# Towards Understanding the Function of Aegerolysins
## 2 Aegerolysins
### Fungal Aegerolysins from Basidiomycota--Agaricomycotina  
#### 2.1.1. Aegerolysins from Pleurotus ostreatus  
The oyster mushroom or hiratake, Pleurotus ostreatus (Jacq. ex Fr.) [PERSON]. (1871) (_Agaricales_), is widely distributed in many temperate and subtropical forests. As a saprotroph, a white-rot wood fungus, it is a primary decomposer of wood, especially deciduous trees such as beech. It is also known to paralyze nematodes and consume prey [15]. As a common edible mushroom, it is grown commercially for food throughout the world. Eleurotolysin A (**PlyA**, **PriA**), ostreolysin (**OlyA**), ostereolysin A6 (**OlyA**), recombinant ostreolysin (**rOlyA**), are aegerolysins from the mushroom _P. ostreatus_. According to genome sequences of _P. ostreatus_ strains PC9 and PC15, they are encoded by the same locus [52; 53; 54; 55; 56]. In 1979, it was discovered that _P. ostreatus_ encodes the hemolytic protein pleurotolysin with a size of 15 kDa, and these first experiments showed the importance of sphingomyelin (SM) for **Ply** binding [57]. A clone containing aegerolysin gene was the most abundant expressed sequence tag (EST) in the primordial and the fruit body library [58]. Then, 25 years later, in 2004, it was revealed that this **Ply** protein is actually composed of subunits A and B [59]. Component A (**PlyA**), a 15 kDa aegerolysin, binds to SM/cholesterol (Chol)-rich membranes and then recruits a 59 kDa membrane attack complex/perforin (MACPF)-domain containing protein partner, **PlyB**, which then leads to transmembrane pore formation and cell lysis [59]. The combination of X-ray diffraction and cryo-electron microscopy has shown that **PlyA** paired with **PlyB** forms a 39-heteromeric membrane-embedded pore with a 13-fold symmetry structure (PDB ID: 4V2T) (Figure 1) [60]. **PlyA** has a \(\beta\)-sandwich structure similar to the actinoporin family (PF06369) of pore-forming proteins [60]. For adequate binding of **PlyA**, the Chol content should be more than 30 mol% [59]. **PlyA**/**PlyB** nanopores have been recently proposed as sequencing tools [61]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Organism Name** & **Other Names** & **Taxonomy** & **Lifestyle/Niche** & **Reference** \\ \hline \multirow{3}{*}{_Acaligenes faecalis_} & & & Soil, water, environments & \\  & & & associated with humans & \\  & & & Human opportunistic pathogen & \\  & & & Nematoidal & \\ \hline \multirow{3}{*}{_Pseudomonas aeruginosa_} & & & Ubiquitous opportunistic pathogen on: & \\  & & & humans, vertebrates, plants, and & \\  & & & insects & \\ \hline \multirow{3}{*}{_Chrysodeixis includes_} & \multirow{3}{*}{_Pseudolplasia includes_} & \multirow{3}{*}{_Lepidoptera_} & Plant pest (defoliator) & \\  & & & _Nocutiidae_ & Larvae feed on a wide range of & \\  & & & plants & \\ \hline \multicolumn{5}{c}{**Viria**} \\ \hline \multirow{3}{*}{_Trichophusia ni_ ascovirus 6a1} & \multirow{3}{*}{_Trichoplasia ni_ ascovirus 2c_} & _Varidnaviria_ & Obligate pathogen & \\  & & _Ascoviridae_ & _P. includes_ moth larvae & [47; 49; 50; 51] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._In 2002, another group of researchers isolated a very similar 15 kDa protein from the same mushroom and named it ostreolysin (**Oly**) [63]. The primary structure of **Oly** is 79% (29 amino acids substitution) identical to **PlyA**[11]. The first experiments with the native isolate of **Oly** showed that it is cytolytic for erythrocytes and various cell lines [64; 65]. Since the expression of **Oly** occurs during the formation of primordia and fruiting bodies of the mushroom, it has been speculated that it plays a role in the fruiting bodies of the mushroom [63; 66; 67]. Biochemical experiments in 2004 showed that **Oly** also specifically recognizes membranes enriched in SM and Chol [68; 69], and that binding of a protein is abolished after pretreatment of cells with methyl-\(\beta\)-cyclodextrintr or lysophospholipids [70; 71].