Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS One. 2009 Dec 29;4(12):e8477. doi: 10.1371/journal.pone.0008477.
Beta-site APP cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease with a lumenal active site that sheds the ectodomains of membrane proteins through juxtamembrane proteolysis. BACE1 has been studied principally for its role in Alzheimer's disease as the beta-secretase responsible for generating the amyloid-beta protein. Emerging evidence from mouse models has identified the importance of BACE1 in myelination and cognitive performance. However, the substrates that BACE1 processes to regulate these functions are unknown, and to date only a few beta-secretase substrates have been identified through candidate-based studies. Using an unbiased approach to substrate identification, we performed quantitative proteomic analysis of two human epithelial cell lines stably expressing BACE1 and identified 68 putative beta-secretase substrates, a number of which we validated in a cell culture system. The vast majority were of type I transmembrane topology, although one was type II and three were GPI-linked proteins. Intriguingly, a preponderance of these proteins are involved in contact-dependent intercellular communication or serve as receptors and have recognized roles in the nervous system and other organs. No consistent sequence motif predicting BACE1 cleavage was identified in substrates versus non-substrates. These findings expand our understanding of the proteins and cellular processes that BACE1 may regulate, and suggest possible mechanisms of toxicity arising from chronic BACE1 inhibition.
β-位点 APP 裂解酶 1（BACE1）是一种跨膜天冬氨酸蛋白酶，具有腔内活性位点，通过近膜蛋白水解作用去除膜蛋白的胞外结构域。BACE1 主要因其在阿尔茨海默病中的作用而被研究，作为负责生成淀粉样蛋白-β 蛋白的β-分泌酶。来自小鼠模型的新证据表明 BACE1 在髓鞘形成和认知表现中的重要性。然而，BACE1 处理以调节这些功能的底物尚不清楚，迄今为止，仅通过基于候选的研究鉴定了少数β-分泌酶底物。我们采用无偏方法对两种稳定表达 BACE1 的人上皮细胞系进行了定量蛋白质组学分析，鉴定了 68 种潜在的β-分泌酶底物，其中一些在细胞培养系统中得到了验证。绝大多数具有 I 型跨膜拓扑结构，尽管有一种是 II 型，三种是 GPI 连接蛋白。有趣的是，这些蛋白质中的绝大多数参与细胞间接触依赖性通讯，或作为受体，并在神经系统和其他器官中具有公认的作用。在底物与非底物中，未发现预测 BACE1 切割的一致序列基序。这些发现扩展了我们对 BACE1 可能调节的蛋白质和细胞过程的理解，并提示了慢性 BACE1 抑制可能产生的毒性的可能机制。
