Characterization of Peroxisomal Pex5p from Rat Liver

Abstract

Pex5p is the receptor for the vast majority of peroxi- somal matrix proteins. Here, we show that about 15% of rat liver Pex5p is found in the peroxisomal fraction rep- resenting 0.06% of total peroxisomal protein. This pop- ulation of Pex5p displays all the characteristics of an intrinsic membrane protein. Protease protection assays indicate that this pool of Pex5p has domains exposed on both sides of the peroxisomal membrane. The strong interaction of Pex5p with the membrane of the organelle is not affected by mild protease treatment of intact or- ganelles, conditions that result in the partial degrada- tion of Pex13p. Cytosolic Pex5p is a monomeric protein. In contrast, virtually all peroxisomal Pex5p was found to be part of a stable 250-kDa protein assembly. This complex was isolated and shown to comprise just two subunits, Pex5p and Pex14p.