Pex8p, an intraperoxisomal peroxin of Saccharomyces cerevisiae required for protein transport into peroxisomes binds the PTS1 receptor pex5p

We report the characterization of ScPex8p, which is essential for peroxisomal biogenesis in Saccharomyces cerevisiae. Cells lacking Pex8p are characterized by the presence of peroxisomal membrane ghosts and mislocalization of peroxisomal matrix proteins of the PTS1 and PTS2 variety to the cytosol. Pex8p is tightly associated with the lumenal face of the peroxisomal membrane. Consistent with its intraperoxisomal localization, Pex8p contains a peroxisomal targeting signal 1, and it interacts with the PTS1 receptor Pex5p. However, the Pex5p/Pex8p association is also observed upon deletion of the PTS1 of Pex8p, suggesting that Pex8p contains a second binding site for Pex5p. The pex8Delta mutant phenotype and the observed PTS1-independent interaction with the PTS1 receptor suggest that Pex8p is involved in protein import into the peroxisomal matrix. In pex8Delta cells, the PTS1 and PTS2 receptor still associate with membrane bound components of the protein import machinery, supporting the assumption that the Pex8p function in protein translocation follows the docking event.