High Affinity Binding of α-Latrotoxin to Recombinant Neurexin Iα(∗)

α-Latrotoxin is a potent neurotoxin from black widow spider venom that stimulates neurotransmitter release. α-Latrotoxin is thought to act by binding to a high affinity receptor on presynaptic nerve terminals. In previous studies, high affinity α-latrotoxin binding proteins were isolated and demonstrated to contain neurexin Iα as a major component. Neurexin Iα 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 Iα binds α-latrotoxin directly with high affinity (Kd≈ 4 nM). Binding of α-latrotoxin to recombinant neurexin Iα is dependent on Ca2+ (EC50≈ 30 μM). Our data suggest that neurexin Iα is a Ca2+-dependent high affinity receptor for α-latrotoxin.