To degrade or not to degrade: how phase separation modulates selective autophagy

Selective macroautophagy/autophagy relies on newly formed double-membrane compartments, known as phagophores, to sequester and recycle diverse cellular components, including organelles, biomolecular condensates and protein aggregates, maturing into autophagosomes that fuse with the vacuole/lysosome. Autophagosomes originate at the cargo-vacuole/ER interface, where autophagy factors assemble into the phagophore assembly site (PAS). However, how autophagy proteins organize on the surface of structurally and biophysically different cargoes, and achieve spatial confinement at the PAS to support autophagosome formation remains unclear. Mechanisms governing cargo selection are also poorly understood. In this study, we demonstrate that receptor mobility, driven by low affinity cargo-receptor interactions, is crucial for rendering cellular structures degradable by autophagy. We show that cargo surface mobility, combined with the phase separation of scaffold proteins, drives the formation of early PAS precursors, termed "initiation hubs". These hubs dynamically rearrange at the cargo-vacuole/ER interface to promote autophagosome biogenesis, providing new insights into selective autophagy initiation.<b>Abbreviation:</b> Ape1: aminopeptidase I; Atg: autophagy related; Cvt pathway: cytoplasm-to-vacuole targeting pathway; GBP-GFP: GFP binding protein-Green Fluorescent Protein; ENDs: Ede1-dependent endocytic protein deposits; ER: endoplasmic reticulum; PAS: phagophore-assembly site; RB1CC1/FIP200: RB1-inducible coiled-coil 1; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like kinase 1.