Secretory Pathways in Neurons 
cifically to the presynaptic membrane and causes 
massive neurotransmitter release. Purification 
and amino acid sequencing of the receptor for 
a-latrotoxin led to the discovery of a new family 
of neuron-specific cell surface proteins that we 
named neurexins. Their structure and localiza- 
tion suggest that they may be synaptic recogni- 
tion molecules. 
Surprisingly, we also found that the a-latrotoxin 
receptor interacts with a synaptic vesicle protein, 
synaptotagmin, whose Ca -binding properties 
have already implicated it in exocytosis. These 
results raise the possibility that the neurexins 
may have a role in aligning the synapse both 
extra- and intracellularly. Further studies of the 
neurexins should allow us to gain new insights 
into how synapses are formed and neurotransmit- 
ters released. Results should be relevant for un- 
derstanding brain function under normal and 
pathologic conditions. 
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