Adapter protein that binds to and probably organizes the subcellular localization of a variety of membrane proteins. May link various receptors to the actin cytoskeleton and the extracellular matrix via the dystrophin glycoprotein complex. Plays an important role in synapse formation and in the organization of UTRN and acetylcholine receptors at the neuromuscular synapse. Binds to phosphatidylinositol 4,5-bisphosphate. Monomer and homodimer. Interacts with MAPK12, TGFA, GA and F-actin (By similarity). Interacts with the other members of the syntrophin family: SNTB1 and SNTB2; with dystrophin protein DMD and related proteins DTNA and UTRN; SGCG and SGCA of the dystrophin glycoprotein complex; NOS1; GRB2; calmodulin and the sodium channel proteins SCN4A and SCN5A. Interacts with MYOC; regulates muscle hypertrophy. Interacts with DTNB (PubMed:10893187). In skeletal muscle, it localizes at the cytoplasmic side of the sarcolemmal membrane and at neuromuscular junctions. High expression in skeletal muscle. Expressed at intermediate level in heart, kidney and brain, and at low level in intestine, liver, lung and testis. The PH 1 domain mediates the oligomerization in a calcium dependent manner, and the association with the phosphatidylinositol 4,5-bisphosphate. The PDZ domain binds to the last three or four amino acids of ion channels and receptor proteins. The association with dystrophin or related proteins probably leaves the PDZ domain available to recruit proteins to the membrane. The SU domain binds calmodulin in a calcium-dependent manner. Phosphorylated by CaM-kinase II. Phosphorylation may inhibit the interaction with DMD. Belongs to the syntrophin family.