Latrotoxin

A latrotoxin is a high-molecular mass neurotoxin found in the venom of spiders of the genus Latrodectus (widow spiders). Latrotoxin are the main active components of the venom and are responsible for the symptoms of latrodectism.

The following latrotoxins have been described: five insecticidal toxins, termed α, β, γ, δ and ε-latroinsectotoxins, one vertebrate-specific neurotoxin, alpha-latrotoxin, and one toxin affecting crustaceans, α-latrocrustatoxin.

α-Latrotoxin

The best-studied latrotoxin is alpha-latrotoxin, which acts presynaptically to release neurotransmitters (including acetylcholine) from sensory and motor neurons, as well as on endocrine cells (to release insulin, for example). It is a ~130 kDa protein which exists mainly in its dimerized or tetramerized forms.

Latroinsectotoxins

The natural prey of widow spiders are insects, and several insectotoxins are found in its venom. The latroinsectotoxins appear to have similar structures.

Other venom components

Apart from the high molecular weight latrotoxins described above, Latrodectus venom also contains low molecular weight proteins whose function has not been explored fully yet, but may be involved in facilitating membrane insertion of latrotoxins.^{[citation needed]}