Required for gap junction formation (Probable). 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. . This is the function of CNTNAP2 (contactin associated protein 2, ENSG00000174469).