alpha-Latrotoxin affects mitochondrial potential and synaptic vesicle proton gradient of nerve terminals

Alpha-latrotoxin rescues SNAP-25 from BoNT/A-mediated proteolysis in embryonic stem cell-derived neurons

The botulinum neurotoxins (BoNTs) exhibit zinc-dependent proteolytic activity against members of the core synaptic membrane fusion complex, preventing neurotransmitter release and resulting in neuromuscular paralysis. No pharmacologic therapies have been identified that clinically relieve botulinum poisoning. The black widow spider venom α-latrotoxin (LTX) has the potential to attenuate the severity or duration of BoNT-induced paralysis in neurons via the induction of synaptic degeneration and remodeling. The potential for LTX to antagonize botulinum poisoning was evaluated in embryonic stem cell-derived neurons (ESNs), using a novel screening assay designed around the kinetics of BoNT/A activation. Exposure of ESNs to 400 pM LTX for 6.5 or 13 min resulted in the nearly complete restoration of uncleaved SNAP-25 within 48 h, whereas treatment with 60 mM K⁺ had no effect. Time-lapse imaging demonstrated that LTX treatment caused a profound increase in Ca²⁺ influx and evidence of excitotoxicity, though ESNs remained viable 48 h after LTX treatment. This is the first instance of a cell-based treatment that has shown the ability to eliminate BoNT activity. These data suggest that LTX treatment may provide the basis for a new class of therapeutic approach to BoNT intoxication and may contribute to an improved understanding of long-term mechanisms of BoNT intoxication and recovery. They further demonstrate that ESNs are a novel, responsive and biologically relevant model for LTX research and BoNT therapeutic drug discovery.

Novel venom gene discovery in the platypus

BACKGROUND

To date, few peptides in the complex mixture of platypus venom have been identified and sequenced, in part due to the limited amounts of platypus venom available to study. We have constructed and sequenced a cDNA library from an active platypus venom gland to identify the remaining components.

RESULTS

We identified 83 novel putative platypus venom genes from 13 toxin families, which are homologous to known toxins from a wide range of vertebrates (fish, reptiles, insectivores) and invertebrates (spiders, sea anemones, starfish). A number of these are expressed in tissues other than the venom gland, and at least three of these families (those with homology to toxins from distant invertebrates) may play non-toxin roles. Thus, further functional testing is required to confirm venom activity. However, the presence of similar putative toxins in such widely divergent species provides further evidence for the hypothesis that there are certain protein families that are selected preferentially during evolution to become venom peptides. We have also used homology with known proteins to speculate on the contributions of each venom component to the symptoms of platypus envenomation.

CONCLUSIONS

This study represents a step towards fully characterizing the first mammal venom transcriptome. We have found similarities between putative platypus toxins and those of a number of unrelated species, providing insight into the evolution of mammalian venom.