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. May play a role in the regulation of secretory granules via its interaction with PTPRN. Monomer and homodimer (Probable). Interacts with the other members of the syntrophin family: SNTA1 and SNTB1; and with the sodium channel proteins SCN4A and SCN5A. Interacts with SAST, MAST205, microtubules and microtubule-associated proteins (By similarity). Interacts with the dystrophin protein DMD and related proteins DTNA and UTRN, and with the neuroregulin receptor ERBB4. Interacts with PTPRN when phosphorylated, protecting PTPRN from protein cleavage by CAPN1. Dephosphorylation upon insulin stimulation disrupts the interaction with PTPRN and results in the cleavage of PTPRN. Interacts with DTNB (By similarity). Membrane-associated. In muscle, it is exclusively localized at the neuromuscular junction (By similarity). In insulinoma cell line, it is enriched in secretory granules. Ubiquitous. Isoform 1 is the predominant isoform. Weak level of isoform 2 is present in all tested tissues, except in liver and heart where it is highly expressed. 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. Partially dephosphorylated upon insulin stimulation. Lacks domains required for interaction with dystrophin related proteins. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the syntrophin family.