title: Proteomic analysis reveals that the Rab GTPase RabE1c is involved in the degradation of the peroxisomal protein receptor PEX7 (peroxin 7).
abstract: The biogenesis of peroxisomes is mediated by peroxins (PEXs). PEX7 is a cytosolic receptor that imports peroxisomal targeting signal type 2 (PTS2)-containing proteins. Although PEX7 is important for protein transport, the mechanisms that mediate its function are unknown. In this study, we performed proteomic analysis to identify PEX7-binding proteins using transgenic Arabidopsis expressing green fluorescent protein (GFP)-tagged PEX7. Our analysis identified RabE1c, a small GTPase, as a PEX7 binding partner. In vivo analysis revealed that GTP-bound RabE1c binds to PEX7 and that a subset of RabE1c localizes to peroxisomes and interacts with PEX7 on the peroxisome membrane. Unlike endogenous PEX7, which is predominantly localized to the cytosol, GFP-PEX7 accumulates abnormally on the peroxisomal membrane and induces degradation of endogenous PEX7, concomitant with a reduction in import of PTS2-containing proteins and decreased peroxisomal β-oxidation activity. Thus, GFP-PEX7 on the peroxisomal membrane exerts a dominant negative effect. Mutation of RabE1c restored endogenous PEX7 protein expression and import of PTS2-containing proteins as well as peroxisomal β-oxidation activity. Treatment with proteasome inhibitors also restored endogenous PEX7 protein levels in GFP-PEX7-expressing seedlings. Based on these findings, we conclude that RabE1c binds PEX7 and facilitates PEX7 degradation in the presence of immobile GFP-PEX7 accumulated at the membrane.
authors.affiliation: Department of Cell Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan.
authors.forename: Songkui
authors.initials: S
authors.lastname: Cui
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Fukao
authors.forename: Shoji
authors.initials: S
authors.lastname: Mano
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamada
authors.forename: Makoto
authors.initials: M
authors.lastname: Hayashi
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D005799:Genes, Dominant; D013058:Mass Spectrometry / Q000379:methods; D018613:Microscopy, Confocal / Q000379:methods; D008954:Models, Biological; D008957:Models, Genetic; D010455:Peptides / Q000737:chemistry; D000074437:Peroxisomal Targeting Signal 2 Receptor; D020675:Peroxisomes / Q000378:metabolism; D021381:Protein Transport; D040901:Proteomics / Q000379:methods; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; C000614267:PEX7 protein, Arabidopsis; D010455:Peptides; D000074437:Peroxisomal Targeting Signal 2 Receptor; D018160:Receptors, Cytoplasmic and Nuclear; C580661:AT3G46060 protein, Arabidopsis; D020691:rab GTP-Binding Proteins