title: Autophagy delivers misfolded secretory proteins accumulated in endoplasmic reticulum to vacuoles in the filamentous fungus Aspergillus oryzae.
abstract: Autophagy is a conserved intracellular degradation process of eukaryotic cells. In filamentous fungi, although autophagy has been reported to have multiple physiological roles, it is not clear whether autophagy is involved in the degradation of misfolded proteins. Here, we investigated the role of autophagy in the degradation of misfolded secretory proteins accumulated in endoplasmic reticulum (ER) in the filamentous fungus Aspergillus oryzae. In late-phase cultures, a disulfide bond-deleted mutant of the secretory protein α-amylase AmyB fused with mDsRed that had accumulated in the ER was subsequently delivered to vacuoles, whereas wild-type AmyB-mDsRed was predominantly located at cell walls and septa. To examine the involvement of autophagy in the delivery of mutant AmyB to vacuoles, mutant AmyB-EGFP was expressed in an A. oryzae autophagy-deficient strain (ΔAoatg8). Microscopic examination revealed that the protein delivery to vacuoles did not occur in the absence of autophagic activity, with mutant AmyB-mDsRed forming large spherical structures surrounded by ER membrane. Hence, we conclude that autophagy is responsible for the delivery of misfolded secretory proteins accumulated in the ER to vacuoles for degradation during late-growth phase in A. oryzae. This is the first study to provide evidence that autophagy plays a role in the degradation of misfolded secretory proteins in filamentous fungi.
authors.affiliation: Department of Biotechnology, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Kimura
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Maruyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Kikuma
authors.forename: Manabu
authors.initials: M
authors.lastname: Arioka
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kitamoto
mesh_terms: D001236:Aspergillus oryzae / Q000201:enzymology*; D001343:Autophagy; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D021381:Protein Transport; D014617:Vacuoles / Q000201:enzymology*; D001614:beta-Amylase / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D001614:beta-Amylase