Determination and regulation of half-life of the proteins

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It is now clear that member of the calpain (calcium-activated neutral protease) family play key biological roles in down-regulation of key signal molecules and mammalian intracellular protein degradation. In chicken, we identified three conventional isoforms, m-, m/m- and m-calpains, according to cDNA cloning followed by expression in baculovirus and purification of the enzymes. We speculate that each of these enzymes is synthesized as an inactive proenzyme (80 kDa plus 30 kDa) that is proteolytically activated to form an 80 kDa monomeric catalytic enzyme.Hereditary Limb-Girdle muscular dystrophy type 2A (LGMD2A) is a rare genetic disorder characterized by muscle atrophy. Several missence mutations of the muscle specific calpain, p94, gene have been reported to be associated with the LGMD2A phenotype. We found that p94 is attached to muscle elastic protein connectin and the mutation of the p94 gene disrupted the association of the enzyme with connectin. Loss of autolytic activity of p94 in these LGMD2A patients would permit both inhibition of autodigestion and dissociation from muscle structure resulting in muscle atrophy.