The fruiting bodies of fungi are known reservoirs for large quantities of pore forming proteins (PFPs). These PFP become active upon ingestion by unsuspecting insects or nematode species, where it is hypothesised that oligomerisation of the pore forming protein occurs in the mid-gut tissues leading to wide-spread tissue damage and ultimately killing of the insect or worm. One putative PFP that has recently been discovered from the mushroom Coprinopsis cinerea, is referred to here as coprinolysin (CC1G_11805). Coprinolysin is an aerolysin/ETX-like PFP which are characterised by formation of 2 - 3 nm sized ß-barrel pores in the respective target cells. These family members generally contain one or more domains responsible for the recognition of receptors or membranes and a seperate but common domain responsible for oligomerisation and pore formation.
Here, we determined the structure of a putative packaging assembly of coprinolysin which may resemble the state from the mushroom fruiting body. The assembly, arranged in this way, may ensure the delivery of high-concentrations of coprinolysin to the target tissue. Contrary to previous observations of nematocidal effect of coprinolysin, we have only identified toxic activity to insect cell lines (e.g. Spodoptera). While the mechanism of coprinolysin function remains elusive to date, we identified an aerolysin-like pre-pore assembly in two-subunits within the crystal structure which may suggest a mode of oligomerisation through the pore forming domain. We are now testing the hypothesis that coprinolysin is a bona fide pore forming protein by utilising a chimeric variant that has gained haemolytic activity. Taken together, these results suggest coprinolysin is an insect-targeting pore forming protein from the aerolysin/ETX-family.