Muscle-specific Calpain, p94, Responsible for Limb Girdle Muscular Dystrophy Type 2A, Associates with Connectin through IS2, a p94-specific Sequence

Abstract

p94, a muscle-specific member of calpain family, is unique in that it undergoes rapid and exhaustive autolysis with a half-life of less than 1 h resulting in its disappearance from muscle. Recently, p94 was shown to be responsible for limb girdle muscular dystrophy type 2A. To elucidate the muscular proteolytic system mediated by p94 and to solve the mystery of its unusually rapid autolysis, we searched for p94-binding proteins by the two-hybrid system. Although calpain small subunit plays a crucial role for regulation of ubiquitous calpains, it did not associate with p94. After a screening of skeletal muscle library, connectin (or titin), a gigantic filamentous protein spanning the M-to Z-lines of muscle sarcomere, was found to bind to p94 through a p94-specific region, IS2. The connectin-insoluble fraction of washed myofibrils contained full-length intact p94, suggesting that connectin regulates p94 activity.Proteolysis in cytosol is a key reaction to modulate various intracellular protein functions such as signal transduction, protein turnover, and cell structure. Calpain, Ca 2ϩ -dependent cysteine proteinase (EC 3.4.22.17), is one of the major intracellular proteinases known as interacting various protein kinases, transcription factors, and cytoskeletal proteins (1-5). Ubiquitous -and m-calpains, dimers of a large catalytic (CL 1 (6) and mCL (7), respectively) and small regulatory (30K (8)) subunit. Recently, we found that the ubiquitous calpain large subunit monomer can express full proteolytic activity, and that 30K dissociates from the large subunit upon activation by Ca 2ϩ (9, 10). In other words, 30K together with calpastatin, a specific proteinaceous inhibitor for calpain, play pivotal roles in regulation of calpain activity.p94 is a muscle-specific member of the calpain large subunit family, and distinct not only from the other members but also from other proteases in that it autolyzes very rapidly and extensively leading to almost complete disappearance right after translation even in the presence of EGTA and leupeptin as observed in vitro (11,12). Ubiquitous calpains as well as many other proteases also undergo autolysis at the NH 2 terminus, but only to a limited extent. Quite recently, p94 was identified as responsible for limb girdle muscular dystrophy type 2A (LGMD2A), the first demonstration of the involvement of an enzyme in muscle dystrophy (13). To elucidate physiological meaning of this exhaustive autolysis and the molecular mechanism connecting LGMD2A and p94 function, it is important to clarify the substrates of p94 and the manner to regulate the proteolytic activity of p94.30K is the first candidate to bind to and regulate p94, since the calmodulin-like Ca 2ϩ -binding domains of CL and mCL (see Fig. 2), which are the binding sites for 30K, are highly homologous to p94 (5). Analysis of p94 at the protein level, however, is very difficult because of the extremely rapid autolysis, and, thus, we examined using the yeast two-hybrid system (14). As a result, 30K was revealed not to bind to p94...

Anthracyclines Induce Calpain-dependent Titin Proteolysis and Necrosis in Cardiomyocytes

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Characterization and Regulation of Lens-specific Calpain Lp82

“…We found that the longer N-terminal extension on domain I of Lp82 could interfere with the association of Lp82 with calpain 4. This was similar to the predicted lack of association between calpain 4 and calpain 3 (16), possibly because of long domain I (Fig. 6B).…”

Muscle type-specific responses of myoD and calpain 3 expression to recombinant porcine growth hormone in the pig

“…Mutations in the calpain 3 have been shown to be responsible for limb-girdle muscular dystrophy type 2A (Sorimachi et al, 1995). Jones et al (1999) demonstrated that calpain 3 was present in all fibres of pigs but at a significantly lower level in slow type I compared with fast type IIA/IIB fibres, as observed in the present study.…”