Latrotoxins (LaTXs) are presynaptic pore-forming neurotoxins found in the venom of black widow spiders. The venom contains a toxic cocktail of seven LaTXs, with one of them targeting vertebrates (α-latrotoxin (α-LTX)), five specialized on insects (α, β, γ, δ, ε- latroinsectotoxins (LITs), and one on crustaceans (α-latrocrustatoxin (α-LCT)). The vertebrate specific αLTX specifically targets the molecular machinery of exocytosis. Upon binding to specific receptors on the surface of neuronal cells, LTXs undergo a structural metamorphosis from a soluble, inactive monomer to an active tetramer that inserts into the presynaptic membrane, forming a cation-selective pore and inducing massive neurotransmitter release. This prominent natural toxin, is thus mimicking Ca2+ influx via voltage-gated Ca2+ channels during an action potential and its actions are considered precisely the opposite of those of botulinum and tetanus toxins. A structural and mechanistic understanding of LTX function is a significant priority for the development of novel therapeutics, treatment of botulism and neuromuscular paralysis and/or development of tailored bio-insecticides.
My talk will focus on the mechanism of LTX pore formation. Using advanced cryoEM single particle analysis, complemented by extensive MD simulations, electrophysiological studies, AlphaFold2 predictions and reconstitution experiments in liposomes, we elucidated the key steps of a-LTX action at the presynaptic membrane. Our studies reveal a unique and intriguing mechanism for membrane insertion and channel formation characteristic of the LTX family and allow us to explain in unprecedented detail the biochemical and functional data accumulated over the last decades. In addition, the comparative structural analysis between the different members of the LTX family provides the first crucial molecular insights into LTX phylum-specificity and, together, the necessary framework for advancing novel therapeutics and biotechnological applications.