Gladding R L, Haas A L, Gronros D L, Lawson T G
Department of Chemistry, Bates College, Lewiston, Maine 04240, USA.
Biochem Biophys Res Commun. 1997 Sep 8;238(1):119-25. doi: 10.1006/bbrc.1997.7251.
The picornavirus 3C proteases are required for the processing of viral polyproteins during infections of host cells. Here we report that the 3C protease of the hepatitis A virus, like that of the encephalomyocarditis virus, is a substrate for rapid, ubiquitin-mediated degradation in vitro. Ubiquitin was shown to stimulate the turnover of the hepatitis virus 3C protease, and labeled protease was found to become incorporated into a mixture of high molecular weight species, which is characteristic of conjugation with polyubiquitin chains. In the presence of methylated ubiquitin, a new 33 kDa species formed, consistent with the generation of a monoubiquitin-3C protease conjugate. The rate of degradation of the 3C protease was reduced by inhibitors of the 26S proteasome. A similar evaluation of the 3C protease of poliovirus revealed that it is stable protein and is not conjugated with ubiquitin. It was also determined that the hepatitis A and encephalomyocarditis virus 3C proteases compete with each other for conjugation with ubiquitin and for degradation. This suggests that the two 3C proteases are both recognized by the same ubiquitin system enzyme, or enzymes, responsible for selecting them as targets for destruction.
微小核糖核酸病毒3C蛋白酶在宿主细胞感染期间对病毒多聚蛋白的加工是必需的。在此我们报道，甲型肝炎病毒的3C蛋白酶与脑心肌炎病毒的3C蛋白酶一样，在体外是快速的、泛素介导降解的底物。已表明泛素能刺激甲型肝炎病毒3C蛋白酶的周转，并且发现标记的蛋白酶会掺入高分子量物质的混合物中，这是与多聚泛素链缀合的特征。在甲基化泛素存在的情况下，形成了一种新的33 kDa物质，这与单泛素-3C蛋白酶缀合物的产生一致。26S蛋白酶体抑制剂降低了3C蛋白酶的降解速率。对脊髓灰质炎病毒3C蛋白酶的类似评估表明，它是一种稳定的蛋白质，不与泛素缀合。还确定甲型肝炎病毒和脑心肌炎病毒3C蛋白酶在与泛素缀合及降解方面相互竞争。这表明这两种3C蛋白酶都被负责将它们选为破坏靶标的相同泛素系统酶或多种酶所识别。
