Dystrophin: Proteins and Enzymes

Dystrophin is a muscle membrane protein (427 kDa) which is absent, reduced or altered as a result of mutation in Duchenne and Becker muscular dystrophies (DMD/BMD) or its homologue in the mouse.8 Severe DMD is associated with a marked dystrophin deficiency whereas patients with the milder form of BMD show less pronounced abnormalities of protein expression. Because abnormalities in the protein expression occur specifically in patients with these types of muscular dystrophy, dystrophin analysis may be used to distinguish these conditions from other neuromuscular diseases. Predictions from the sequence suggest a structural protein on the inner face of the membrane, consisting of a 25-repeat, rod-like triple-helical domain separating an N-terminal actin-binding domain from two C-terminal domains, one of which is rich in cysteine.9 The large size of dystrophin and its low abundance (<0.01% of the total muscle protein) are a hindrance to the isolation of intact, native protein for structure/function studies. Monoclonal antibodies against defined regions10 of dystrophin provide a means for studying its structure and function, interactions with other proteins and the nature of the partial gene products produced in some patients carrying deletions in the dystrophin gene. The antibodies are useful in the prenatal or post-abortion diagnosis of muscular dystrophy carriers by immunohistological analyses.11