A Cargo-centered Perspective on the PEX5 Receptor-mediated Peroxisomal Protein Import Pathway |
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Authors: | Tania Francisco Tony A. Rodrigues Marta O. Freitas Cláudia P. Grou Andreia F. Carvalho Clara Sá-Miranda Manuel P. Pinto Jorge E. Azevedo |
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Affiliation: | From the ‡Organelle Biogenesis and Function Group and ;the ¶Lysosome and Peroxisome Biology Unit, Instituto de Biologia Celular e Molecular (IBMC), Universidade do Porto, R. do Campo Alegre, 823, 4150-180 Porto and ;the §Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, R. de Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal |
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Abstract: | Peroxisomal matrix proteins are synthesized on cytosolic ribosomes and post-translationally targeted to the organelle by PEX5, the peroxisomal shuttling receptor. The pathway followed by PEX5 during this process is known with reasonable detail. After recognizing cargo proteins in the cytosol, the receptor interacts with the peroxisomal docking/translocation machinery, where it gets inserted; PEX5 is then monoubiquitinated, extracted back to the cytosol and, finally, deubiquitinated. However, despite this information, the exact step of this pathway where cargo proteins are translocated across the organelle membrane is still ill-defined. In this work, we used an in vitro import system to characterize the translocation mechanism of a matrix protein possessing a type 1 targeting signal. Our results suggest that translocation of proteins across the organelle membrane occurs downstream of a reversible docking step and upstream of the first cytosolic ATP-dependent step (i.e. before ubiquitination of PEX5), concomitantly with the insertion of the receptor into the docking/translocation machinery. |
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Keywords: | Peroxisomes Protein Sorting Protein Translocation Subcellular Organelles Ubiquitination PEX5 PTS1 Protein In Vitro Import Assays |
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