longissimus, and Lineus ruber), Palaeonemertea ( Cephalothrix hongkongiensis, Cephalothrix linearis, and Tubulanus polymorphus) and Hoplonemertea ( Malacobdella grossa and Paranemertes peregrina). These toxins were identified in all nine species, representing all three nemertean classes: Pilidiophora ( Cerebratulus marginatus, Lineus lacteus, L. A whole-animal transcriptomic toxin-profiling study of nine nemertean species revealed several transcripts that match known toxin families from other venomous animals, especially sequences similar to plancitoxin from the crown-of-thorns sea star. These mucosal toxins may be utilized simultaneously for defense and predation without a clear separation of roles.įew studies have attempted to mine genome or transcriptome data to identify known nemertean toxins and potential novel variants. Furthermore, nemerteans produce a characteristic mucus layer (as with many marine organisms), and this also contains toxins, which are probably delivered passively as a poison or toxungen. Instead, glandular cells that are thought to secrete toxins are distributed throughout the proboscis. The limited understanding of nemertean toxins in part reflects the absence of a centralized venom system with a distinct venom gland and venom duct that can be milked or dissected easily. These toxins have been discussed in a comprehensive review. Comprehensive sequence, structural and pharmacological data are only available for a handful of proteins from three species in the class Pilidiophora: Cerebratulus lacteus (cytotoxin A-III and neurotoxins B-II and B-IV), Parborlasia corrugatus (parbolysin), and Lineus longissimus (nemertides α-1, α-2 and β-1). Few peptide or protein components have been isolated, expressed and characterized in terms of structure and activity. Nemertean toxins were first discovered in the epidermal mucus and research has focused on small-molecule components, such as tetrodotoxin and other alkaloids. Habitus of Amphiporus lactifloreus ( A) with a magnified stylet apparatus ( B, C). Nemerteans can therefore be included along with cnidarians, echinoderms and polychaetes as another ancient marine lineage that produces neurotoxins for defense and/or predation. Nemerteans are typically carnivorous predators or scavengers and several species hunt well-defended and, in some cases, venomous species, such as polychaetes, although their ecology and feeding habits are not yet understood in detail. Having attacked and retreated, the predator later returns to its immobilized prey in order to feed.
#Protein scaffold mollusk full
Hoplonemerteans probably use the proboscis tip to facilitate the injection of venom during fast strikes, leading to full paralysis within a few minutes. All three feature an eversible proboscis, but hoplonemerteans uniquely possess a hardened needle-like proboscis tip that can pierce the prey cuticle, as shown for the topic of this study: Amphiporus lactifloreus ( Figure 1). A recently-proposed system has established three nemertean classes: Paleonemertea, Pilidiophora and Hoplonemertea. It belongs to the disputed superphylum Lophotrochozoa, which contains one third of all marine animals, including sensu stricto polychaetes, mollusks, brachiopods and phoronids. Nemertea is a phylum of unsegmented worms (ribbon worms) featuring 1300 mostly marine species. Our findings provide insight into the largely overlooked venom system of nemerteans and support a hypothesis in which the nemertean proboscis evolved in several steps from a flesh-melting organ in scavenging nemerteans to a flesh-melting and toxin-secreting venom apparatus in hunting hoplonemerteans. Two new nemertean-typical toxin candidates could be described and were named U-nemertotoxin-1 and U-nemertotoxin-2. Some of these products were also directly identified in the mucus proteome, supporting their preliminary identification as secreted toxin components. No variants were found of known nemertean-specific toxin proteins (neurotoxins, cytotoxins, parbolysins or nemertides) but several toxin-like transcripts were discovered, expressed strongly in the proboscis, including putative metalloproteinases and sequences resembling sea anemone actitoxins, crown-of-thorn sea star plancitoxins, and multiple classes of inhibitor cystine knot/knottin family proteins. We carried out a preliminary proteotranscriptomic analysis of putative toxins produced by the hoplonemertean Amphiporus lactifloreus (Hoplonemertea, Amphiporidae). Nemerteans (ribbon worms) employ toxins to subdue their prey, but research thus far has focused on the small-molecule components of mucus secretions and few protein toxins have been characterized.
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