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 biogenesi s. Genetic and biochemical studies using a variety of different model syste ms have led to the discovery of 23 PEX genes required for this process. Alt hough it is generally believed that, in contrast to mitochondria and chloro plasts, translocation of proteins into peroxisomes involves a receptor cycl e, there are reported differences of an evolutionary conservation of this c ycle either with respect to the components or the steps involved in differe nt organisms. We show here that the early steps of protein import into pero xisomes exhibit a greater similarity than was thought previously to be the case. Pex20p of Yarrowia lipolytica, Pex18p and Pex21p of Saccharomyces cer evisiae and mammalian Pex5pL fulfil a common function in the PTS2 pathway o f their respective organisms. These non-orthologous proteins possess a cons erved sequence region that most likely represents a common PTS2-receptor bi nding site and di-aromatic pentapeptide motifs that could be involved in bi nding of the putative docking proteins. We propose that not necessarily the same proteins but functional modules of them are conserved in the early st eps of peroxisomal protein import.