Cell surface protein involved in cell-cell-interactions, exocytosis of secretory granules and regulation of signal transmission. Function is isoform-specific. Alpha-type isoforms have a long N-terminus with six laminin G-like domains and play an important role in synaptic signal transmission. Alpha-type isoforms play a role in the regulation of calcium channel activity and Ca(2+)-triggered neurotransmitter release at synapses and at neuromuscular junctions. They play an important role in Ca(2+)-triggered exocytosis of secretory granules in pituitary gland. They may affect their functions at synapses and in endocrine cells via their interactions with proteins from the exocytotic machinery. Likewise, alpha-type isoforms play a role in regulating the activity of postsynaptic NMDA receptors, a subtype of glutamate-gated ion channels (By similarity). Both alpha-type and beta-type isoforms may play a role in the formation or maintenance of synaptic junctions via their interactions (via the extracellular domains) with neuroligin family members, CBLN1 or CBLN2. In vitro, triggers the de novo formation of presynaptic structures. May be involved in specification of excitatory synapses. Alpha-type isoforms were first identified as receptors for alpha-latrotoxin from spider venom. Interacts (via laminin G-like domain 2 and/or laminin G-like domain 6) with NLGN1 forming a heterotetramer, where one NLGN1 dimer interacts with one NRXN1 dimer (By similarity). Interacts (via cytoplasmic C-terminal region) with CASK (via the PDZ, SH3 and guanylate kinase-like domains) (PubMed:8786425, PubMed:12040031). Interacts (via cytoplasmic C-terminus) with CASKIN1 and APBA1 (PubMed:12040031). Interacts with SYT13 and SYTL1 (By similarity). Interacts (via laminin G-like domain 2 and/or laminin G-like domain 6) with NLGN1, NLGN2 and NLGN3; these interactions are calcium-dependent. Interacts with CBLN1, CBLN2 and, less avidly, with CBLN4 (By similarity). Interacts (via laminin G-like domain 2 and/or laminin G-like domain 6) with NLGN4. Interacts (via laminin G-like domain 2) with NXPH1 and NXPH3. Alpha-type isoforms (neurexin-1-alpha) interact (via laminin G-like domain 2 and/or laminin G-like domain 6) with DAG1 (via alpha-dystroglycan chain). Alpha-type isoforms interact with alpha-latrotoxin from spider venom. Isoform 9a and isoform 13a bind to DAG1 (via alpha-dystroglycan chain). Isoform 13a binds to alpha-latrotoxin. Interacts with LRRTM1, LRRTM2, LRRTM3 and LRRTM4. Two isoform types, alpha-type and beta-type are produced by alternative promoter usage. In addition there are at least five alternatively spliced sites, each of which may be spliced in up to seven different ways. Combinatorial splicing at each of these five sites may lead to the generation of at least 96 isoforms but for simplicity only individual splice events or observed combinations are explicitly described below. Beta-type isoforms share the possibility of alternative splicing at sites 4 and 5. Experimental confirmation may be lacking for some isoforms. Brain (neuronal synapse). N-glycosylated. O-glycosylated. Alpha-latrotoxin competes with alpha-dystroglycan for binding. Belongs to the neurexin family.