title: The peroxisomal protein import machinery displays a preference for monomeric substrates.
abstract: Peroxisomal matrix proteins are synthesized on cytosolic ribosomes and transported by the shuttling receptor PEX5 to the peroxisomal membrane docking/translocation machinery, where they are translocated into the organelle matrix. Under certain experimental conditions this protein import machinery has the remarkable capacity to accept already oligomerized proteins, a property that has heavily influenced current models on the mechanism of peroxisomal protein import. However, whether or not oligomeric proteins are really the best and most frequent clients of this machinery remain unclear. In this work, we present three lines of evidence suggesting that the peroxisomal import machinery displays a preference for monomeric proteins. First, in agreement with previous findings on catalase, we show that PEX5 binds newly synthesized (monomeric) acyl-CoA oxidase 1 (ACOX1) and urate oxidase (UOX), potently inhibiting their oligomerization. Second, in vitro import experiments suggest that monomeric ACOX1 and UOX are better peroxisomal import substrates than the corresponding oligomeric forms. Finally, we provide data strongly suggesting that although ACOX1 lacking a peroxisomal targeting signal can be imported into peroxisomes when co-expressed with ACOX1 containing its targeting signal, this import pathway is inefficient.
authors: Organelle Biogenesis and Function Group, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, Porto, Portugal.
authors: Marta O
authors: MO
authors: Freitas
authors: Organelle Biogenesis and Function Group, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, Porto, Portugal.
authors: Tânia
authors: T
authors: Francisco
authors: Organelle Biogenesis and Function Group, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, Porto, Portugal Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Porto, Portugal.
authors: Tony A
authors: TA
authors: Rodrigues
authors: Departement Cellulaire en Moleculaire Geneeskunde, KU Leuven-Universiteit Leuven, Leuven, Belgium.
authors: Celien
authors: C
authors: Lismont
authors: Departamento de Química, Universidade de Aveiro, Aveiro, Portugal.
authors: Pedro
authors: P
authors: Domingues
authors: Organelle Biogenesis and Function Group, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, Porto, Portugal.
authors: Manuel P
authors: MP
authors: Pinto
authors: Organelle Biogenesis and Function Group, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, Porto, Portugal.
authors: Cláudia P
authors: http://orcid.org/0000-0001-5197-2270
authors: CP
authors: Grou
authors: Departement Cellulaire en Moleculaire Geneeskunde, KU Leuven-Universiteit Leuven, Leuven, Belgium.
authors: Marc
authors: M
authors: Fransen
authors: Organelle Biogenesis and Function Group, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, Porto, Portugal Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Porto, Portugal jazevedo@ibmc.up.pt.
authors: Jorge E
authors: JE
authors: Azevedo
mesh_terms: D042962:Acyl-CoA Oxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002522:Chlorocebus aethiops; D003600:Cytosol / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D000074435:Peroxisome-Targeting Signal 1 Receptor; D020675:Peroxisomes / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D021381:Protein Transport; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014503:Urate Oxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: C000614264:PEX5 protein, human; D000074435:Peroxisome-Targeting Signal 1 Receptor; C000614265:Pex5 protein, mouse; D018160:Receptors, Cytoplasmic and Nuclear; D042962:Acyl-CoA Oxidase; D014503:Urate Oxidase
keywords: PEX5; acyl-CoA oxidase; docking/translocation machinery; peroxisomes; protein import; urate oxidase