title: Redox-regulated cargo binding and release by the peroxisomal targeting signal receptor, Pex5.
abstract: In its role as a mobile receptor for peroxisomal matrix cargo containing a peroxisomal targeting signal called PTS1, the protein Pex5 shuttles between the cytosol and the peroxisome lumen. Pex5 binds PTS1 proteins in the cytosol via its C-terminal tetratricopeptide domains and delivers them to the peroxisome lumen, where the receptor·cargo complex dissociates. The cargo-free receptor is exported to the cytosol for another round of import. How cargo release and receptor recycling are regulated is poorly understood. We found that Pex5 functions as a dimer/oligomer and that its protein interactions with itself (homo-oligomeric) and with Pex8 (hetero-oligomeric) control the binding and release of cargo proteins. These interactions are controlled by a redox-sensitive amino acid, cysteine 10 of Pex5, which is essential for the formation of disulfide bond-linked Pex5 forms, for high affinity cargo binding, and for receptor recycling. Disulfide bond-linked Pex5 showed the highest affinity for PTS1 cargo. Upon reduction of the disulfide bond by dithiothreitol, Pex5 transitioned to a noncovalent dimer, concomitant with the partial release of PTS1 cargo. Additionally, dissipation of the redox balance between the cytosol and the peroxisome lumen caused an import defect. A hetero-oligomeric interaction between the N-terminal domain (amino acids 1-110) of Pex5 and a conserved motif at the C terminus of Pex8 further facilitates cargo release, but only under reducing conditions. This interaction is also important for the release of PTS1 proteins. We suggest a redox-regulated model for Pex5 function during the peroxisomal matrix protein import cycle.
authors.affiliation: Section of Molecular Biology, Division of Biological Sciences, University California, San Diego, La Jolla, California 92093-0322.
authors.forename: Changle
authors.initials: C
authors.lastname: Ma
authors.affiliation: Section of Molecular Biology, Division of Biological Sciences, University California, San Diego, La Jolla, California 92093-0322.
authors.forename: Danielle
authors.initials: D
authors.lastname: Hagstrom
authors.affiliation: Section of Molecular Biology, Division of Biological Sciences, University California, San Diego, La Jolla, California 92093-0322.
authors.forename: Soumi Guha
authors.initials: SG
authors.lastname: Polley
authors.affiliation: Section of Molecular Biology, Division of Biological Sciences, University California, San Diego, La Jolla, California 92093-0322. Electronic address: ssubramani@ucsd.edu.
authors.forename: Suresh
authors.initials: S
authors.lastname: Subramani
mesh_terms: D020816:Amino Acid Motifs; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D000074435:Peroxisome-Targeting Signal 1 Receptor; D020675:Peroxisomes / Q000235:genetics / Q000378:metabolism*; D010843:Pichia / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; C000614263:PEX5 protein, Pichia pastoris; D000074435:Peroxisome-Targeting Signal 1 Receptor; D018160:Receptors, Cytoplasmic and Nuclear
keywords: Disulfide Bonding; PTS1 Receptor; Peroxisomes; Pichia pastoris; Protein Translocation; Receptor Recycling; Redox Regulation; Yeast
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