Pex15p is a phosphorylated, tail-anchored type II (N_cyt-C_lumen) integral peroxisomal membrane protein required for peroxisome biogenesis (1). Pex15p is the first peroxin shown to be posttranslationally modified, but the importance of this phosphorylation for Pex15p function in peroxisome biogenesis is not yet understood (2). Cells lacking Pex15p are characterized by the mislocalization of peroxisomal matrix proteins to the cytosol, while peroxisomal membrane proteins are still targeted to peroxisomal remnants. Overexpression of Pex15p results in impaired peroxisome assembly, and causes a profound proliferation of endomembranes which contain Pex15p as well as at least one other peroxisomal membrane marker (1).

From the continuity of the proliferated membranes with the nuclear envelope, it has been suggested that they most likely originate from the endoplasmic reticulum (ER) (1), but definitive proof of the ER origin of these membranes has not yet been obtained (2). In this respect, the observed O-glycoslylation of overexpressed Pex15p indicates that its carboxy-terminal tail protrudes into ER membranes (1). Further, a Pex15p-invertase fusion protein was shown to be N-glycosylated, even when expressed at the endogenous protein level. From these results, it appears that the association of Pex15p with ER membranes is more likely to reflect a normal step in its topogenesis than an artificial mislocalization caused by its overexpression (2). Thus, Pex15p may be targeted to peroxisomes via the ER, or to both peroxisomes and the ER (1).

Last updated: 2005-03-08