Unconventional initiation of PINK1/Parkin mitophagy by Optineurin
Thanh Ngoc Nguyen, Justyna Sawa‐Makarska, Grace Khuu, Wai Kit Lam, Elias Adriaenssens, Dorotea Fracchiolla, Stephen Shoebridge, Daniel Bernklau, Benjamin Scott Padman, Marvin Skulsuppaisarn, Runa Lindblom, Sascha Martens, Michael Lazarou
Abstract
Cargo sequestration is a fundamental step of selective autophagy in which cells generate a double-membrane structure termed an "autophagosome" on the surface of cargoes. NDP52, TAX1BP1, and p62 bind FIP200, which recruits the ULK1/2 complex to initiate autophagosome formation on cargoes. How OPTN initiates autophagosome formation during selective autophagy remains unknown despite its importance in neurodegeneration. Here, we uncover an unconventional path of PINK1/Parkin mitophagy initiation by OPTN that does not begin with FIP200 binding or require the ULK1/2 kinases. Using gene-edited cell lines and in vitro reconstitutions, we show that OPTN utilizes the kinase TBK1, which binds directly to the class III phosphatidylinositol 3-kinase complex I to initiate mitophagy. During NDP52 mitophagy initiation, TBK1 is functionally redundant with ULK1/2, classifying TBK1's role as a selective autophagy-initiating kinase. Overall, this work reveals that OPTN mitophagy initiation is mechanistically distinct and highlights the mechanistic plasticity of selective autophagy pathways.