A role for the dystrophin-glycoprotein complex as a transmembrane linker between laminin and actin.
The dystrophin-glycoprotein complex was tested for interaction with several components of the extracellular matrix as well as actin. The 156-kD dystrophin-associated glycoprotein (156-kD dystroglycan) specifically bound laminin in a calcium-dependent manner and was inhibited by NaCl (IC50 = 250 mM) but was not affected by 1,000-fold (wt/wt) excesses of lactose, IKVAV, or YIGSR peptides. Laminin binding was inhibited by heparin (IC50 = 100 micrograms/ml), suggesting that one of the heparin-binding domains of laminin is involved in binding dystroglycan while negatively charged oligosaccharide moieties on dystroglycan were found to be necessary for its laminin-binding activity. No interaction between any component of the dystrophin-glycoprotein complex and fibronectin, collagen I, collagen IV, entactin, or heparan sulfate proteoglycan was detected by 125I-protein overlay and/or extracellular matrix protein-Sepharose precipitation. In addition, laminin-Sepharose quantitatively precipitated purified dystrophin-glycoprotein complex, demonstrating that the laminin-binding site is accessible when dystroglycan is associated with the complex. Dystroglycan of nonmuscle tissues also bound laminin. However, the other proteins of the striated muscle dystrophin-glycoprotein complex appear to be absent, antigenically dissimilar or less tightly associated with dystroglycan in nonmuscle tissues. Finally, we show that the dystrophin-glycoprotein complex cosediments with F-actin but does not bind calcium or calmodulin. Our results support a role for the striated muscle dystrophin-glycoprotein complex in linking the actin-based cytoskeleton with the extracellular matrix. Furthermore, our results suggest that dystrophin and dystroglycan may play substantially different functional roles in nonmuscle tissues.
Ervasti
J M
JM
Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City 52242.
Campbell
K P
KP
D000199:Actins / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003599:Cytoskeleton / Q000648:ultrastructure; D049030:Dystroglycans; D016189:Dystrophin / Q000502:physiology*; D005109:Extracellular Matrix / Q000378:metabolism; D006023:Glycoproteins / Q000502:physiology*; D006493:Heparin / Q000378:metabolism; D007797:Laminin / Q000502:physiology*; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D012508:Sarcolemma / Q000648:ultrastructure*
D000199:Actins; D000911:Antibodies, Monoclonal; D002147:Calmodulin; D003598:Cytoskeletal Proteins; D016189:Dystrophin; D006023:Glycoproteins; D007797:Laminin; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D010455:Peptides; D049030:Dystroglycans; D006493:Heparin; D002118:Calcium