Presynaptic neurotoxin that causes massive release of neurotransmitters from vertebrate (but not invertebrate) nerve terminals and endocrine cells via a complex mechanism involving activation of receptor(s) and toxin insertion into the plasma membrane with subsequent pore formation. Binds to neurexin-1-alpha (NRXN1) in a calcium dependent manner, adhesion G protein-coupled receptor L1 (ADGRL1, also termed latrophilin-1 and calcium-independent receptor of latrotoxin (CIRL)), and receptor-type tyrosine-protein phosphatase S (PTPRS), also termed PTP sigma. NRXN1 and PTPRS are suggested to provide a platform for binding and subsequent pore formation events. In contrast, binding to ADGRL1 does not involve oligomerization and channel formation, but direct downstream stimulation of the synaptic fusion machinery (By similarity). Induces rapid muscle contracture and loss of twitch tension when added to the isolated and indirectly stimulated chick biventer cervicis nerve-muscle preparation (PubMed:22001442). Homotetramer in membranes. Forms a membrane channel in the prey. Expressed in venom gland, cephalothorax, and abdomen tissues from both males and females. Expressed in all life stages examined, including adults, spiderlings and eggs. The H8 helix is predicted to insert into membranes and form pores by assembling into tetramers. The helix is contained within a helical bundle domain that undergoes significant conformational changes during pore formation to allow exposure of the H8 transmembrane helix and transition of the toxin from a soluble monomer to a transmembrane tetramer. Processed by furin-like proteases at both the N- and C-termini. LD(50)is 20 ug/kg by subcutaneous injection into mice. Is the main neurotoxin responsible for the human envenomation syndrome known as latrodectism that results from bites by Latrodectus species. Belongs to the cationic peptide 01 (latrotoxin) family. 03 (alpha-latrotoxin) subfamily.