title: Autophagosome targeting and membrane curvature sensing by Barkor/Atg14(L).
abstract: The class III phosphatidylinositol 3-kinase (PI3KC3) is crucial for autophagosome biogenesis. It has been long speculated to nucleate the autophagosome membrane, but the biochemical mechanism of such nucleation activity remains unsolved. We recently identified Barkor/Atg14(L) as the targeting factor for PI3KC3 to autophagosome membrane. Here, we show that we have characterized the region of Barkor/Atg14(L) required for autophagosome targeting and identified the BATS [Barkor/Atg14(L) autophagosome targeting sequence] domain at the carboxyl terminus of Barkor. Bioinformatics and mutagenesis analyses revealed that the BATS domain binds to autophagosome membrane via the hydrophobic surface of an intrinsic amphipathic alpha helix. BATS puncta overlap with Atg16 and LC3, and partially with DFCP1, in a stress-inducible manner. Ectopically expressed BATS accumulates on highly curved tubules that likely represent intermediate autophagic structures. PI3KC3 recruitment and autophagy stimulation by Barkor/Atg14(L) require the BATS domain. Furthermore, our biochemical analyses indicate that the BATS domain directly binds to the membrane, and it favors membrane composed of phosphatidylinositol 3-phosphate [PtdIns(3)P] and phosphatidylinositol 4,5-biphosphate [PtdIns(4,5)P2]. By binding preferentially to curved membranes incorporated with PtdIns(3)P but not PtdIns(4,5)P2, the BATS domain is capable of sensing membrane curvature. Thus, we propose a novel model of PI3KC3 autophagosome membrane nucleation in which its autophagosome-specific adaptor, Barkor, accumulates on highly curved PtdIns(3)P enriched autophagic membrane via its BATS domain to sense and maintain membrane curvature.
authors.affiliation: Division of Biochemistry and Molecular Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
authors.forename: Weiliang
authors.initials: W
authors.lastname: Fan
authors.forename: Ashley
authors.initials: A
authors.lastname: Nassiri
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhong
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001343:Autophagy / Q000502:physiology*; D000071183:Autophagy-Related Proteins; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007425:Intracellular Membranes / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D010588:Phagosomes / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000145:classification / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: C539000:ATG14 protein, human; D033942:Adaptor Proteins, Vesicular Transport; D000071183:Autophagy-Related Proteins; D017931:DNA Primers; D018129:Phosphatidylinositol Phosphates; D011993:Recombinant Fusion Proteins; C055525:phosphatidylinositol 3-phosphate; D019869:Phosphatidylinositol 3-Kinases