Pore-forming toxin

These toxins are potent but also highly specific to a limited range of target insects, making them safe biological control agents.

While the Bin toxin of Lysinibacillus sphaericus is able to form pores in artificial membranes[19] and mosquito cells in culture,[20] it also causes a series of other cellular changes including the uptake of toxin in recycling endosomes and the production of large, autophagic vesicles[21] and the ultimate cause of cell death may be apoptotic.

The portion entering the membrane, referred to as the head, is usually apolar and hydrophobic, this produces an energetically favorable insertion of the pore-forming toxin.

[3] Some β-PFTs such as clostridial ε-toxin and Clostridium perfringens enterotoxin (CPE) bind to the cell membrane via specific receptors – possibly certain claudins for CPE,[25] possibly GPI anchors or other sugars for ε-toxin – these receptors help raise the local concentration of the toxins, allowing oligomerisation and pore formation.

The BinB Toxin_10 component of the Lysinibacillus sphaericus Bin toxin specifically recognises a GPI anchored alpha glycosidase in the midgut of Culex[26] and Anopheles mosquitoes but not the related protein found in Aedes mosquitoes,[27] hence conferring specificity on the toxin.

Ions and small molecules, such as amino acids and nucleotides within the cell, flow out, and water from the surrounding tissue enters.

The loss of important small molecules to the cell can disrupt protein synthesis and other crucial cellular reactions.

In particular, nuclear - free erythrocytes under the influence of alpha-staphylotoxin undergo hemolysis with the loss of a large protein hemoglobin.

The A component then enters the cytosol and inhibits normal cell functions by one of the following means: ADP-ribosylation is a common enzymatic method used by different bacterial toxins from various species.

This can profoundly alter any sort of immune response, by inhibiting leucocyte proliferation, phagocytosis, and proinflammatory cytokine release.

[33] Electron microscopy studies of pneumolysin show that it assembles into large multimeric peripheral membrane complexes before undergoing a conformational change in which a group of α-helices in each monomer change into extended, amphipathic β-hairpins that span the membrane, in a manner reminiscent of α-haemolysin, albeit on a much larger scale (Fig 3).

[1][2][35] A family of highly conserved cholesterol-dependent cytolysins, closely related to perfringolysin from Clostridium perfringens are produced by bacteria from across the order Bacillales and include anthrolysin, alveolysin and sphaericolysin.

[26] Sphaericolysin has been shown to exhibit toxicity to a limited range of insects injected with the purified protein.