Center for Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.
PLoS One. 2010 Aug 4;5(8):e11940. doi: 10.1371/journal.pone.0011940.
Calpain 3 (CAPN3) is a cysteine protease that when mutated causes Limb Girdle Muscular Dystrophy 2A. It is thereby the only described Calpain family member that genetically causes a disease. Due to its inherent instability little is known of its substrates or its mechanism of activity and pathogenicity. In this investigation we define a primary sequence motif underlying CAPN3 substrate cleavage. This motif can transform non-related proteins into substrates, and identifies >300 new putative CAPN3 targets. Bioinformatic analyses of these targets demonstrate a critical role in muscle cytoskeletal remodeling and identify novel CAPN3 functions. Among the new CAPN3 substrates are three E3 SUMO ligases of the Protein Inhibitor of Activated Stats (PIAS) family. CAPN3 can cleave PIAS proteins and negatively regulates PIAS3 sumoylase activity. Consequently, SUMO2 is deregulated in patient muscle tissue. Our study thus uncovers unexpected crosstalk between CAPN3 proteolysis and protein sumoylation, with strong implications for muscle remodeling.
钙蛋白酶 3（CAPN3）是一种半胱氨酸蛋白酶，当其发生突变时会导致 2A 型肢带型肌营养不良症。因此，它是唯一一种已知可通过遗传导致疾病的钙蛋白酶家族成员。由于其内在的不稳定性，人们对其底物或其活性和致病性的机制知之甚少。在这项研究中，我们定义了一个CAPN3 底物切割的基本序列基序。该基序可以将非相关蛋白转化为底物，并鉴定出 >300 个新的潜在 CAPN3 靶标。对这些靶标的生物信息学分析表明，它们在肌肉细胞骨架重塑中起着关键作用，并确定了 CAPN3 的新功能。在新的 CAPN3 底物中，有三种蛋白抑制剂 of Activated Stats（PIAS）家族的 E3 SUMO 连接酶。CAPN3 可以切割 PIAS 蛋白，并负调控 PIAS3 连接酶的活性。因此，SUMO2 在患者的肌肉组织中失调。我们的研究揭示了 CAPN3 蛋白水解和蛋白 SUMO 化之间意想不到的串扰，这对肌肉重塑具有重要意义。
