Cf. Ratcliffe et al., Sodium channel beta 1 and beta 3 subunits associate with neurofascin through their extracellular immunoglobulin-like domain, J CELL BIOL, 154(2), 2001, pp. 427-434
Sequence homology predicts that the extracellular domain of the sodium chan
nel beta1 subunit forms an immunoglobulin (Ig) fold and functions as a cell
adhesion molecule. We show here that beta1 subunits associate with neurofa
scin, a neuronal cell adhesion molecule that plays a key role in the assemb
ly of nodes of Ranvier. The first Ig-like domain and second fibronectin typ
e III-like domain of neurofascin mediate the interaction with the extracell
ular Ig-like domain of beta1, confirming the proposed function of this doma
in as a cell adhesion molecule. beta1 subunits localize to nodes of Ranvier
with neurofascin in sciatic nerve axons, and beta1 and neurofascin are ass
ociated as early as postnatal day 5, during the period that nodes of Ranvie
r are forming. This association of beta1 subunit extracellular domains with
neurofascin in developing axons may facilitate recruitment and concentrati
on of sodium channel complexes at nodes of Ranvier.