Lipid mediated–phase separation of AGO proteins on ER controls nascent peptide ubiquitination

AGO/miRNA-mediated gene silencing and ubiquitin-mediated protein quality control represent two fundamental mechanisms that control proper gene expression. Here we unexpectedly discover that fly and human AGO proteins, key components in the miRNA pathway, undergo lipid-mediated phase separation and condense into RNP-granules on the endoplasmic reticulum (ER) membrane to control protein production. Phase separation on the ER is mediated by electrostatic interactions between a conserved lipid-binding motif within the AGOs and the lipid PI(4,5)P2. The ER-localized AGO condensates recruit the E3 ubiquitin ligase Ltn1 to catalyze nascent peptide ubiquitination and coordinate with the VCP-Ufd1-Npl4 complex to process unwanted protein products for proteasomal degradation. Collectively, our study provides insight into the understanding of post-transcription-translation coupling controlled by AGOs via lipid-mediated phase separation.

AGO/miRNA介导的基因沉默和泛素化介导的蛋白质质量调控是调控基因表达的两个基本机制。本研究意外发现，果蝇和人类的AGO蛋白，作为miRNA通路中的关键组分，在脂质介导的相分离过程中聚集于内质网（ER）膜上，形成RNP-颗粒，以调控蛋白质合成。内质网上的相分离过程由AGO蛋白中保守的脂质结合基序与脂质PI(4,5)P2之间的静电相互作用介导。定位于内质网的AGO颗粒招募E3泛素连接酶Ltn1，催化新生肽段的泛素化，并与VCP-Ufd1-Npl4复合体协调，处理不必要的蛋白质产物，以进行蛋白酶体降解。总体而言，本研究揭示了通过脂质介导的相分离，AGO蛋白如何控制转录后-翻译偶联的机制。