA**-mCherry was very recently used as a molecular tool for detection of periodontal disease which is in majority of the cases associated with CPE-producing periodontal bacteria [98].