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Proteomic interrogation of venom delivery in marine cone snails: novel insights into the role of the venom bulb.
Cone snails of the genus Conus are predatory marine gastropods mainly found in the shallow waters of the tropics and warm temperate seas. To prey on other marine organisms including fish, cone snails have evolved complex venoms synthesized and delivered by a highly sophisticated venom apparatus. Upon prey discovery, the venom is perfused through a harpoon-like radula tooth and rapidly injected into the prey to cause paralysis. While the venom components of cone snails have been intensively characterized, the mechanism of venom translocation and loading prior to and during injection remains elusive. The involvement of the venom bulb, a muscular dilation of the venom gland has been suggested, however evidence is sparse. Here, we use a combination of proteomics, molecular biology, and morphological examination to elucidate the potential role of the venom bulb in venom translocation and delivery. Analysis of the venom bulb proteome clearly demonstrated a function of this organ in muscular movement and, more interestingly, in burst muscle contraction. Morphological examination revealed high structural similarities to the mantle muscle of squids, animals known for their rapid escape response. We sequenced and further characterized arginine kinase, a key protein of rapid muscular movement in invertebrates and show high concentrations of this enzyme in the bulb when compared to the venom gland and the foot muscle. Proteins characteristic for venom biosynthesis were low in abundance. On the basis of our findings, we suggest that the bulb of cone snails is a highly specialized organ of venom translocation. Delivery of venom is driven by burst contractions of the bulb rapidly forcing the venom through the radula tooth into the prey.
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