Functions of PI4P and Sterol Glucoside Necessary for the Synthesis of a Nascent Membrane Structure During Pexophagy

We recently showed that, in the yeast Pichia pastoris, an ergosterol glucoside synthesizing enzyme Atg26 is recruited to the precursor of the pexophagic structure, micropexophagic membrane apparatus (MIPA), under the regulation of phosphatidylinositol 4'-monophosphate (PI4P)-signaling during pexophagy. Atg26 was found to harbor a novel PI4P-binding motif, GRAM domain. Both lipids, PI4P and sterol glucoside, synthesized by PpPik1 and PpAtg26, respectively, were necessary for pexophagy, in the step where the MIPA was formed. In this addendum, we review these findings, and speculate the mechanistic and physiological implications of the functions of these lipids during the autophagic process.Addendum to:PI4P-Signaling Pathway for the Synthesis of a Nascent Membrane Structure in Selective AutophagyS. Yamashita, M. Oku, Y. Wasada, Y. Ano and Y. SakaiJ Cell Biol 2006; 173: 709-17