Membrane-cytoskeleton linker. May participate in the maintenance/targeting of ion channels and cell adhesion molecules at the nodes of Ranvier and axonal initial segments (By similarity). In skeletal muscle, required for costamere localization of DMD and betaDAG1. Regulates KCNA1 channel activity in function of dietary Mg(2+) levels, and thereby contributes to the regulation of renal Mg(2+) reabsorption (PubMed:23903368). May be a constituent of a NFASC/NRCAM/ankyrin G complex. Interacts with RHBG (By similarity). Directly interacts with DMD and betaDAG1; this interaction does not interfere with DMD-binding and is required for DMD and betaDAG1 retention at costameres. Interacts (via N-terminal ANK repeats) with SCHIP1 isoform 7 (via C-terminus); this interaction is required for the localization at axon initial segments (AISs) and nodes of Ranvier (NRs). Interacts with PLEC and FLNC (By similarity). Interacts with KCNA1; this inhibits channel activity (PubMed:23903368). Interacts with SCN5A (By similarity). In skeletal muscle, localized at costameres and neuromuscular junctions. In bone marrow-derived macrophages, isoforms 2 and 3 are associated with lysosomes. Expressed in many epithelial tissues, muscles and axons. Expressed in kidney, brain, skin, lung, liver, intestine, pancreas, heart and testis (at protein level). In testis, expressed in Leydig cells, but very weakly or not at all in Sertoli cells or seminiferous tubules. Expressed in macrophages (at protein level). In an in vitro model of myogenesis, not detected in proliferating myoblasts. Hardly detectable during the first days of differentiation. Expression greatly increases in mature myotubes. Up-regulated by high dietary Mg(2+) levels. Truncated N-terminus. Truncated N-terminus.