Ubiquitination of the yeast receptor Atg32 modulates mitophagy

Mitophagy, the process that degrades mitochondria selectively through autophagy, is involved in the quality control of these organelles. In yeast, the presence of the Atg32 protein on the outer mitochondrial membrane allows for the recognition and targeting of superfluous or damaged mitochondria for degradation. Some posttranslational modifications, such as phosphorylation, are crucial for the execution of the mitophagy process. In our study, we showed that in the stationary phase of growth, and to a lesser extent during starvation, the Atg32 protein level decreases. The fact that a decline in Atg32 level can be prevented by inhibition of the proteolytic activity of proteasome may indicate that Atg32 is also ubiquitylated. In fact, mass spectrometry analysis of purified Atg32 protein showed ubiquitination of lysine residue in position 282. These different patterns of posttranslational modifications of Atg32 could allow cells to control the mitophagy process carefully.