The multiple actions of black widow spider toxins and their selective use in neurosecretion studies.

The black widow spider venom contains several large protein toxins--latrotoxins--that are selectively targeted against different classes of animals: vertebrates, insects, and crustaceans. These toxins are synthesised as large precursors that undergo proteolytic processing and activation in the lumen of the venom gland. The mature latrotoxins demonstrate strong functional structure conservation and contain multiple ankyrin repeats, which mediate toxin oligomerisation. The three-dimensional structure has been determined for alpha-latrotoxin (alphaLTX), a representative venom component toxic to vertebrates. This reconstruction explains the mechanism of alphaLTX pore formation by showing that it forms tetrameric complexes, harbouring a central channel, and that it is able to insert into lipid membranes. All latrotoxins cause massive release of neurotransmitters from nerve terminals of respective animals after binding to specific neuronal receptors. A G protein-coupled receptor latrophilin and a single-transmembrane receptor neurexin have been identified as major high-affinity receptors for alphaLTX. Latrotoxins act by several Ca(2+)-dependent and -independent mechanisms based on pore formation and activation of receptors. Mutant recombinant alphaLTX that does not form pores has been used to dissect the multiple actions of this toxin. As a result, important insights have been gained into the receptor signalling and the role of intracellular Ca(2+) stores in the effect of alphaLTX.