Toxin Name α-Latrotoxin-Lt1a
Source Species Latrodectus  tredecimguttatus (European black widow spider)
Toxin Group Theriditoxin
Description α-Latrotoxin-Lt1a is a presynaptic neurotoxin that causes massive neurotransmitter release from vertebrate (but not invertebrate) nerve terminals. It is synthesized as a 157-kDa precursor that is cleaved by furin-like proteases at both the N- and C-termini to produce an active mature toxin of ~131 kDa. An unusual feature of the primary structure is the presence of 22 ankyrin repeats. The toxin binds to neurexin Iα, latrophilin 1, and receptor-like protein tyrosine phosphatase σ, and is believed to induce neurotransmitter exocytosis through two calcium-dependent mechanisms (membrane pore formation and signalling via latrophilin) and a yet to be defined calcium-independent mechanism.

α-Latrotoxin-Lt1a appears to be the main neurotoxin responsible for the human envenomation syndrome known as latrodectism that results from bites by Latrodectus species. The venom can be lethal to humans as well as companion animals such as cats and dogs. Male spiders are up to 20 times smaller than females and are of little medical significance. Several antivenom preparations are available around the world but there is significant debate about their efficacy and the best route of administration (intravenous vs. intramuscular). However, current data support antivenom use in cases of latrodectism causing severe or persistent pain or systemic effects. Cross-reactivity of red-back spider antivenom (raised against the venom of L. hasselti) with many Latrodectus spp. and related Steatoda spp. suggests that homologs of α-latrotoxin-Lt1a may be present in other species.
Discovered 1990
Sex: Female, Prosoma length: 20mm
Photo courtesy of Bastian Rast
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This toxin last updated on Apr 06, 2011

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