The Atg1–kinase complex tethers Atg9-vesicles to initiate autophagy

Abstract

Autophagosomes are double-membrane vesicles that sequester cytoplasmic material for lysosomal degradation. Their biogenesis is initiated by recruitment of Atg9-vesicles to the phagophore assembly site. This process depends on the regulated activation of the Atg1–kinase complex. However, the underlying molecular mechanism remains unclear. Here we reconstitute this early step in autophagy from purified components in vitro. We find that on assembly from its cytoplasmic subcomplexes, the Atg1–kinase complex becomes activated, enabling it to recruit and tether Atg9-vesicles. The scaffolding protein Atg17 targets the Atg1–kinase complex to autophagic membranes by specifically recognizing the membrane protein Atg9. This interaction is inhibited by the two regulatory subunits Atg31 and Atg29. Engagement of the Atg1–Atg13 subcomplex restores the Atg9-binding and membrane-tethering activity of Atg17. Our data help to unravel the mechanism that controls Atg17-mediated tethering of Atg9-vesicles, providing the molecular basis to understand initiation of autophagosome-biogenesis.

The molecular mechanism of Atg13 function in autophagy induction: What is hidden behind the data?

“…In contrast to Atg13, Atg17 does not bind lipid membranes. 6,7 In agreement with an earlier study, 8 Atg17 interacts with Atg9. Specifically, the central crescent (a4 helix) of Atg17 binds to the cytoplasmic domain (residues 424-507 in S. cerevisiae) and a short N-terminal region (residues 281-316 in S. cerevisiae) of Atg9.…”

“…Combining the results of Rao et al 6 and Yamamoto et al 11 in reverse chronological order along with the previous research yields a model of Atg13 function within the Atg1 complex for tethering an Atg9 vesicle (Fig. 1).…”

“…A recent report by Rao et al 6 significantly advanced our understanding of the function and structure of the Atg1 complex. This paper is the first study where this complex was reconstituted in vitro from purified components.…”

“…Binding of the Atg13[17LR] to the Atg17 dimer interface facilitates a pivoting movement of the Atg31-Atg29 subcomplex away from the center of the Atg17 crescent, which activates the Atg17-Atg31-Atg29 trimer and leads to the Atg9-Atg17 interaction. 6 Downstream from 17BR, the Atg13 IDR carries the inducible à alpha à -helical MITinteracting motif/MIM (460-521) that binds the MIT region of Atg1. The affinity of this interaction is also enhanced by dephosphorylation of phosphoserines in the MIT-interacting motif region.…”

Dual Roles of CD38 in Autophagy

“…Indeed, the autophagy process is executed by more than 30 Atg factors and associated proteins in response to stimuli. It is known that autophagy is initiated at the phagophore assembly site (PAS) in yeast [33]. Yamamoto et al demonstrated that the Atg13-mediated supramolecular assembly is responsible for autophagy initiation [34].…”