Cancer and Vascular Biology Research Center, The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa, Israel.
Cell Cycle. 2010 Feb 1;9(3):523-30. doi: 10.4161/cc.9.3.11152.
Ubiquitin (Ub), a centrally important component of the ubiquitin-proteasome system (UPS), is covalently attached to numerous cellular proteins through a highly regulated process. The attached Ub serves as a recognition element in trans, to which a variety of downstream effectors bind. These complexes play roles in a broad array of cellular functions, the best studied is targeting of the conjugated proteins to degradation by the 26S proteasome. Regulated degradation plays key roles in basic processes such as cell cycle, differentiation, transcription, and maintenance of the cellular quality control. In addition to its conjugated form, there is also a free pool of Ub that is essential to ascertain its immediate availability for the many tasks it serves. Ub is considered as a stable protein, particularly due to its unique globular structure and ability to be recycled by deubiquitinating enzymes (DUBs). However, alterations in its steady state which occur under different pathophysiological conditions have suggested more complex, yet elusive, regulatory mechanisms that govern Ub stability. Recent findings have demonstrated that Ub can be degraded by the proteasome via three routes along with its conjugated substrate, when extended with a C-terminal tail, and as a monomer.
泛素（Ub）是泛素蛋白酶体系统（UPS）的一个重要组成部分，通过高度调控的过程共价连接到许多细胞蛋白上。附着的 Ub 作为一个识别元件，与各种下游效应物结合。这些复合物在广泛的细胞功能中发挥作用，其中研究最多的是将共轭蛋白靶向到 26S 蛋白酶体进行降解。受调控的降解在基本过程中起着关键作用，如细胞周期、分化、转录和细胞质量控制的维持。除了其共轭形式外，还有一个游离的 Ub 池，这对于确保其立即用于其众多功能是必不可少的。Ub 被认为是一种稳定的蛋白质，特别是由于其独特的球状结构和被去泛素化酶（DUBs）回收的能力。然而，在不同病理生理条件下其稳态的改变表明了更复杂但难以捉摸的调节机制来控制 Ub 的稳定性。最近的研究发现，Ub 可以通过三种途径与它的共轭底物一起被蛋白酶体降解，当延长 C 末端尾巴时，以及作为单体。
