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 (By similarity). Monomer and homodimer. Interacts with the dystrophin related protein DTNA; SGCG of the dystrophin glycoprotein complex; NOS1; GRB2; GA; TGFA; MAPK12 and the sodium channel proteins SCN4A and SCN5A. Interacts with the dystrophin protein DMD in a calmodulin dependent manner and with related protein UTRN; SGCA of the dystrophin glycoprotein complex; F-actin; calmodulin and with the other members of the syntrophin family SNTB1 and SNTB2. Interacts with MYOC; regulates muscle hypertrophy (By similarity). Interacts with DTNB (By similarity). In skeletal muscle, it localizes at the cytoplasmic side of the sarcolemmal membrane and at neuromuscular junctions. 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 (By similarity). The SU domain binds calmodulin in a calcium-dependent manner (By similarity). It contains actin-binding sites. Phosphorylated by CaM-kinase II. Phosphorylation may inhibit the interaction with DMD (By similarity). Belongs to the syntrophin family.