Identification and Characterization of the Human Orthologue of Yeast Pex14p

Abstract

Pex14p is a central component of the peroxisomal protein import machinery, which has been suggested to provide the point of convergence for PTS1- and PTS2-dependent protein import in yeast cells. Here we describe the identification of a human peroxisome-associated protein (HsPex14p) which shows significant similarity to the yeast Pex14p. HsPex14p is a carbonate-resistant peroxisomal membrane protein with its C terminus exposed to the cytosol. The N terminus of the protein is not accessible to exogenously added antibodies or protease and thus might protrude into the peroxisomal lumen. HsPex14p overexpression leads to the decoration of tubular structures and mislocalization of peroxisomal catalase to the cytosol. HsPex14p binds the cytosolic receptor for the peroxisomal targeting signal 1 (PTS1), a result consistent with a function as a membrane receptor in peroxisomal protein import. Homo-oligomerization of HsPex14p or interaction of the protein with the PTS2-receptor or HsPex13p was not observed. This distinguishes the human Pex14p from its counterpart in yeast cells and thus supports recent data suggesting that not all aspects of peroxisomal protein import are conserved between yeasts and humans. The role of HsPex14p in mammalian peroxisome biogenesis makes HsPEX14 a candidate PBD gene for being responsible for an unrecognized complementation group of human peroxisome biogenesis disorders.

ACKNOWLEDGMENTS

We are grateful to Stephen Gould, Wilhelm Just, and Wolfgang Schliebs for kindly providing antibodies and plasmids. We are indebted to Ulrike Freimann, Uta Ricken, and Sigrid Wüthrich for technical assistance. We thank Peter Rehling and Michael Schwierskott for reading of the manuscript.

G. K. Will was supported by a fellowship from the Graduiertenkolleg der Ruhr-Universität Bochum. G. Dodt was supported by a Lise Meitner fellowship from NRW. This work was supported by grants from the Deutsche Forschungsgemeinschaft (Er178/2-1, Ku329/17-3, and SFB480) and by the Fond der Chemischen Industrie.

ADDENDUM IN PROOF

While this paper was in review, Fransen et al. (Proc. Natl. Acad. Sci. USA 95:8087–8092, 1998) reported that HsPex14p interacts with Pex5p and Pex13p (SH3) and is directly required for peroxisomal protein import.