High affinity binding of alpha-latrotoxin to recombinant neurexin I alpha.

alpha-Latrotoxin is a potent neurotoxin from black widow spider venom that stimulates neurotransmitter release. alpha-Latrotoxin is thought to act by binding to a high affinity receptor on presynaptic nerve terminals. In previous studies, high affinity alpha-latrotoxin binding proteins were isolated and demonstrated to contain neurexin I alpha as a major component. Neurexin I alpha is a cell surface protein that exists in multiple differentially spliced isoforms and belongs to a large family of neuron-specific proteins. Using a series of neurexin I-IgG fusion proteins, we now show that recombinant neurexin I alpha binds alpha-latrotoxin directly with high affinity (Kd approximately 4 nM). Binding of alpha-latrotoxin to recombinant neurexin I alpha is dependent on Ca2+ (EC50 approximately 30 microM). Our data suggest that neurexin I alpha is a Ca(2+)-dependent high affinity receptor for alpha-latrotoxin.