ABSTRACT
Venoms of predatory marine cone snails are intensely studied because of the biomedical applications of the neuropeptides that they contain, termed conotoxins. Meanwhile some gastropod lineages have independently acquired secretory glands strikingly similar to the venom gland of cone snails, suggesting that they possess similar venoms. Here we focus on the most diversified of these clades, the genus Vexillum. Based on the analysis of a multi-species proteo-transcriptomic dataset, we show that Vexillum species indeed produce complex venoms dominated by highly diversified short cysteine-rich peptides, vexitoxins. Vexitoxins possess the same precursor organization, display overlapping cysteine frameworks and share several common post-translational modifications with conotoxins. Some vexitoxins show sequence similarity to conotoxins and adopt similar domain conformations, including a pharmacologically relevant inhibitory cysteine knot motif. The Vexillum envenomation gland (gL) is a notably more recent evolutionary novelty than the conoidean venom gland. Thus, we hypothesize lower divergence between vexitoxin genes, and their ancestral 'somatic' counterparts compared to that in conotoxins, and we find support for this hypothesis in the evolution of the vexitoxin cluster V027. We use this example to discuss how future studies on vexitoxins can inform the origin of conotoxins, and how they may help to address outstanding questions in venom evolution.
Subject(s)
Conotoxins , Conus Snail , Animals , Conotoxins/genetics , Conus Snail/chemistry , Conus Snail/genetics , Cysteine , Peptides/chemistry , Snails , VenomsABSTRACT
A new myzostome species, described here as Myzostoma khanhkhoaensis sp. nov., was collected in Nhatrang Bay, central Vietnam, during investigation of symbionts associated with crinoids. Myzostoma khanhkhoaensis sp. nov. was found only on Clarkcomanthus albinotus Rowe, Hoggett, Birtles Vail, 1986 in dense groups of up to 25 specimens. This species closely matches the colour pattern of the host by adjusting its cryptic colour and infects the distal part of crinoid arms, causing them to become curved. This is the first record of myzostomes that induce deformation of skeletal elements without the formation of galls or cysts. Morphologically M. khanhkhoaensis sp. nov. is close to M. cuniculus and M. pseudocuniculus but clearly differs from both of them by the shape of caudal blade and chaetae. Molecular-genetics analysis based on CO1, 16S and 18S DNA placed M. khanhkhoaensis sp. nov. in a clade including M. cuniculus, M. pseudocuniculus and M. indocuniculus.