Glycoprotein Complex Anchoring Dystrophin to Sarcolemma

Abstract

We found six groups of proteins, A0-A5, besides dystrophin itself in a dystrophin preparation obtained by the reported method [Campbell, K. P. & Kahl, S. D. (1989) Nature 338, 259-262] with some modifications. Their molecular weights were 94, 62, 52, 43, 36, and 24 kDa, respectively. Their molar ratios to dystrophin were 0.14, 2.2, 0.88, 0.90, 1.7, and 0.34, respectively. Each of Al, A3, and A4 was split into several bands. But each group of bands except A3 seemed to behave like the same kind of protein. The doublet of A3 was subdivided into A3a and A3b in the decreasing order of molecular weight. All the A-proteins except A2 were cross-linked with dystrophin molecule by a cross-linker, bis(sulfosuccinimidyl)suberate, suggesting them to be dystrophin-associated proteins. When dystrophin preparation was treated with KI, which is known to break membrane cytoskeletal interactions, as described by Campbell and Kahl, A2, A3, and A4 were absorbed by wheat germ lectin (WGL) Sepharose, but the dystrophin molecule and Al were not absorbed. On the other hand, A2 and A3b reacted with biotinyl WGL but A3a and A4 did not in blotting analysis. This apparent discrepancy can be explained if we postulate that A3a and/or A4 would associate with A2 and/or A3b. On the basis of these results including stoichiometric considerations, we are of the opinion that the complex of A2. A4 among various possible ones is the most important to anchor dystrophin to sarcolemma. In this A2-A4 complex, A4 but not A2 is directly associated with dystrophin.