A conserved cysteine residue of Pichia pastoris Pex20p is essential for its recycling from the peroxisome to the cytosol.
We identified a cysteine residue, conserved near the N terminus of Pex5p- and Pex20p-like proteins, that is essential for the cytosolic relocation of peroxisomal Pex20p. Surprisingly, this residue is not completely essential for the function of the protein; its point mutation into a serine in Pex20p(C8S) causes the accumulation of the protein at the peroxisome membrane, but this is quickly followed by its subsequent degradation by an ubiquitin-dependent quality control pathway called RADAR (receptor accumulation and degradation in the absence of recycling). This degradative pathway allows partial growth of the Pex20p(C8S) mutant on peroxisome-requiring medium. Mutation of cysteine 8 (C8S) and lysine 19 (K19R), the target residue of the RADAR pathway within Pex20p, leads to a stable but non-functional protein because it fails to recycle to the cytosol. This suggests a role for Cys-8 in Pex20p recycling and that constitutive degradation of peroxisomal receptors can be a partially functional alternative to receptor recycling. In addition, expression of this mutant protein in wild-type cells confers a dominant-negative, oleate-specific growth defect, which is a useful tool for a better understanding of peroxisomal receptor recycling.
Léon
Sébastien
S
Section of Molecular Biology, Division of Biological Sciences, University of California, San Diego (UCSD), La Jolla, California 92093-0322, USA. leon@ijm.jussieu.fr
Subramani
Suresh
S
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D003545:Cysteine; D003600:Cytosol / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D020675:Peroxisomes / Q000378:metabolism*; D010843:Pichia / Q000737:chemistry*; D021381:Protein Transport; D025801:Ubiquitin / Q000378:metabolism
D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D025801:Ubiquitin; D003545:Cysteine