Atg15 is a vacuolar phospholipase that disintegrates organelle membranes

Abstract

Atg15 (autophagy-related 15) is a vacuolar phospholipase essential for the degradation of cytoplasm-to-vacuole targeting (Cvt) bodies and autophagic bodies, hereinafter referred to as intravacuolar autophagic compartments (IACs), but it remains unknown if Atg15 directly disrupts IAC membranes. Here we show that the recombinant Chaetomium thermophilum Atg15 lipase domain (CtAtg15(73-475)) possesses phospholipase activity that in acidic environments digests phospholipid to generate lysophospholipid and free fatty acid. The activity of CtAtg15(73-475) was markedly elevated by limited digestion with proteinase K. Proteinase K-treated CtAtg15(73-475) was detected as three fragments, with cleavage between S159 and V160, and between F209 and N210. We inserted the human rhinovirus 3C protease recognition sequence into the two sites and found that cleavage between S159 and V160 was important to activate CtAtg15(73-475). We confirmed that CtAtg15 compensated for the absence of ATG15 in Saccharomyces cerevisiae cells, indicating that CtAtg15 could disintegrate S. cerevisiae IAC in vivo. Further, both mitochondria and IAC were disintegrated by CtAtg15 in S. cerevisiae. This study suggests that Atg15 can degrade any organelle membrane, indicating that Atg15 plays a role in disrupting organelle membranes delivered to vacuoles by autophagy.