Lim Kah Leong, Chew Katherine C M, Tan Jeanne M M, Wang Cheng, Chung Kenny K K, Zhang Yi, Tanaka Yuji, Smith Wanli, Engelender Simone, Ross Christopher A, Dawson Valina L, Dawson Ted M
Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Neurosci. 2005 Feb 23;25(8):2002-9. doi: 10.1523/JNEUROSCI.4474-04.2005.
It is widely accepted that the familial Parkinson's disease (PD)-linked gene product, parkin, functions as a ubiquitin ligase involved in protein turnover via the ubiquitin-proteasome system. Substrates ubiquitinated by parkin are hence thought to be destined for proteasomal degradation. Because we demonstrated previously that parkin interacts with and ubiquitinates synphilin-1, we initially expected synphilin-1 degradation to be enhanced in the presence of parkin. Contrary to our expectation, we found that synphilin-1 is normally ubiquitinated by parkin in a nonclassical, proteasomal-independent manner that involves lysine 63 (K63)-linked polyubiquitin chain formation. Parkin-mediated degradation of synphilin-1 occurs appreciably only at an unusually high parkin to synphilin-1 expression ratio or when primed for lysine 48 (K48)-linked ubiquitination. In addition we found that parkin-mediated ubiquitination of proteins within Lewy-body-like inclusions formed by the coexpression of synphilin-1, alpha-synuclein, and parkin occurs predominantly via K63 linkages and that the formation of these inclusions is enhanced by K63-linked ubiquitination. Our results suggest that parkin is a dual-function ubiquitin ligase and that K63-linked ubiquitination of synphilin-1 by parkin may be involved in the formation of Lewy body inclusions associated with PD.
人们普遍认为，与家族性帕金森病（PD）相关的基因产物parkin作为一种泛素连接酶，通过泛素 - 蛋白酶体系统参与蛋白质周转。因此，被parkin泛素化的底物被认为会被蛋白酶体降解。因为我们之前证明了parkin与synphilin - 1相互作用并使其泛素化，所以我们最初预期在有parkin存在的情况下，synphilin - 1的降解会增强。与我们的预期相反，我们发现synphilin - 1通常以一种非经典的、不依赖蛋白酶体的方式被parkin泛素化，这种方式涉及赖氨酸63（K63）连接的多聚泛素链形成。Parkin介导的synphilin - 1降解仅在parkin与synphilin - 1表达比例异常高时或在被赖氨酸48（K48）连接的泛素化引发时才会明显发生。此外，我们发现由synphilin - 1、α - 突触核蛋白和parkin共表达形成的路易小体样包涵体内蛋白质的parkin介导的泛素化主要通过K63连接发生，并且这些包涵体的形成会因K63连接的泛素化而增强。我们的结果表明parkin是一种具有双重功能的泛素连接酶，并且parkin对synphilin - 1的K63连接的泛素化可能参与了与PD相关的路易小体包涵体的形成。
