PDF(Pubmed)
Abstract：
The proteasome controls levels of most cellular proteins, and its activity is regulated under stress, quiescence, and inflammation. However, factors determining the proteasomal degradation rate remain poorly understood. Proteasome substrates are conjugated with small proteins (tags) like ubiquitin and Fat10 to target them to the proteasome. It is unclear if the structural plasticity of proteasome-targeting tags can influence substrate degradation. Fat10 is upregulated during inflammation, and its substrates undergo rapid proteasomal degradation. We report that the degradation rate of Fat10 substrates critically depends on the structural plasticity of Fat10. While the ubiquitin tag is recycled at the proteasome, Fat10 is degraded with the substrate. Our results suggest significantly lower thermodynamic stability and faster mechanical unfolding in Fat10 compared to ubiquitin. Long-range salt bridges are absent in the Fat10 structure, creating a plastic protein with partially unstructured regions suitable for proteasome engagement. Fat10 plasticity destabilizes substrates significantly and creates partially unstructured regions in the substrate to enhance degradation. NMR-relaxation-derived order parameters and temperature dependence of chemical shifts identify the Fat10-induced partially unstructured regions in the substrate, which correlated excellently to Fat10-substrate contacts, suggesting that the tag-substrate collision destabilizes the substrate. These results highlight a strong dependence of proteasomal degradation on the structural plasticity and thermodynamic properties of the proteasome-targeting tags.
摘要：
蛋白酶体控制大多数细胞蛋白质的水平，它的活动在压力下受到调节，静止,和炎症。然而,决定蛋白酶体降解率的因素仍然知之甚少。蛋白酶体底物与小蛋白(标签)如泛素和Fat10缀合,以将它们靶向蛋白酶体。目前尚不清楚蛋白酶体靶向标签的结构可塑性是否会影响底物降解。Fat10在炎症期间上调，其底物经历快速的蛋白酶体降解。我们报告说，Fat10底物的降解速率关键取决于Fat10的结构可塑性。虽然泛素标记在蛋白酶体被回收，Fat10随底物降解。我们的结果表明，与泛素相比，Fat10的热力学稳定性明显降低，机械解折叠更快。Fat10结构中不存在长程盐桥，创造一种具有部分非结构化区域的塑料蛋白质，适合蛋白酶体接合。FatlO可塑性显著地使基材不稳定并在基材中产生部分非结构化区域以增强降解。NMR弛豫衍生的有序参数和化学位移的温度依赖性确定了Fat10诱导的部分非结构化区域，与Fat10-底物接触非常相关，这表明标签-底物碰撞使底物不稳定。这些结果突出了蛋白酶体降解对蛋白酶体靶向标签的结构可塑性和热力学性质的强烈依赖性。
