Neuronal cell surface protein that may be involved in cell recognition and cell adhesion. May mediate intracellular signaling. The laminin G-like domain 1 binds to NXPH1 (PubMed:9856994). Interacts with PATJ (PubMed:9647694). Interacts with CBLN1, CBLN2 and, less avidly, with CBLN4 (By similarity). Isoforms alpha 2C bind to alpha-dystroglycan (PubMed:11470830). Interacts (via Laminin G-like 1 domain) with IGSF21 (Ig-like 1 domain) in a trans-interaction manner (By similarity). Two isoform types, alpha-type and beta-type are produced by alternative promoter usage. In addition there are at least five major alternatively spliced sites, each of which may be spliced in up to three different ways. Additional isoforms may derive from a minor cytoplasmic splice site 6. Combinatorial splicing at each of these six sites may lead to the generation of at least 216 isoforms but for simplicity only individual splice events are explicitly described below. Beta-type isoforms share the possibility of alternative splicing at sites 4, 5 and 6. Experimental confirmation may be lacking for some isoforms. Brain (neuronal synapse). Belongs to the neurexin family.