OLIGOMERIZATION OF BETA-DYSTROGLYCAN IN RABBIT DIAPHRAGM AND BRAIN ASREVEALED BY CHEMICAL CROSS-LINKING

The surface component beta-dystroglycan is a member of the dystrophin- glycoprotein complex providing a trans-sarcolemmal linkage between the actin membrane cytoskeleton and the extracellular matrix component la minin-alpha 2. Although abnormalities in this complex are involved in the pathophysiology of various neuromuscular disorders, little is know n about the organization of dystrophin-associated glycoproteins in dia phragm and brain. We therefore investigated the oligomerization of bet a-dystroglycan and its connection with the most abundant dystrophin ho mologues in these two tissues. Employing detergent solubilization and alkaline extraction procedures of native membranes, it was confirmed t hat beta-dystroglycan behaves like an integral surface molecule as pre dicted by its cDNA sequence. Immunoblot analysis following chemical cr osslinking of native membranes showed that beta-dystroglycan has a ten dency to form high-molecular-mass complexes. Within these crosslinkabl e complexes, immune-reactive overlaps were observed between beta-dystr oglycan, alpha-dystroglycan, laminin and 427 kDa dystrophin in diaphra gm and skeletal muscle. In synaptosomes, the major brain dystrophin is oform Dp116 also exhibited an immune-reactive overlap with members of the dystroglycan complex. These findings demonstrate that beta-dystrog lycan does not exist as a monomer in native membranes and imply that c ertain dystrophin isoforms and dystrophin-associated components intera ct with this surface protein in diaphragm and brain as has been previo usly shown for skeletal and heart muscle. (C) 1998 Elsevier Science B. V.