Architecture and Dynamics of the Autophagic ATG2-ATG18 Complex

Abstract

Autophagy is a highly regulated process of degradation and recycling of cellular components and pathogens. Hallmark of autophagy is formation of a double-membrane cytosolic vesicles, termed autophagosomes, which sequester cytoplasm and delivers it to the lysosome where it is degraded and recycled. Nucleation and expansion of autophagic membranes require recruitment of autophagy related protein 2 (ATG2) and phosphatidylinositol-3-phosphate (PI3P) effector protein ATG18 to the pre-autophagosomal structure (PAS). We used single-particle electron microscopy, structural proteomics and biochemical analyses to characterize S. cerevisiae ATG2 in complex with the ATG18. ATG2 has an elongated, rod-shaped structure and can exist as an antiparallel dimer or as a monomer with the ATG18 bound at one of the ends. Liposome binding experiments have been used to characterize the affinity of the ATG2-ATG18 complex for different lipids and cooperativity between the subunits as a possible mechanism for membrane recruitment and vesicle tethering, shedding light on its targeting to the PAS. Furthermore, we performed hydrogen-deuterium exchange mass spectrometry (HDX-MS) and identified a localized change in conformational dynamics upon complex formation. This provides one of the first structural insights into the ATG2-ATG18 complex and its membrane interaction mechanism and explores molecular mechanisms involved in the early steps of autophagosome biogenesis.