Clearance of biomolecular condensates by selective autophagy is thought to play a crucial role in cellular homeostasis. However, the mechanism underlying selective autophagy of condensates and whether liquidity determines a condensate's susceptibility to degradation by autophagy remain unknown. Here, we show that the selective autophagic cargo aminopeptidase I (Ape1) undergoes phase separation to form semi-liquid droplets. The Ape1-specific receptor protein Atg19 localizes to the surface of Ape1 droplets both in vitro and in vivo, with the "floatability" of Atg19 preventing its penetration into droplets. In vitro reconstitution experiments reveal that Atg19 and lipidated Atg8 are necessary and sufficient for selective sequestration of Ape1 droplets by membranes. This sequestration is impaired by mutational solidification of Ape1 droplets or diminished ability of Atg19 to float. Taken together, we propose that cargo liquidity and the presence of sufficient amounts of autophagic receptor on cargo are crucial for selective autophagy of biomolecular condensates.

中文翻译：

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流动性是蛋白质冷凝物选择性自噬的关键决定因素。

通过选择性自噬清除生物分子冷凝物被认为在细胞体内平衡中起着至关重要的作用。但是，凝结水选择性自噬的基础机理以及流动性是否决定凝结水通过自噬降解的敏感性尚不清楚。在这里，我们显示选择性自噬货物氨肽酶I（Ape1）经历相分离形成半液滴。Ape1特异性受体蛋白Atg19在体内和体外均位于Ape1液滴的表面，而Atg19的“漂浮性”阻止其渗透到液滴中。体外重建实验表明，Atg19和脂化的Atg8对于通过膜选择性隔离Ape1液滴是必要和充分的。Ape1小滴的突变固化或Atg19漂浮的能力减弱会削弱这种螯合作用。两者合计，我们认为货物的流动性和货物上足够数量的自噬受体的存在对于生物分子缩合物的选择性自噬至关重要。