title: Peroxisome degradation by microautophagy in Pichia pastoris: identification of specific steps and morphological intermediates.
abstract: We used the dye N-(3-triethylammoniumpropyl)-4-(p-diethylaminophenylhexatrienyl ) pyridinium dibromide (FM4-64) and a fusion protein, consisting of the green fluorescent protein appended to the peroxisomal targeting signal, Ser-Lys-Leu (SKL), to label the vacuolar membrane and the peroxisomal matrix, respectively, in living Pichia pastoris cells and followed by fluorescence microscopy the morphological and kinetic intermediates in the vacuolar degradation of peroxisomes by microautophagy and macroautophagy. Structures corresponding to the intermediates were also identified by electron microscopy. The kinetics of appearance and disappearance of these intermediates is consistent with a precursor-product relationship between intermediates, which form the basis of a model for microautophagy. Inhibitors affecting different steps of microautophagy did not impair peroxisome delivery to the vacuole via macroautophagy, although inhibition of vacuolar proteases affected the final vacuolar degradation of green fluorescent protein (S65T mutant version [GFP])-SKL via both autophagic pathways. P. pastoris mutants defective in peroxisome microautophagy (pag mutants) were isolated and characterized for the presence or absence of the intermediates. These mutants, comprising 6 complementation groups, support the model for microautophagy. Our studies indicate that the microautophagic degradation of peroxisomes proceeds via specific intermediates, whose generation and/or processing is controlled by PAG gene products, and shed light on the poorly understood phenomenon of peroxisome homeostasis.
authors.affiliation: Department of Biology, University of California, San Diego, La Jolla, California 92093-0322, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Sakai
authors.forename: A
authors.initials: A
authors.lastname: Koller
authors.forename: L K
authors.initials: LK
authors.lastname: Rangell
authors.forename: G A
authors.initials: GA
authors.lastname: Keller
authors.forename: S
authors.initials: S
authors.lastname: Subramani
mesh_terms: D000222:Adaptation, Physiological; D000730:Androstadienes / Q000494:pharmacology; D001343:Autophagy / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology; D005456:Fluorescent Dyes; D049452:Green Fluorescent Proteins; D007425:Intracellular Membranes; D007700:Kinetics; D008164:Luminescent Proteins; D008830:Microbodies / Q000378:metabolism*; D010446:Peptide Fragments; D010664:Phenylmethylsulfonyl Fluoride / Q000494:pharmacology; D010843:Pichia / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011480:Protease Inhibitors / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D013194:Staining and Labeling; D014617:Vacuoles; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; C092350:FM 4-64; D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D010446:Peptide Fragments; D011480:Protease Inhibitors; D011500:Protein Synthesis Inhibitors; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D049452:Green Fluorescent Proteins; D000431:Ethanol; D010664:Phenylmethylsulfonyl Fluoride; D003513:Cycloheximide; D000077191:Wortmannin