Determination and regulation of half-life of the proteins

目前，钙激活中性蛋白酶（calpain）家族成员在下调关键信号分子和哺乳动物细胞内蛋白降解中发挥着关键的生物学作用。在鸡中，我们通过cDNA克隆、杆状病毒表达和酶纯化，鉴定出m-、m/m-和m-calpain三种常规亚型。我们推测，这些酶都是作为一个无活性的前酶（80 kDa加30 kDa）合成的，该酶被蛋白水解激活形成一个80 kDa的单体催化酶。遗传性四肢带状肌营养不良2A型（LGMD2A）是一种罕见的以肌肉萎缩为特征的遗传性疾病。据报道，肌肉特异性钙蛋白酶p94基因的几个缺失突变与LGMD2A表型相关。我们发现p94附着在肌肉弹性蛋白连接蛋白上，p94基因的突变破坏了酶与连接蛋白的联系。在这些LGMD2A患者中，p94自溶活性的丧失会抑制自身消化和肌肉结构的分离，从而导致肌肉萎缩。

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.