Cell adhesion, ankyrin-binding protein which may be involved in neurite extension, axonal guidance, synaptogenesis, myelination and neuron-glial cell interactions. Isoform 2/isoform 3 may be responsible for mediating and signaling axon-glial interaction during the early stages of myelination. Horseshoe-shaped homodimer (By similarity). Probable constituent of a NFASC/NRCAM/ankyrin G complex. Associates with the sodium channel beta-1 (SCN1B) and beta-3 (SCN3B) subunits. Associates to subunit beta-1 in developing axons as early as postanatal day 5, during the period that nodes of Ranvier are forming. Isoform 2/isoform 3 is likely to interact with axonal proteins in close association with CNTNAP1. Interacts with GLDN/gliomedin. Interacts with MYOC (By similarity). Isoform 1 colocalizes with ankyrin G at the nodes of Ranvier. Isoform 2/ isoform 3 is a glial component of the paranodal axo-glial junction. Isoform 1 is expressed at Nodes of Ranvier while isoform 2/isoform 3 is expressed in unmyelinated axons. Strongly but transiently up-regulated in oligodendrocytes at the onset of myelinogenesis. Once these last have engaged their target exons, expression declines precipitously. Homophilic adhesion is primarily mediated by the interaction of the second Ig-like domains. Isoform 2/isoform 3 is phosphorylated at P12. Dephosphorylation is required for ankyrin binding. Belongs to the immunoglobulin superfamily. L1/neurofascin/NgCAM family.