Selective presynaptic insectotoxin (α-latroinsectotoxin) isolated from black widow spider venom

Abstract

A homogenous protein of 120,000 mol. wt isolated from black widow spider ( Lactrodectus mactans tredecimguttatus) venom and referred to as α-latroinsectotoxin was highly potent (4nM) in the induction of an increase of the frequency of miniature excitatory postsynaptic potentials in blowfly ( Calliphora vicina) larvae neuromuscular preparations. In the frog nerve ending, however, even 50 nM α-latroinsectotoxin failed to affect transmitter release. Pretreatment of insect preparations with α-latrotoxin or frog preparations with α-latroinsectotoxin did not prevent the specific effect of consequent applications of α-latroinsectotoxin (insect) and α-latrotoxin (frog), respectively. The binding of labelled [ 125I]α-latroinsectotoxin to insect and [ 125I]α-latrotoxin to bovine membrane preparations was saturable and highly specific. The presynaptic effect, but not the binding of α-latroinsectotoxin, was dependent on the presence of divalent cations in the external medium. Mg 2+ could readily substitute for Ca 2+ and increase of transmitter release induced by α-latroinsectotoxin also occurred in Ca 2+-free solutions. Pretreatment of preparations with 300μg/ml concanavalin A completely abolished both the presynaptic effect of α-latroinsectotoxin and its binding to insect membrane preparations. Thus, the phenomenology of α-latroinsectotoxin action on insects resembles in general that described for the action of α-latrotoxin on vertebrates. The selectivity of α-latrotoxin and α-latroinsectotoxin seems to be due to differences in the structure of neurotoxin receptors in nerve endings of vertebrates and insects, although the mode of presynaptic action has a great deal in common.