Tsvetkov Peter, Reuven Nina, Prives Carol, Shaul Yosef
Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
J Biol Chem. 2009 Sep 25;284(39):26234-42. doi: 10.1074/jbc.M109.040493. Epub 2009 Jul 17.
The N-terminal transcription activation domain of p53 is intrinsically unstructured. We show in vitro and in vivo that this domain initiates p53 degradation by the 20 S proteasome in a ubiquitin-independent fashion. The decay of metabolically labeled p53 follows biphasic kinetics with an immediate fast phase that is ubiquitin-independent and a second slower phase that is ubiquitin-dependent. The 20 S proteasome executes the first phase by default, whereas the second phase requires the 26 S proteasome. p53 N-terminal binding proteins, such as Hdmx, can selectively block the first phase of degradation. Remarkably, gamma-irradiation inhibits both p53 decay phases, whereas UV selectively negates the second phase, giving rise to discrete levels of p53 accumulation. Our data of a single protein experiencing double mode degradation mechanisms each with unique kinetics provide the mechanistic basis for programmable protein homeostasis (proteostasis).
p53的N端转录激活结构域本质上是无序的。我们在体外和体内均表明，该结构域以不依赖泛素的方式启动20S蛋白酶体介导的p53降解。代谢标记的p53的降解遵循双相动力学，即一个快速的初始阶段不依赖泛素，以及一个较慢的第二阶段依赖泛素。20S蛋白酶体默认执行第一阶段，而第二阶段则需要26S蛋白酶体。p53的N端结合蛋白，如Hdmx，可以选择性地阻断降解的第一阶段。值得注意的是，γ射线照射可抑制p53降解的两个阶段，而紫外线则选择性地消除第二阶段，从而导致p53积累水平的差异。我们关于单一蛋白质经历具有独特动力学的双模式降解机制的数据，为可编程蛋白质稳态（蛋白质平衡）提供了机制基础。
