The Matrix Protein Import Complex in Yeast

Nearly all peroxisomal matrix proteins contain specific peroxisomal targeting signals (PTS1 or PTS2) that are posttranslationally recognized and bound in the cytosol by soluble import receptors. Whereas the PTS1 receptor Pex5p targets its cargo autonomously to the peroxisomal membrane, the PTS2-receptor Pex7p requires auxiliary proteins, so-called co-receptors. Docking of receptor–cargo complexes at the peroxisomal membrane is facilitated by a membrane subcomplex consisting of Pex13p, Pex14p, and Pex17p. Pex5p together with its docking partner Pex14p forms a transient pore in the peroxisomal membrane, which allows the translocation of folded and even oligomerized PTS1 proteins. After release of the matrix enzymes into the peroxisomal lumen, the PTS receptors are dislocated from the membrane to the cytosol and thus made available for the next import cycle. In this review, we will report most recent advances in understanding the formation and function of receptor complexes in the cytosol and at the peroxisomal membrane.