A DYSTROPHIN-ASSOCIATED GLYCOPROTEIN, A3A (ONE OF 43DAG DOUBLETS), ISRETAINED IN DUCHENNE MUSCULAR-DYSTROPHY MUSCLE

We determined several internal amino acid sequences of dystrophin-asso ciated glycoprotein, A3a (one of the 43DAG doublets), of rabbit skelet al muscle. All the sequences of A3a determined were found in the C-ter minal region of dystroglycan, which is the region assumed to be the cy toplasmic domain of 43DAG; [Ibraghimov-Beskrovnaya et al. (1992) Natur e 355, 696-702]. Therefore, A3a is identical with 43DAG. We raised an antibody (PA3a) against a synthetic polypeptide equivalent to one of t he internal amino acid sequences of A3a. The antibody specifically rea cted with A3a of rabbit skeletal muscle. PA3a, however, did not react with A3b, the other 43DAG doublet, suggesting that the 43DAG doublets are different proteins from each other. When the human control muscles were examined, PA3a immunohistochemically stained the cell surface me mbranes and exclusively reacted with a single protein similar to A3a i n the SDS extracts. The protein was also detected in the SDS extract o f the Duchenne muscular dystrophy (DMD) muscle devoid of dystrophin. W hen the muscle specimens from 30 DMD patients were immunohistochemical ly examined with the antibody, the cell surface membranes were consist ently stained. Therefore, we conclude that the dystrophin-associated p rotein, A3a, is retained in DMD muscles.