Bennett M C, Bishop J F, Leng Y, Chock P B, Chase T N, Mouradian M M
Experimental Therapeutics Branch, NINDS, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 1999 Nov 26;274(48):33855-8. doi: 10.1074/jbc.274.48.33855.
Mutations in alpha-synuclein are known to be associated with Parkinson's disease (PD). The coexistence of this neuronal protein with ubiquitin and proteasome subunits in Lewy bodies in sporadic disease suggests that alterations of alpha-synuclein catabolism may contribute to the pathogenesis of PD. The degradation pathway of alpha-synuclein has not been identified nor has the kinetics of this process been described. We investigated the degradation kinetics of both wild-type and A53T mutant 6XHis-tagged alpha-synuclein in transiently transfected SH-SY5Y cells. Degradation of both isoforms followed first-order kinetics over 24 h as monitored by the pulse-chase method. However, the t((1)/(2)) of mutant alpha-synuclein was 50% longer than that of the wild-type protein (p < 0.01). The degradation of both recombinant proteins and endogenous alpha-synuclein in these cells was blocked by the selective proteasome inhibitor beta-lactone (40 microM), indicating that both wild-type and A53T mutant alpha-synuclein are degraded by the ubiquitin-proteasome pathway. The slower degradation of mutant alpha-synuclein provides a kinetic basis for its intracellular accumulation, thus favoring its aggregation.
已知α-突触核蛋白的突变与帕金森病（PD）相关。在散发性疾病的路易小体中，这种神经元蛋白与泛素和蛋白酶体亚基共存，这表明α-突触核蛋白分解代谢的改变可能有助于PD的发病机制。α-突触核蛋白的降解途径尚未确定，该过程的动力学也未被描述。我们研究了野生型和A53T突变体6XHis标记的α-突触核蛋白在瞬时转染的SH-SY5Y细胞中的降解动力学。通过脉冲追踪法监测，两种异构体的降解在24小时内均遵循一级动力学。然而，突变型α-突触核蛋白的t（1/2）比野生型蛋白长50%（p<0.01）。这些细胞中重组蛋白和内源性α-突触核蛋白的降解被选择性蛋白酶体抑制剂β-内酯（40μM）阻断，表明野生型和A53T突变型α-突触核蛋白均通过泛素-蛋白酶体途径降解。突变型α-突触核蛋白较慢的降解为其细胞内积累提供了动力学基础，从而有利于其聚集。
