Required for gap junction formation (By similarity). Required, with CNTNAP1, for radial and longitudinal organization of myelinated axons. Plays a role in the formation of functional distinct domains critical for saltatory conduction of nerve impulses in myelinated nerve fibers. Demarcates the juxtaparanodal region of the axo-glial junction. Interacts (via C-terminus) with KCNA2. Expressed in the juxtaparadonal region. Belongs to the neurexin family.