Receptor-cargo coupling during ER-autophagy depends on coat proteins and ER membrane properties

Selective autophagy of the endoplasmic reticulum (reticulophagy) is driven by receptor-mediated ER remodeling. Reticulophagy receptors are essential for ER turnover. Productive cargo recognition during autophagosome-mediated reticulophagy depends on the interaction of the receptor with the COPII subunit Sfb3/Lst1 (SEC24C in mammals) as well as the phospholipid composition of the ER. We unexpectedly found that the conserved reticulophagy receptor Atg40 traffics to the vacuole/lysosome without cargo (ER membrane proteins) or Sfb3/Lst1 in neutral lipid-deficient mutant cells. Comprehensive lipidomic profiling of this lipid mutant revealed a shift in the phosphatidylethanolamine (PE)-to-phosphatidylcholine (PC) ratio, a compositional change predicted to alter biophysical properties of the ER, including membrane bendability. The discovery that membrane properties regulate receptor - cargo coupling efficiency at autophagic sites, as they do at secretory exit sites, extends current mechanistic models of reticulophagy and suggests membrane properties may also affect cargo selection on other types of selective autophagy pathways.