Daskalogianni Chrysoula, Apcher Sébastien, Candeias Marco M, Naski Nadia, Calvo Fabien, Fåhraeus Robin
INSERM U716, Institut de Génétique Moléculaire, Université Paris 7, Hôpital St. Louis, 75010 Paris, France.
J Biol Chem. 2008 Oct 31;283(44):30090-100. doi: 10.1074/jbc.M803290200. Epub 2008 Aug 29.
Partial degradation or regulated ubiquitin proteasome-dependent processing by the 26 S proteasome has been demonstrated, but the underlying molecular mechanisms and the prevalence of this phenomenon remain obscure. Here we show that the Gly-Ala repeat (GAr) sequence of EBNA1 affects processing of substrates via the ubiquitin-dependent degradation pathway in a substrate- and position-specific fashion. GAr-mediated increase in stability of proteins targeted for degradation via the 26 S proteasome was associated with a fraction of the substrates being partially processed and the release of the free GAr. The GAr did not cause a problem for the proteolytic activity of the proteasome, and its fusion to the N terminus of p53 resulted in an increase in the rate of degradation of the entire chimera. Interestingly the GAr had little effect on the stability of EBNA1 protein itself, and targeting EBNA1 for 26 S proteasome-dependent degradation led to its complete degradation. Taken together, our data suggest a model in which the GAr prevents degradation or promotes endoproteolytic processing of substrates targeted for the 26 S proteasome by interfering with the initiation step of substrate unfolding. These results will help to further understand the underlying mechanisms for partial proteasome-dependent degradation.
已有研究表明，EBNA1的甘氨酸-丙氨酸重复序列（GAr）可通过泛素依赖性降解途径，以底物和位置特异性的方式影响底物的加工过程。但这种现象的潜在分子机制和普遍程度仍不清楚。我们的研究表明，EBNA1的甘氨酸-丙氨酸重复序列（GAr）可通过泛素依赖性降解途径，以底物和位置特异性的方式影响底物的加工过程。GAr介导的通过26S蛋白酶体靶向降解的蛋白质稳定性增加，与一部分底物被部分加工以及游离GAr的释放有关。GAr对蛋白酶体的蛋白水解活性没有造成问题，并且将其与p53的N末端融合导致整个嵌合体的降解速率增加。有趣的是，GAr对EBNA1蛋白本身的稳定性影响很小，并且将EBNA1靶向26S蛋白酶体依赖性降解会导致其完全降解。综上所述，我们的数据提出了一个模型，其中GAr通过干扰底物解折叠的起始步骤，阻止靶向26S蛋白酶体的底物降解或促进其内切蛋白水解加工。这些结果将有助于进一步理解部分蛋白酶体依赖性降解的潜在机制。
