Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates.

During PINK1- and Parkin-mediated mitophagy, autophagy adaptors are recruited to damaged mitochondria to promote their selective degradation. Autophagy adaptors such as optineurin (OPTN) and NDP52 facilitate mitophagy by recruiting the autophagy-initiation machinery, and assisting engulfment of damaged mitochondria through binding to ubiquitinated mitochondrial proteins and autophagosomal ATG8 family proteins. Here, we demonstrate that OPTN and NDP52 form sheet-like phase-separated condensates with liquid-like properties on the surface of ubiquitinated mitochondria. The dynamic and liquid-like nature of OPTN condensates is important for mitophagy activity, because reducing the fluidity of OPTN-ubiquitin condensates suppresses the recruitment of ATG9 vesicles and impairs mitophagy. Based on these results, we propose a dynamic liquid-like, rather than a stoichiometric, model of autophagy adaptors to explain the interactions between autophagic membranes (i.e., ATG9 vesicles and isolation membranes) and mitochondrial membranes during Parkin-mediated mitophagy. This model underscores the importance of liquid-liquid phase separation in facilitating membrane-membrane contacts, likely through the generation of capillary forces. Synopsis: Autophagy adaptors undergo liquid-liquid phase separation, but it remains unclear how this contributes to selective mitochondrial autophagy. This study shows that the mitophagy adaptors OPTN and NDP52 phase-separate to facilitate mitochondrial recognition and mitophagy. OPTN and NDP52 form sheet-like condensates on ubiquitinated mitochondria during Parkin-mediated mitophagy. The liquid-like property of these adaptor condensates is important for mitophagy. Capillary forces of these condensates between mitochondria and autophagic membranes (i.e., ATG9 vesicles and isolation membranes) are likely to promote the attachment of these membranes. Damaged mitochondria are engulfed by autophagosomes through adhesive forces generated by wetting. [ABSTRACT FROM AUTHOR]