# Towards Understanding the Function of Aegerolysins
## 2 Aegerolysins
### Fungal Aegerolysins from Ascomycotta--Eurotimyetes
#### 2.2.2 Aegerolyins from _Aspergillus niger_  
_Aspergillus niger_ van [PERSON] (_Eurotiales_) is a filamentous fungus that grows aerobically on organic matter. It is ubiquitous in soil and is commonly reported from indoor environments. _A. niger_ is capable of growing in a wide temperature range of 6-47 \({}^{\circ}\)C, with a relatively high temperature optimum at 35-37 \({}^{\circ}\)C, and it is capable of growing in an extremely wide pH range: 1.4-9.8 [24]. These capabilities and the abundant production of airborne condiospores result in a ubiquitous occurrence of the species, with a higher incidence in warm and humid locations. Although the main source of Black aspergillus is soil and litter, in compost they are among the most common fungi causing food spoilage and biological decay of other materials. _Aspergillus niger_ species complex is often responsible for the postharvest spoilage of fresh fruits (apples, pears, peaches, citrus fruits, grapes, figs, strawberries, tomatoes, melons, etc.) and some vegetables (especially onions, garlic, and sweet potatoes); they are also among the most common fungi isolated from dried fruits, beans, oilseeds, and nuts (peanuts, pecans, pistachios, hazelnuts, almonds, walnuts, etc.) [25; 26]. Because _A. niger_ has been in use already for many decades to produce extracellular (food) enzymes and citric acid, many of these product are considered generally recognized as safe (GRAS) by the United States Food and Drug Administration [24; 27]. Functional studies of the expression of the genes encoding the aegerolyins **NigA1** and **NigA2** and the MACPF-like proteins **NigB1** and **NigB2** suggest that the sporulation process is critical for the strong induction of the expression of all these genes. However, in laboratory environment, deletion of any of the aegerolysin genes had no effect on the growth, development, sporulation efficiency, and phenotype of the mutants, suggesting that aegerolysins are not key factors in the sporulation process [91]. In all expression studies, a strong correlation was observed between the expression of **NigA2** and **NigB1** genes [91]. In _Aspergillus_ species, aegerolysins were frequently found as secreted proteins. Their secretion was studied by secretion prediction and Western blotting, and it was confirmed that **NigA1** and **NigA2** are secreted by the fungus [91; 92]. Both nigerolysins A are leaderless proteins that reach the cell exterior by unconventional protein secretion [91; 92]. The subcellular localization of nigerolysins A in _A. niger_ was investigated by immunocytochemistry and live cell imaging. The **NigA** proteins are uniformly distributed in the cytoplasm of fungal hyphae [92]. **NigA2** was shown to interact specifically with an insect-specific membrane sphingolipid, CPE in combination with Chol, but not with SM/Chol [91]. Membranes of insect cells containing this specific sphingolipid were stained after binding the **NigA2** protein labeled with mCherry [91]. Detailed bioinformatics analysis of _Aspergillus_ asegerolysins suggests that the same function (target) likely occurs in only a limited number of aegerolysins. From the alignment, chromosomal loci analysis, orthology, synteny, and phylogeny, it appears that the same or similar function described for pairs of pesticidal proteins of _Pleurotus_ sp. also occurs in species of the subgenus Circumdati, section Nigri, series Nigri, and several other species with adjacent pairs of putative pesticidal proteins [92]. The combined results suggest that aegerolysins in _A. niger_, and probably in other aspergillus, may be involved in defense against predators. Of the two aegerolysins described in _A. niger_ strain CBS 513.88, **NigA2** also has a neighboring partner protein gene **NigB1**, whereas **NigA1** does not [92]. No variations in aegerolysin sequences for **NigA1** are observed in any of the nine other _A.