The PKA Signaling Pathway Regulates the Association of the Autophagy Initiation Complex With the Lipidation Machinery

A key step in autophagy is the conjugation by the E3-like Atg12-Atg5-Atg16 complex of the ubiquitin-like protein Atg8 to phosphatidylethanolamine on the autophagosomal membrane, a process known as lipidation. Previous work in yeast showed that recruitment of the E3-like complex to the preautophagosomal structure is mediated by the interaction of Atg16 with the phosphatidylinositol 3-phosphate-binding protein Atg21, and by the association of Atg12 with the scaffold protein of the Atg1 kinase complex, Atg17. Here, we conducted a reverse two-hybrid screen to identify residues in Atg17 and Atg12 critical for Atg17-Atg12 binding, and used these data to generate a docking model of Atg12-Atg5-Atg16 with the Atg17 complex. In this model, a conserved alpha-helix in the N-terminal region of Atg12 binds to the convex side of crescent-shaped Atg17 and appears to form a four-helix bundle with the three helices of Atg17, similar to that described for the binding of Atg31 to Atg17. We further showed that, in agreement with previous work, Atg17-Atg12 and Atg21-Atg16 binding act cooperatively to mediate the recruitment of the E3-like complex, although our results show that alternative mechanisms are involved in this process. Finally, we found that phosphorylation of Atg12 by PKA prevents its interaction with Atg17, thus adding a new regulatory layer in the control of autophagy by the PKA signaling pathway.