Boutell Chris, Sadis Seth, Everett Roger D
Medical Research Council Virology Unit, Glasgow G11 5JR, Scotland, United Kingdom.
J Virol. 2002 Jan;76(2):841-50. doi: 10.1128/jvi.76.2.841-850.2002.
Proteasome-dependent degradation of ubiquitinated proteins plays a key role in many important cellular processes. Ubiquitination requires the E1 ubiquitin activating enzyme, an E2 ubiquitin conjugating enzyme, and frequently a substrate-specific ubiquitin protein ligase (E3). One class of E3 ubiquitin ligases has been shown to contain a common zinc-binding RING finger motif. We have previously shown that herpes simplex virus type 1 ICP0, itself a RING finger protein, induces the proteasome-dependent degradation of several cellular proteins and induces the accumulation of colocalizing conjugated ubiquitin in vivo. We now report that both full-length ICP0 and its isolated RING finger domain induce the accumulation of polyubiquitin chains in vitro in the presence of E1 and the E2 enzymes UbcH5a and UbcH6. Mutations within the RING finger region that abolish the in vitro ubiquitination activity also cause severe reductions in ICP0 activity in other assays. We conclude that ICP0 has the potential to act as an E3 ubiquitin ligase during viral infection and to target specific cellular proteins for destruction by the 26S proteasome.
蛋白酶体依赖的泛素化蛋白降解在许多重要的细胞过程中起着关键作用。泛素化需要E1泛素激活酶、E2泛素结合酶，并且通常还需要底物特异性泛素蛋白连接酶（E3）。一类E3泛素连接酶已被证明含有常见的锌结合环指基序。我们之前已经表明，单纯疱疹病毒1型ICP0本身是一种环指蛋白，可诱导几种细胞蛋白的蛋白酶体依赖性降解，并在体内诱导共定位的共轭泛素的积累。我们现在报告，在E1以及E2酶UbcH5a和UbcH6存在的情况下，全长ICP0及其分离的环指结构域在体外均可诱导多聚泛素链的积累。环指区域内消除体外泛素化活性的突变在其他实验中也会导致ICP0活性严重降低。我们得出结论，ICP0在病毒感染期间有可能作为E3泛素连接酶，并将特定的细胞蛋白靶向26S蛋白酶体进行破坏。
