ubiquitin-conjugating enzyme Pex4p of Hansenula polymorpha is required for efficient functioning of the PTS1 import machinery

• Published in: The EMBO journal 1998-07, Vol.17 (13), p.3608-3618
• Main Authors: Klei, I.J. van der, Hilbrands, R.E, Kiel, J.A.K.W, Rasmussen, S.W, Cregg, J.M, Veenhuis, M
• Format: Article
• Language: English
• Subjects: amine oxidoreductases; Amino Acid Sequence; amino acid sequences; Biological Transport; cell membranes; enzymes; Fungal Proteins - genetics; Fungal Proteins - metabolism; genbank/af061604; Hansenula; immunocytochemistry; Intracellular Membranes - metabolism; Ligases - metabolism; malate synthase; Microbodies - metabolism; Molecular Sequence Data; Mutagenesis; mutants; nucleotide sequences; oxo-acid-lyases; peroxisomal targeting signal; peroxisome-deficient mutant; Peroxisome-Targeting Signal 1 Receptor; peroxisomes; pex4 gene; Pichia - enzymology; Pichia - genetics; protein amine oxidase; protein import; protein transport; proteins; PTS1 receptor; Receptors, Cytoplasmic and Nuclear - metabolism; Sequence Homology, Amino Acid; signal peptide; structural genes; Ubiquitins - metabolism; yeast
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/17.13.3608

We have cloned the Hansenula polymorpha PEX4 gene by functional complementation of a peroxisome‐deficient mutant. The PEX4 translation product, Pex4p, is a member of the ubiquitin‐conjugating enzyme family. In H.polymorpha , Pex4p is a constitutive, low abundance protein. Both the original mutant and the pex4 deletion strain (Δ pex4 ) showed a specific defect in import of peroxisomal matrix proteins containing a C‐terminal targeting signal (PTS1) and of malate synthase, whose targeting signal is not yet known. Import of the PTS2 protein amine oxidase and the insertion of the peroxisomal membrane proteins Pex3p and Pex14p was not disturbed in Δ pex4 cells. The PTS1 protein import defect in Δ pex4 cells could be suppressed by overproduction of the PTS1 receptor, Pex5p, in a dose–response related manner. In such cells, Pex5p is localized in the cytosol and in peroxisomes. The peroxisome‐bound Pex5p specifically accumulated at the inner surface of the peroxisomal membrane and thus differed from Pex5p in wild‐type peroxisomes, which is localized throughout the matrix. We hypothesize that in H.polymorpha Pex4p plays an essential role for normal functioning of Pex5p, possibly in mediating recycling of Pex5p from the peroxisome to the cytosol.