Department of Physiology, University of California, San Francisco, California, USA.
Department of Biochemistry & Biophysics, University of California, San Francisco, California, USA.
J Biol Chem. 2022 Nov;298(11):102560. doi: 10.1016/j.jbc.2022.102560. Epub 2022 Oct 4.
The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 is responsible for compaction of the ∼30-kb RNA genome in the ∼90-nm virion. Previous studies suggest that each virion contains 35 to 40 viral ribonucleoprotein (vRNP) complexes, or ribonucleosomes, arrayed along the genome. There is, however, little mechanistic understanding of the vRNP complex. Here, we show that N protein, when combined in vitro with short fragments of the viral genome, forms 15-nm particles similar to the vRNP structures observed within virions. These vRNPs depend on regions of N protein that promote protein-RNA and protein-protein interactions. Phosphorylation of N protein in its disordered serine/arginine region weakens these interactions to generate less compact vRNPs. We propose that unmodified N protein binds structurally diverse regions in genomic RNA to form compact vRNPs within the nucleocapsid, while phosphorylation alters vRNP structure to support other N protein functions in viral transcription.
严重急性呼吸综合征冠状病毒 2 的核衣壳 (N) 蛋白负责将 ∼30-kb 的 RNA 基因组在 ∼90-nm 的病毒粒子中压缩。先前的研究表明，每个病毒粒子包含 35 到 40 个病毒核糖核蛋白 (vRNP) 复合物，或核糖核小体，沿基因组排列。然而，对于 vRNP 复合物的机制理解甚少。在这里，我们表明 N 蛋白与病毒基因组的短片段在体外结合时，形成类似于病毒粒子中观察到的 vRNP 结构的 15-nm 颗粒。这些 vRNPs 依赖于促进蛋白质-RNA 和蛋白质-蛋白质相互作用的 N 蛋白区域。N 蛋白无序丝氨酸/精氨酸区域的磷酸化削弱了这些相互作用，从而产生不太紧凑的 vRNPs。我们提出，未修饰的 N 蛋白结合基因组 RNA 中结构多样的区域，在核衣壳内形成紧凑的 vRNPs，而磷酸化改变 vRNP 结构，以支持病毒转录过程中其他 N 蛋白的功能。
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