Mishizen-Eberz Amanda J, Guttmann Rodney P, Giasson Benoit I, Day George A, Hodara Roberto, Ischiropoulos Harry, Lee Virginia M-Y, Trojanowski John Q, Lynch David R
Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
J Neurochem. 2003 Aug;86(4):836-47. doi: 10.1046/j.1471-4159.2003.01878.x.
Parkinson's disease (PD) is characterized by fibrillary neuronal inclusions called Lewy bodies (LBs) consisting largely of alpha-synuclein (alpha-syn), the protein mutated in some patients with familial PD. The mechanisms of alpha-syn fibrillization and LB formation are unknown, but may involve aberrant degradation or turnover. We examined the ability of calpain I to cleave alpha-syn in vitro. Calpain I cleaved wild-type alpha-syn predominantly after amino acid 57 and within the non-amyloid component (NAC) region. In contrast, calpain I cleaved fibrillized alpha-syn primarily in the region of amino acid 120 to generate fragments like those that increase susceptibility to dopamine toxicity and oxidative stress. Further, while calpain I cleaved wild-type alpha-syn after amino acid 57, this did not occur in mutant A53T alpha-syn. This paucity of proteolysis could increase the stability of A53T alpha-syn, suggesting that calpain I might protect cells from forming LBs by specific cleavages of soluble wild-type alpha-syn. However, once alpha-syn has polymerized into fibrils, calpain I may contribute to toxicity of these forms of alpha-syn by cleaving at aberrant sites within the C-terminal region. Elucidating the role of calpain I in the proteolytic processing of alpha-syn in normal and diseased brains may clarify mechanisms of neurodegenerative alpha-synucleinopathies.
帕金森病（PD）的特征是存在称为路易小体（LBs）的纤维状神经元内含物，其主要由α-突触核蛋白（α-syn）组成，该蛋白在一些家族性PD患者中发生突变。α-突触核蛋白纤维化和路易小体形成的机制尚不清楚，但可能涉及异常降解或周转。我们在体外检测了钙蛋白酶I切割α-突触核蛋白的能力。钙蛋白酶I主要在氨基酸57之后以及非淀粉样成分（NAC）区域内切割野生型α-突触核蛋白。相比之下，钙蛋白酶I主要在氨基酸120区域切割纤维化的α-突触核蛋白，以产生增加对多巴胺毒性和氧化应激敏感性的片段。此外，虽然钙蛋白酶I在氨基酸57之后切割野生型α-突触核蛋白，但在突变型A53Tα-突触核蛋白中并未发生这种情况。这种蛋白水解的缺乏可能会增加A53Tα-突触核蛋白的稳定性，这表明钙蛋白酶I可能通过特异性切割可溶性野生型α-突触核蛋白来保护细胞不形成路易小体。然而，一旦α-突触核蛋白聚合成纤维，钙蛋白酶I可能通过在C末端区域内的异常位点切割而导致这些形式的α-突触核蛋白产生毒性。阐明钙蛋白酶I在正常和患病大脑中α-突触核蛋白蛋白水解加工中的作用，可能会阐明神经退行性α-突触核蛋白病的机制。
