Yarrowia lipolytica Pex20p, Saccharomyces cerevisiae Pex18p/Pex21p and mammalian Pex5pL fulfil a common function in the early steps of the peroxisomal PTS2 import pathway.

Import of peroxisomal matrix proteins is essential for peroxisome biogenesis. Genetic and biochemical studies using a variety of different model systems have led to the discovery of 23 PEX genes required for this process. Although it is generally believed that, in contrast to mitochondria and chloroplasts, translocation of proteins into peroxisomes involves a receptor cycle, there are reported differences of an evolutionary conservation of this cycle either with respect to the components or the steps involved in different organisms. We show here that the early steps of protein import into peroxisomes exhibit a greater similarity than was thought previously to be the case. Pex20p of Yarrowia lipolytica, Pex18p and Pex21p of Saccharomyces cerevisiae and mammalian Pex5pL fulfil a common function in the PTS2 pathway of their respective organisms. These non-orthologous proteins possess a conserved sequence region that most likely represents a common PTS2-receptor binding site and di-aromatic pentapeptide motifs that could be involved in binding of the putative docking proteins. We propose that not necessarily the same proteins but functional modules of them are conserved in the early steps of peroxisomal protein import.