Neuronal cell surface protein that may be involved in cell recognition and cell adhesion. May play a role in angiogenesis (By similarity). Weakly interacts with CBLN1 and CBLN2 (By similarity). Very weak binding, if any, with CBLN4 (By similarity). Additional isoforms seem to exist. There is a combination of two alternatively spliced domains at sites 4 and 5, which seem to be used independently. Experimental confirmation may be lacking for some isoforms. Proccessed by alpha-secretase leading to the formation of an extracellular soluble protein as well as a C-terminal membrane-embedded fragment (CTF). Proteolysis of these CTFs by gamma-secretase releases intracellular domains (ICDs) and extracellular peptides (By similarity). Lacks the transmembrane domain. Lacks the transmembrane domain. Belongs to the neurexin family.