UC San Diego

Peroxisomes are important single membrane organelles which are required for certain metabolic pathways. In yeast, Pichia pastoris, peroxisomes are degraded by selective autophagy pathway termed pexophagy. Autophagy is process whereby proteins and organelles are delivered to the vacuole and degraded. Previous studies indicated Atg30 as the receptor for pexophagy, which interacts with the autophagic machinery (Atg11 and Atg17) as well as peroxisomal membrane (Pex3 and Pex14). However, unlike other selective autophagy receptors, Atg30 does not interact with Atg8, a major component of the isolation membrane that sequester peroxisomes during pexophagy. Here, we found the missing link, a novel peroxisomal membrane protein Rppa09976, which bridges peroxisomal (Pex3 and Atg30) and isolation (Atg8) membranes. Rppa09976 is phosphoprotein that contains an N-terminal acyl-CoA binding domain, three putative Atg8 binding sites and two transmembrane domains. Rppa09976 is expressed in methanol medium and phosphorylated upon arrival to peroxisomes from ER. We purified the Rppa09976-HA fusion protein and mapped 21 phosphorylation sites by mass spectrometry. The functional role of Rppa09976 phosphorylation awaits further studies. We showed that two of the three putative Atg8 binding sites at the N-terminal of the protein are required for Atg8 binding and pexophagy. Point mutation of the conserved acyl-CoA binding site also leads to a pexophagy defect. Hence, we propose that Rppa09976 provides acyl-CoA for the growing isolation membranes that sequester peroxisomes