Dystroglycans are essential elements of the neuromuscular junction (NMJ). The gene for dystroglycan is expressed as a precursor protein that is post-translationally cleaved into a 156 kDa extracellular peripheral membrane protein called alpha-dystroglycan and a 43 kDa transmembrane protein, beta-Dystroglycan. The latter protein contains a PPxY motif that promotes binding to WW domain-containing proteins, such as utrophin and dystrophin. Phosphorylation at tyrosine 892 within the PPxY motif may regulate c-Src interactions with beta-Dystroglycan, as well as inhibit interactions with WW domain proteins. In skeletal muscle, beta-Dystroglycan is normally localized to the plasma membrane, however phosphorylation of Tyr-892 leads to localization of beta-Dystroglycan to endosomal compartments along with c-Src. Thus, phosphorylation at Tyr-892 may have important roles in altering the localization of beta-Dystroglycan during NMJ formation.
