# Towards Understanding the Function of Aegerolysins
## 5 Lifestyle of Organisms Encoding for Aegerolysins and Putative Function of Aegerolysins
The molar ratio of lipids may be important. For some of aegerolysins an unknown protein receptor in the lipid membrane has been proposed, or for others binding was not studied. Different lipids or their combination may define the binding target of aegerolysins because different organisms have different composition of major membrane lipids, particularly the sphingolipids. Sphingolipids are a numerous and versatile group of lipids in eukaryote and in some bacterial taxa. These amphipathic molecules can be abundant components of cell membranes, and their sphingosine-based degradation products are involved in many physiological processes, including signaling [77]. One of the major sphingolipids in mammalian cell membranes that has been extensively studied is SM, which plays a central role in the formation of lipid rafts and ordered membrane domains, as well as cell signaling processes and regulation of plasma membrane and cholesterol homeostasis [77]. SM is also the major sphingolipid of nematode _C. elegans_. CPE is the major sphingolipid of _Oomycetes_, such as _Pythium ultimum_, _Phytophthora infestans_, and _P. capsici_, as well as of some flagellated protozoa, and the major sphingolipid in the lipid membranes of various invertebrates, including insects. In some invertebrates, CPE is combined with SM, such as mosquitoes _Aedes aegypti_,Culex quinquefuscatus_, or moths as _Manduca sexta_. In some _Bacteroidetes_, CPE is combined with ceramide phosphoglycerol, such as in _Flectobacillus major_ and _Bacteroides fragilis_. CAEP is a CPE analog of aquatic invertebrates, such as mollusks and cnidarians [77]. The aegerolysiss appear to have a (different?) function(s) associated with the specific stage of their development; it seems possible that they serve the interaction between organisms in the environment. Based on their sequence and binding diversity, it appears that these proteins might serve to scan the membranes of potential competitors or hosts in the niche. After binding to a specific lipid or lipid combination, or to yet unknown proteins receptors in lipid membranes, some of them may serve to dock various partner proteins from the organism of origin or perhaps from the target organism after the proteolytic cleavage. It appears that aegerolysiss represent a part of adaptive response to the environment, by sensing lipid components of organisms in their environment and excluding competitors by forming two-component pores as a kind of primitive \"immune interaction.\" Some partner proteins have a similar (MACPF) fold to some molecules, such as MPEG-1, or proteins C8 and C9, which are involved in the formation of a heterologimeric protein-membrane attack complex (MAC), and have a function in mammalian immune defense [126; 127]. It is possible that organisms such as hemibiotrophic plant pathogen _Moniliophthora pernicosa_ can increase their flexibility in lipid sensing with additional copies (six) of aegerolysin genes (if differently expressed). Horizontal gene transfer often plays a role in shaping the mechanisms by which a pathogen evades, counteracts, mimics, subverts, and manipulates the host [174]. Plasmidencoded genes for aegerolyins and partner proteins of the ubiquitous, aerobic, and sporeforming organism, such as _B. thuringiensis_, which is an opportunistic pathogen for very diverse hosts, including vertebrates, plants, insects, nematodes, mollusks, protozoa, animal and human parasites, appear to be particularly susceptible to their dissemination. Especially in combination with pore formation, which may facilitate the presence or uptake of heterologous DNA molecules or their parts present in the environment. It is also known that _B. thuringiensis_ harbors a variety of transposable elements, including insertion sequences and transposons [139; 175]. In addition, it has been already shown that partial genes can serve as a source of novel Cry toxins [176]. Other possible vectors are (DNA) viruses.