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 A1, 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 A1 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.

Severe childhood autosomal recessive muscular dystrophy (SCARMD) is a progressive muscle-wasting disorder common in North Africa that segregates with microsatellite markers at chromosome 13q12. Here, it is shown that a mutation in the gene encoding the 35-kilodalton dystrophin-associated glycoprotein, gamma-sarcoglycan, is likely to be the primary genetic defect in this disorder. The human gamma-sarcoglycan gene was mapped to chromosome 13q12, and deletions that alter its reading frame were identified in three families and one of four sporadic cases of SCARMD. These mutations not only affect gamma-sarcoglycan but also disrupt the integrity of the entire sarcoglycan complex.

The dystrophin associated proteins (DAPs) are good candidates for harboring primary mutations in the genetically heterogeneous autosomal recessive muscular dystrophies (ARMD). The transmembrane components of the DAPs can be separated into the dystroglycan and the sarcoglycan complexes. Here we report the isolation of cDNAs encoding the 43 kD sarcoglycan protein beta-sarcoglycan (A3b) and the localization of the human gene to chromosome 4q12. We describe a young girl with ARMD with truncating mutations on both alleles. Immunostaining of her muscle biopsy shows specific loss of the components of the sarcoglycan complex (beta-sarcoglycan, alpha-sarcoglycan (adhalin), and 35 kD sarcoglycan). Thus secondary destabilization of the sarcoglycan complex may be an important pathophysiological event in ARMD.

The basal lamina of muscle fibers plays a crucial role in the development and function of skeletal muscle. An important laminin receptor in muscle is integrin alpha7beta1D. Integrin beta1 is expressed throughout the body, while integrin alpha7 is more muscle-specific. To address the role of integrin alpha7 in human muscle disease, we determined alpha7 protein expression in muscle biopsies from 117 patients with unclassified congenital myopathy and congenital muscular dystrophy by immunocytochemistry. We found three unrelated patients with integrin alpha7 deficiency and normal laminin alpha2 chain expression. To determine if any of these three patients had mutations of the integrin alpha7 gene, ITGA7, we cloned and sequenced the full-length human ITGA7 cDNA, and screened the patients for mutations. One patient had splice mutations on both alleles; one causing a 21-bp insertion in the conserved cysteine-rich region, and the other causing a 98-bp deletion. A second patient was a compound heterozygote for the same 98-bp deletion, and had a 1-bp frame-shift deletion on the other allele. A third showed marked deficiency of ITGA7 mRNA. Clinically, these patients showed congenital myopathy with delayed motor milestones. Our results demonstrate that mutations in ITGA7 are involved in a form of congenital myopathy.

Dystrophin is purified as a complex with several proteins from the digitonin-solubilized muscle cell membrane. Most of dystrophin-associated proteins (DAPs) are assumed to form a large oligomeric transmembranous glycoprotein complex on the sarcolemma and link dystrophin with a basement membrane protein, laminin. In the present study, we found that the purified dystrophin-DAP complex was dissociated into several groups by n-octyl-P-~-glucoside treatment. In particular, we found that the glycoprotein complex stated above was dissociated into two distinct groups: one composed of 156DAG and 43DAG (A3a) and the other composed of SODAG, 35DAG and A3b. We confirmed by crosslinking and immunoaffinity chromatography that these two groups existed in a complexes. We thus concluded that the glycoprotein complex consists of these two subcomplexes. Furthermore, A3b and 43DAG, which had been formerly treated simply as the 43DAG doublets due to their similar electrophoretic mobilities in SDS/PAGE, were shown to be present in two different subcomplexes. Based on the analyses by two-dimensional gel electrophoresis, peptide mapping and immunoblotting, we concluded that A3b is a novel DAP different from 43DAG. Dystrophin, the protein responsible for Duchenne muscular dystrophy [ l , 21, is purified as a complex with several proteins called dystrophin-associated proteins (DAPs) from digitonin-solubilized rabbit skeletal muscle membrane [3, 41. At least four DAPs, given the symbols 156DAG, SODAG, 43DAG doublets (A3a and A3b) and 35DAG, were shown to exist in the transmembranous glycoprotein complex (GPC) [5, 61. In the structural study of dystrophin or the complex of dystrophin and its associated proteins (dystrophin-DAP complex) by limited calpain digestion [7], we showed that the locus of GPC binding on the dystrophin molecule is confined to the cysteine-rich domain and the first half of the Cterminal domain [6]. Since this locus is known to be the region whose loss is responsible for Duchenne muscular dystrophy [8], this finding was the first experimental evidence showing that the interaction of GPC with dystrophin is essential to prevent muscle degeneration.Among the components of GPC, 156DAG [9, 101 and 43DAG [ l l ] were shown to bind directly to laminin and dystrophin, respectively. However, the molecular organization of GPC has not yet been clarified. Thus, its study is indispensable in order to clarify the molecular basis behind muscular dystrophy. We showed immunochemically that the components of GPC (50DAG and 35DAG) are expressed in striated muscles but not in smooth muscles such as uterus and aorta, whereas 43DAG is rather ubiquitously expressed in various tissues [12, 131. On the other hand, it was reported that in the muscles of patients with severe childhood autosoma1 recessive muscular dystrophy (SCARMD), 5ODAG is lost and 35DAG is reduced, while dystrophin and other DAPs are preserved [ 141. Similar observations were made in the skeletal muscle of dystrophic hamster [15, 161. We also observed that in the skeletal...