Animal Venoms as Potential Source of Anticonvulsants

Epilepsy affects millions of people worldwide, and there is an urgent need to develop safe and effective therapeutic agents. Animal venoms contain diverse bioactive compounds like proteins, peptides, and small molecules, which may possess medicinal properties against epilepsy. In recent years, research has shown that venoms from various organisms such as spiders, ants, bees, wasps, and conus snails have anticonvulsant and antiepileptic effects by targeting specific receptors and ion channels. This review underscores the significance of purified proteins and toxins from these sources as potential therapeutic agents for epilepsy. In conclusion, this review emphasizes the valuable role of animal venoms as a natural resource for further exploration in epilepsy treatment research.

Exaptation of two ancient immune proteins into a new dimeric pore-forming toxin in snails

The Membrane Attack Complex-Perforin (MACPF) family is ubiquitously found in all kingdoms. They have diverse cellular roles, however MACPFs with pore-forming toxic function in venoms and poisons are very rare in animals. Here we present the structure of PmPV2, a MACPF toxin from the poisonous apple snail eggs, that can affect the digestive and nervous systems of potential predators. We report the three-dimensional structure of PmPV2, at 17.2 Å resolution determined by negative-stain electron microscopy and its solution structure by small angle X-ray scattering (SAXS). We found that PV2s differ from nearly all MACPFs in two respects: it is a dimer in solution and protomers combine two immune proteins into an AB toxin. The MACPF chain is linked by a single disulfide bond to a tachylectin chain, and two heterodimers are arranged head-to-tail by non-covalent forces in the native protein. MACPF domain is fused with a putative new Ct-accessory domain exclusive to invertebrates. The tachylectin is a six-bladed β-propeller, similar to animal tectonins. We experimentally validated the predicted functions of both subunits and demonstrated for the first time that PV2s are true pore-forming toxins. The tachylectin "B" delivery subunit would bind to target membranes, and then the MACPF "A" toxic subunit would disrupt lipid bilayers forming large pores altering the plasma membrane conductance. These results indicate that PV2s toxicity evolved by linking two immune proteins where their combined preexisting functions gave rise to a new toxic entity with a novel role in defense against predation. This structure is an unparalleled example of protein exaptation.

First egg protein with a neurotoxic effect on mice

While many invertebrates sequester toxic compounds to endow eggs with chemical defences, here we show, for the first time to our knowledge, the identification of a neurotoxin of proteinaceous nature localized inside an egg. Egg extracts from the freshwater apple snail Pomacea canaliculata displayed a neurotoxic effect in mice upon intraperitoneal injection (i.p.) (LD50, 96h 2.3mg/kg). Egg protein and total lipids were analysed separately and the only fraction displaying a highly toxic effect (LD50, 96h 0.25mg/kg, i.p.) was further purified to homogeneity as an oligomeric glyco-lipoprotein of 400kDa and two subunits biochemically and immunologically indistinguishable from the previously described perivitellin PV2. The neurotoxin was heat sensitive and there was evidence of circulating antibody response to sublethal i.p. doses on mice. Clinical signs, histopathological and immunocytochemical studies revealed damage mostly in mice spinal cord. Experiments showed chromatolysis and a decreased response to calbindin D-28K associated with a significant increase of TUNEL-positive cells in the dorsal horn neurons. These results suggest that calcium buffering and apoptosis may play a role in the neurological disorders induced by the toxin in mammalian central nervous system. This is the first report of a mollusc neurotoxin genetically encoded outside the cone-snail species.

Structure–activity relationships of methoctramine-related polyamines as muscarinic antagonist: Effect of replacing the inner polymethylene chain with cyclic moieties

The aim of the present paper was to investigate the role of the octamethylene spacer of methoctramine (1) on the biological profile. Thus, this spacer was incorporated into a dianiline or dipiperidine moiety to determine whether flexibility and the basicity of the inner nitrogen atoms are important determinants of potency with respect to muscarinic receptors. The most potent compound was 4, which displayed, in the functional assays, a comparable potency at muscarinic M(2) receptors with respect to 1, and, in the binding assays, a loss of potency and selectivity toward muscarinic M(1) and M(3) receptor subtypes. Both compounds were endowed with antinociceptive activity. Furthermore, in microdialysis tests in rat parietal cortex, they enhanced acetylcholine release, most likely by antagonizing presynaptic muscarinic receptor subtypes.

Identification of a Novel Class of Nicotinic Receptor Antagonists

The venoms of predatory marine snails (Conus spp.) contain diverse mixtures of peptide toxins with high potency and selectivity for a variety of voltage-gated and ligand-gated ion channels. Here we describe the chemical and functional characterization of three novel conotoxins, alphaD-VxXIIA, alphaD-VxXIIB, and alphaD-VxXIIC, purified from the venom of Conus vexillum. Each toxin was observed as an approximately 11-kDa protein by LC/MS, size exclusion chromatography, and SDS-PAGE. After reduction, the peptide sequences were determined by Edman degradation chemistry and tandem MS. Combining the sequence data together with LC/MS and NMR data revealed that in solution these toxins are pseudo-homodimers of paired 47-50-residue peptides. The toxin subunits exhibited a novel arrangement of 10 conserved cystine residues, and additional post-translational modifications contributed heterogeneity to the proteins. Binding assays and two-electrode voltage clamp analyses showed that alphaD-VxXIIA, alphaD-VxXIIB, and alphaD-VxXIIC are potent inhibitors of nicotinic acetylcholine receptors (nAChRs) with selectivity for alpha7 and beta2 containing neuronal nAChR subtypes. These dimeric conotoxins represent a fifth and highly divergent structural class of conotoxins targeting nAChRs.