Cone snails are marine gastropods which utilize their venom to hunt prey and defend against predators [1]. The majority of the venom is comprised of small toxic peptides named conotoxins, which target membrane receptors, while a smaller part of the venom contains larger proteins, which are thought to be involved in conotoxin maturation and in the envenomation process [2]. Interestingly, many species express conoporins, which are similar to actinoporins, pore-forming toxins from sea anemones [3]. Since conoporins were found to be highly expressed in the venom gland of many cone snail species, they are thought to play an important part in the envenomation process. Despite this, the exact function of conoporins remains unknown. We propose four hypotheses regarding the biological role of conoporins, those being (i) permeabilization of epithelial barriers, (ii) facilitating membrane translocation of conotoxins through pores, (iii) antimicrobial activity, and (iv) aiding in digestion.
We have performed a thorough bioinformatic search for conoporins and obtained 95 unique sequences from 27 cone snail species. Similar to other molluscan actinoporin-like proteins, conoporins differ from typical actinoporins by containing extensions at the N- and C-termini, while the structure of the central β-sandwich appears to be conserved [4,5]. Furthermore, when analyzed on a phylogenetic tree, the full-length sequences of conoporins appear to form at least three distinct clades. Until now, we have successfully expressed and isolated three conoporins, two from the piscivorous Conus magus (ConM3 and ConM6) and one from the vermivorous Conus ebraeus (ConEb1). Our preliminary results show that ConM3 exerts hemolytic activity on bovine erythrocytes, while ConM6 and ConEb1 do not. Interestingly, using cryo-electron microscopy, we observed that ConEb1 forms hexameric oligomers when incubated with large unilamellar vesicles comprised of a 1:1 ratio of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and sphingomyelin.