Neuronal cell surface protein that may be involved in cell recognition and cell adhesion by forming intracellular junctions through binding to neuroligins. May play a role in formation or maintenance of synaptic junctions. May mediate intracellular signaling. May play a role in angiogenesis (By similarity). The cytoplasmic C-terminal region binds to CASK. Binds NLGN1, NLGN2 and NLGN3, DAG1 (alpha-dystroglycan) and alpha-latrotoxin. Binding to neuroligins is calcium-dependent, and the binding preference ranks as follow: NLGN1 > NLGN4 >> NLGN3 > NLGN2 (By similarity). Interacts CBLN2 and more weakly with CBLN4 (By similarity). Interacts with CBLN1; interaction is CBLN1 hexamer form-dependent; CBLN1-binding is calcium-independent; isoform 1b does not interact with CBLN1 (By similarity). A number of isoforms alpha-type and beta-type are produced by alternative promoter usage. Beta-type isoforms differ from alpha-type isoforms in their N-terminus. 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 sites may lead to the generation of at least 96 isoforms. Experimental confirmation may be lacking for some isoforms. Highly O-glycosylated and minor N-glycosylated. Belongs to the neurexin family.