Neuronal cell surface protein that may be involved in cell recognition and cell adhesion. The cytoplasmic C-terminal region binds to CASK. Specific isoforms bind alpha-dystroglycan and neuroligins NLGN1, NLGN2 and NLGN3 (By similarity). Interacts with CBLN1, CBLN2 and, less avidly, with CBLN4 (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. Additional isoforms produced by alternative splicing seem to exist. Alternative splicing in the laminin G-like domain regulates binding to alpha-dystroglycan. Belongs to the neurexin family.