Peptide ion channel toxins from the bootlace worm, the longest animal on Earth

Abstract

Polypeptides from animal venoms have found important uses as drugs, pharmacological tools, and within biotechnological and agricultural applications. We here report a novel family of cystine knot peptides from nemertean worms, with potent activity on voltage-gated sodium channels. These toxins, named the α-nemertides, were discovered in the epidermal mucus of Lineus longissimus, the ‘bootlace worm’ known as the longest animal on earth. The most abundant peptide, the 31-residue long α-1, was isolated, synthesized, and its 3D NMR structure determined. Transcriptome analysis including 17 species revealed eight α-nemertides, mainly distributed in the genus Lineus. α-1 caused paralysis and death in green crabs (Carcinus maenas) at 1 µg/kg (~300 pmol/kg). It showed profound effect on invertebrate voltage-gated sodium channels (e.g. Blattella germanica Nav1) at low nanomolar concentrations. Strong selectivity for insect over human sodium channels indicates that α-nemertides can be promising candidates for development of bioinsecticidal agents.

The Toxins of Nemertean Worms

“…However, it indicates that there is much yet to discover. This is further stressed by the aforementioned recent study by Jacobsson et al [ 120 ], who performed analyses of 17 transcriptomes, some of which are previously reported [ 119 , 124 , 130 ]. This analysis revealed seven novel α-nemertides, eight novel β-nemertide sequences (neurotoxin B-analogs), and 29 parborlysin related sequences.…”

“…No TTX could be identified, although the mucus was shown to be highly toxic to crustaceans [ 25 ]. Instead, the size exclusion of mucus from L. longissimus and subsequent UPLC-MS analysis led to the discovery of one peptide (named nemertide ß-1) closely resembling neurotoxin B-IV, and importantly, two peptides of lower mass (3308 and 3360, respectively) [ 120 ]. Although the relationship is not conclusive, these α-nemertides, as they were called, bear resemblance both in the size and toxicity to Bacq’s nemertine, as well as the Lineus peptides that were discovered by Kem.…”

“…The Whelan transcriptome study [ 124 ] demonstrated the presence of a number of putative toxin sequences in Malacobdella grossa , such as neoverrucotin subunit beta, a pseudechetoxin-like cysteine-rich venom protein, and plancitoxin-1. M. grossa has been the subject of study for toxin content in some other studies: the trancriptome analysis by Jacobsson et al [ 120 ] did not indicated the presence of either alpha- or beta-nemertide and neither parborlysin sequences. Neither was Kem et al able to find pyridine alkaloids in M. grossa [ 5 , 17 ], and TTX also appears to be absent [ 80 ].…”

“…As the arsenal of nemertean peptide toxins is growing, a comment on nomenclature is warranted. We have introduced the term nemertide [ 120 ] and propose that this could be employed as a general term for nemertean peptide toxins; Greek prefixes are then used to indicate families. Thus, the α-nemertides is used for the family of 3 kDa cystine knot neurotoxins, and we argue that the ß-nemertides (6 kDa), in effect, can be viewed as a part of the same family as the neurotoxins BI to BIV.…”

Compound Heterozygous SCN5A Mutations in Severe Sodium Channelopathy With Brugada Syndrome: A Case Report

“…As this patient's severe phenotype seems to be associated with Na v 1.5-F1571L displaying a hyperpolarizing shift in the voltage dependence of inactivation, we explored if we could restore the variant's voltage dependence of inactivation toward WT values by drug/toxin addition. The peptide toxin nemertide α-1 seemed to be a good candidate as it was reported to have a decelerating effect on the inactivation process of human sodium channels without influencing the parameters of activation and I Na density ( 17 ). Two minutes of perfusion of 5 μM of nemertide α-1 induced a steady-state modification of I Na inactivation of both Na v 1.5 + β 1 and the variant p.F1571L + β 1 ( Figure 4A ).…”