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 dystrophin glycoprotein complex. Monomer and homodimer (Probable). Interacts with the other members of the syntrophin family SNTA1 and SNTB2; with the sodium channel proteins SCN4A and SCN5A (By similarity). Interacts with the viral HTLV-1 TAX protein and with dystrophin protein DMD and related proteins DTNA and UTRN. Interacts with DTNB (By similarity). In skeletal muscle, it localizes at the cytoplasmic side of the sarcolemmal membrane and at neuromuscular junctions. Ubiquitous. The PH 1 domain mediates the oligomerization in a calcium dependent manner. 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. Phosphorylated by CaM-kinase II. Belongs to the syntrophin family.