Proteomics of the dystrophin-glycoprotein complex and dystrophinopathy.

The largest human gene is represented by the X-chromosomal dystrophin gene of 2.4 million bases, which encodes for the membrane cytoskeletal protein dystrophin. The dystrophin isoform Dp427 has a subsarcolemmal location and forms a supramolecular membrane assembly with a variety of glycoproteins. In healthy muscle fibres, dystrophin acts as an actin-binding protein that links the cytoskeleton via the α/β-dystroglycan complex to the extracellular matrix protein laminin. This trans-sarcolemmal complex is believed to stabilize the muscle surface and thus prevents membrane rupturing during excitation-contraction-relaxation cycles. In the highly progressive muscle wasting disease Duchenne muscular dystrophy, the primary deficiency in dystrophin causes a drastic reduction in dystrophin-associated glycoproteins, which renders muscle fibres more susceptible to necrosis. Following the biochemical and cell biological characterization of the dystrophin-glycoprotein complex, several mass spectrometry-based proteomic studies have investigated global changes in dystrophin-deficient muscle tissues. This review briefly outlines the basic domain structure of Dp427 and the composition of the dystrophin-associated glycoprotein complex from skeletal muscle. A detailed discussion of recent proteomic analyses of the purified dystrophin-glycoprotein complex is included, as well as a summary of mass spectrometric surveys of dystrophic specimens. The study of these new areas of muscle proteomics tends to improve our understanding of the normal function of dystrophin in contractile fibres and better define the molecular mechanism of X-linked muscular dystrophy.