Shanghai Center for Plant Stress Biology and Center of Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
University of the Chinese Academy of Sciences, Beijing 100049, China.
Plant Physiol. 2020 May;183(1):358-370. doi: 10.1104/pp.19.01417. Epub 2020 Mar 5.
N-terminal (Nt) acetylation (NTA) is an ample and irreversible cotranslational protein modification catalyzed by ribosome-associated Nt-acetyltransferases. NTA on specific proteins can act as a degradation signal (called an Ac/N-degron) for proteolysis in yeast and mammals. However, in plants, the biological relevance of NTA remains largely unexplored. In this study, we reveal that Arabidopsis () SIGMA FACTOR-BINDING PROTEIN1 (SIB1), a transcription coregulator and a positive regulator of salicylic acid-primed cell death, undergoes an absolute NTA on the initiator Met; Nt-acetyltransferase B (NatB) partly contributes to this modification. While NTA results in destabilization of certain target proteins, our genetic and biochemical analyses revealed that plant NatB-involved NTA instead renders SIB1 more stable. Given that the ubiquitin/proteasome system stimulates SIB1 degradation, it seems that the NTA-conferred stability ensures the timely expression of SIB1-dependent genes, mostly related to immune responses. Taking our findings together, here we report a noncanonical NTA-driven protein stabilization in land plants.
N 端（Nt）乙酰化（NTA）是一种广泛存在且不可逆的翻译共发生蛋白修饰，由核糖体相关的 Nt-乙酰转移酶催化。在酵母和哺乳动物中，特定蛋白质上的 NTA 可以作为蛋白水解的降解信号（称为 Ac/N-降解子）。然而，在植物中，NTA 的生物学相关性在很大程度上仍未得到探索。在本研究中，我们揭示了拟南芥（）SIGMA FACTOR-BINDING PROTEIN1（SIB1），一种转录共调节剂和水杨酸引发细胞死亡的正调节剂，在起始 Met 上经历绝对的 NTA；Nt-乙酰转移酶 B（NatB）部分促成了这种修饰。虽然 NTA 导致某些靶蛋白的不稳定性，但我们的遗传和生化分析表明，植物 NatB 参与的 NTA 反而使 SIB1 更稳定。鉴于泛素/蛋白酶体系统刺激 SIB1 的降解，似乎 NTA 赋予的稳定性确保了 SIB1 依赖性基因的及时表达，这些基因主要与免疫反应有关。综合我们的发现，我们在这里报告了在陆地植物中存在一种非典型的 NTA 驱动的蛋白稳定化机制。
