alpha-latrotoxin triggers transmitter release via direct insertion into the presynaptic plasma membrane

Abstract

α-latrotoxin, a component of black widow spider venom, binds to presynaptic nerve terminals and stimulates massive neurotransmitter release. Previous studies have demonstrated that α-latrotoxin first binds to two high-affinity receptors on nerve terminals, neurexins and CLs (CIRLs and latrophilins), and then executes a critical, second step,of unknown nature that stimulates neurotransmitter release. We now demonstrate that incubation of α-latrotoxin with synaptosomes at 0°C results in its peripheral membrane association. Incubation at 37°C, however, converts the toxin into an operationally integral membrane protein, and induces generation of a protease-resistant fragment that consists of: the entire N-terminal domain of α-latrotoxin and becomes protease sensitive after lysis of synaptosomes. Our data suggest that α-latrotoxin inserts into the presynaptic plasma membrane after receptor binding, resulting in an intracellular location of the N-terminal sequences. Membrane insertion of the N-terminal domain of α-latrotoxin occurs spontaneously, independently of membrane recycling or transmembrane ion gradients. We postulate that α-latrotoxin acts intracellularly in triggering release, and propose that non-selective cation channels induced by α-latrotoxin may be a by-product of membrane insertion.