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 with CBLN2 and more weakly with CBLN4 (PubMed:22220752, PubMed:29782851). Interacts with CBLN1; interaction is CBLN1 hexamer form-dependent; CBLN1-binding is calcium-independent; isoform 1b does not interact with CBLN1 (PubMed:21410790, PubMed:22220752, PubMed:29782851). 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. Highly O-glycosylated and minor N-glycosylated. Belongs to the neurexin family.