Cis1/Atg31 is required for autophagosome formation in Saccharomyces cerevisiae

Autophagy is the bulk degradation of cytosolic materials in lysosomes/vacuoles of eukaryotic cells. In the yeast Saccharomyces cerevisiae, 17 Atg proteins are known to be involved in autophagosome formation. Genome wide analyses have shown that Atg17 interacts with numerous proteins. Further studies on these interacting proteins may provide further insights into membrane dynamics during autophagy. Here, we identify Cis1/Atg31 as a protein that exhibits similar phenotypes to Atg17. ATG31 null cells were defective in autophagy and lost viability under starvation conditions. Localization of Atg31 to pre-autophagosomal structures (PAS) was dependent on Atg17. Coimmunoprecipitation experiments indicated that Atg31 interacts with Atg17. Together, Atg31 is a novel protein that, in concert with Atg17, is required for proper autophagosome formation.     

Atg15 in Saccharomyces cerevisiae consists of two functionally distinct domains

Autophagy is a cellular degradation system widely conserved among eukaryotes. During autophagy, cytoplasmic materials fated for degradation are compartmentalized in double membrane–bound organelles called autophagosomes. After fusing with the vacuole, their inner membrane–bound structures are released into the vacuolar lumen to become autophagic bodies and eventually degraded by vacuolar hydrolases. Atg15 is a lipase that is essential for disintegration of autophagic body membranes and has a transmembrane domain at the N-terminus and a lipase domain at the C-terminus. However, the roles of the two domains in vivo are not well understood. In this study, we found that the N-terminal domain alone can travel to the vacuole via the multivesicular body pathway, and that targeting of the C-terminal lipase domain to the vacuole is required for degradation of autophagic bodies. Moreover, we found that the C-terminal domain could disintegrate autophagic bodies when it was transported to the vacuole via the Pho8 pathway instead of the multivesicular body pathway. Finally, we identified H435 as one of the residues composing the putative catalytic triad and W466 as an important residue for degradation of autophagic bodies. This study may provide a clue to how the C-terminal lipase domain recognizes autophagic bodies to degrade them.     

Changes in Sulfhydryl Groups and Hydrodynamic Behavior of Thiolated Polyvinyl Alcohol Reacted with Oxidized Lipid

A synthetic polymer, thiolated polyvinyl alcohol (SH-PVA), was used for examining the reaction between sulfhydryls and lipids during dough mixing. When SH-PVA was incubated with linoleic acid hydroperoxide at a concentration of 1/12 to 1/4 mole to a mole of SH group, progressive oxidation of sulfhydryl was observed and a part of disulfides seemed to be further oxidized in some cases. The hydrodynamic behavior of SH-PVA treated with oxidized linoleic acid was similar to that of SH-PVA treated with an oxidizing agent, potassium bromate; non-Newtonian flow and increase in viscosity were observed. The peak of the gel filtration pattern of SH-PVA shifted to a faster elution position upon treatment with oxidized linoleic acid. These results probably indicate the formation of an interchain disulfide linkage. In view of these results, we discussed the role of lipids involved in oxidation of free SH groups in the rheological properties of gluten and dough.