Identification of α - Syntrophin Binding to Syntrophin Triplet , Dystrophin , and Utrophin

Syntrophin represents three cytoplasmic components of the dystrophin-glycoprotein complex that links the cytoskeleton to the extracellular matrix in skeletal muscle. α-Syntrophin has now been translated in vitro and shown to associate directly with all three components of the syntrophin triplet and with dystrophin. The in vitro translated 71-kDa non-muscle dystrophin isoform, containing the cysteine-rich/C-terminal domain, can also interact with the syntrophin triplet. The syntrophin binding motif in dystrophin was localized to exons 73 and 74 including amino acids 3447-3481 by comparing the interactions of α-syntrophin and seven overlapping human dystrophin fusion proteins. More than one syntrophin interaction site in this binding motif was suggested. α-Syntrophin also interacts directly with a Ctenninal utrophin fusion protein. α-Syntrophin is localized to the muscle sarcolemma as well as to the neuromuscular junction in control mouse muscle. However, similar to utrophin, α-syntrophin is only present at the neuromuscular junction in mdx mouse muscle in which dystrophin is absent. Our data suggest that α-syntrophin binds all syntrophin isoforms, and syntrophin directly interacts with dystrophin through more than one binding site in dystrophin exons 73 and 74 including amino acids 3447-3481.