Yeast and mammalian autophagosomes exhibit distinct phosphatidylinositol 3-phosphate asymmetries.
Phosphatidylinositol 3-kinase is indispensable for autophagy but it is not well understood how its product, phosphatidylinositol 3-phosphate (PtdIns(3)P), participates in the biogenesis of autophagic membranes. Here, by using quick-freezing and freeze-fracture replica labelling, which enables determination of the nanoscale distributions of membrane lipids, we show that PtdIns(3)P in yeast autophagosomes is more abundant in the luminal leaflet (the leaflet facing the closed space between the outer and inner autophagosomal membranes) than in the cytoplasmic leaflet. This distribution is drastically different from that of the mammalian autophagosome in which PtdIns(3)P is confined to the cytoplasmic leaflet. In mutant yeast lacking two cytoplasmic phosphatases, ymr1Δ and sjl3Δ, PtdIns(3)P in the autophagosome is equally abundant in the two membrane leaflets, suggesting that the PtdIns(3)P asymmetry in wild-type yeast is generated by unilateral hydrolysis. The observed differences in PtdIns(3)P distribution suggest that autophagy in yeast and mammals may involve substantially different processes.
1] Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550, Japan [2].
Jinglei
J
Cheng
1] Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550, Japan [2].
Akikazu
A
Fujita
Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
Hayashi
H
Yamamoto
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550, Japan.
Tsuyako
T
Tatematsu
Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
Soichiro
S
Kakuta
Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
Keisuke
K
Obara
Frontier Research Center, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
Yoshinori
Y
Ohsumi
Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa-ku, Nagoya 466-8550, Japan.
Toyoshi
T
Fujimoto
D001343:Autophagy; D005614:Freeze Fracturing; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D013194:Staining and Labeling / Q000379:methods*
D018129:Phosphatidylinositol Phosphates; C055525:phosphatidylinositol 3-phosphate; D010744:Phosphoric Monoester Hydrolases; C061816:phosphatidylinositol-3-phosphatase