Precious B, Childs K, Fitzpatrick-Swallow V, Goodbourn S, Randall R E
School of Biology, University of St. Andrews, Fife KY16 9TS, United Kingdom.
J Virol. 2005 Nov;79(21):13434-41. doi: 10.1128/JVI.79.21.13434-13441.2005.
The V protein of simian virus 5 (SV5) facilitates the ubiquitination and subsequent proteasome-mediated degradation of STAT1. Here we show, by visualizing direct protein-protein interactions and by using the yeast two-hybrid system, that while the SV5 V protein fails to bind to STAT1 directly, it binds directly and independently to both DDB1 and STAT2, two cellular proteins known to be essential for SV5-mediated degradation of STAT1. We also demonstrate that STAT1 and STAT2 interact independently of SV5 V and show that SV5 V protein acts as an adaptor molecule linking DDB1 to STAT2/STAT1 heterodimers, which in the presence of additional accessory cellular proteins, including Cullin 4a, can ubiquitinate STAT1. Additionally, we show that the avidity of STAT2 for V is relatively weak but is significantly enhanced by the presence of both STAT1 and DDB1, i.e., the complex of STAT1, STAT2, DDB1, and SV5 V is more stable than a complex of STAT2 and V. From these studies we propose a dynamic model in which SV5 V acts as a bridge, bringing together a DDB1/Cullin 4a-containing ubiquitin ligase complex and STAT1/STAT2 heterodimers, which leads to the degradation of STAT1. The loss of STAT1 results in a decrease in affinity of binding of STAT2 for V such that STAT2 either dissociates from V or is displaced from V by STAT1/STAT2 complexes, thereby ensuring the cycling of the DDB1 and SV5 V containing E3 complex for continued rounds of STAT1 ubiquitination and degradation.
猴病毒5（SV5）的V蛋白促进信号转导和转录激活因子1（STAT1）的泛素化及随后蛋白酶体介导的降解。在此，我们通过可视化直接的蛋白质-蛋白质相互作用并使用酵母双杂交系统表明，虽然SV5 V蛋白不能直接与STAT1结合，但它能直接且独立地与损伤特异性DNA结合蛋白1（DDB1）和STAT2结合，这两种细胞蛋白已知对SV5介导的STAT1降解至关重要。我们还证明STAT1和STAT2的相互作用独立于SV5 V，并表明SV5 V蛋白作为一种衔接分子，将DDB1与STAT2/STAT1异二聚体连接起来，在存在包括Cullin 4a在内的其他辅助细胞蛋白时，该异二聚体可使STAT1泛素化。此外，我们表明STAT2对V的亲和力相对较弱，但在STAT1和DDB1同时存在时显著增强，即STAT1、STAT2、DDB1和SV5 V的复合物比STAT2和V的复合物更稳定。从这些研究中，我们提出了一个动态模型，其中SV5 V充当桥梁，将含DDB1/Cullin 4a的泛素连接酶复合物与STAT1/STAT2异二聚体聚集在一起，导致STAT1降解。STAT1的缺失导致STAT2与V结合亲和力降低，使得STAT2要么从V上解离，要么被STAT1/STAT2复合物从V上取代，从而确保含DDB1和SV5 V的E3复合物循环，以持续进行STAT1的泛素化和降解。
