Saccharomyces cerevisiae Pex3p and Pex19p are required for proper localization and stability of peroxisomal membrane proteins

Abstract

The mechanisms by which peroxisomal membrane proteins (PMPs) are targeted to and inserted into membranes are unknown, as are the required components. We show that among a collection of 16 Saccharomyces cerevisiae peroxisome biogenesis (pex) mutants, two mutants, pex3Δ and pex19Δ, completely lack detectable peroxisomal membrane structures and mislocalize their PMPs to the cytosol where they are rapidly degraded. The other pexΔ mutants contain membrane structures that are properly inherited during vegetative growth and that house multiple PMPs. Even Pex15p requires Pex3p and Pex19p for localization to peroxisomal membranes. This PMP was previously hypothesized to travel via the endoplasmic reticulum (ER) to peroxisomes. We provide evidence that ER-accumulated Pex15p is not a sorting intermediate on its way to peroxisomes. Our results show that Pex3p and Pex19p are required for the proper localization of all PMPs tested, including Pex15p, whereas the other Pex proteins might only be required for targeting/import of matrix proteins.

Yarrowia lipolyticaCells Mutant for the Peroxisomal Peroxin Pex19p Contain Structures Resembling Wild-Type Peroxisomes

“…In this way, Pex19p would perform an important role in stabilizing the interaction between a putative membrane protein receptor and a PMP or the interactions of various proteins at the translocation/insertion step of a membrane protein at the peroxisomal membrane. Indeed, S. cerevisiae Pex19p has been shown to influence PMP stability (Hettema et al, 2000). A distribution for Pex19p that is partly cytosolic and partly peroxisomal has lent support to this idea.…”

“…Importantly, electron micrographs of Y. lipolytica pex19 cells reveal the presence of subcellular structures that closely resemble wild-type peroxisomes in regards to size, shape, electron density, and number. No such structures are observed in pex19 mutants of S. cerevisiae (Gö tte et al, 1998), and only small vesicular and tubular structures are found in P. pastoris pex19 mutants (Snyder et al, 1999a;Hettema et al, 2000). Isopycnic density gradient centrifugation also revealed the presence of vesicular structures in Y. lipolytica pex19 mutants, some of which were found to be of the same density as wild-type peroxisomes.…”

“…Pex19p has been shown to be primarily a cytosolic protein that can interact with a number of peroxisomal membrane proteins (Gö tte et al, 1998;Snyder et al, 1999aSnyder et al, , 1999bSnyder et al, , 2000Hettema et al, 2000;Sacksteder et al, 2000). Every ortholog of Pex19p contains a consensus sequence for the addition of a lipid farnesyl moiety at its extreme carboxy terminus (for a review of protein prenylation, see Omer and Gibbs, 1994), although the importance of this addition to the function of Pex19p is uncertain.…”

Autophagy and Related processes in Trypanosomatids: Insights from Genomic and Bioinformatic Analyses

“…39 The apparent absence of PEX3 reflects a likely case of gene displacement. This is a key factor for the formation of membrane-associated complexes for import of proteins into the peroxisomal matrix 40,41 but must be removed, by mechanisms as yet unknown, before peroxisomes can be degraded in H. polymorpha. 42 Since its apparent absence was so surprising, additional searches were carried out focusing on identified conserved motifs 41 but no trypanosomatid homologues could be identified.…”

Peroxisomal Membrane Proteins Contain Common Pex19p-binding Sites that Are an Integral Part of Their Targeting Signals

“…To date, only three peroxins with a potential role in PMP targeting have been identified, namely Pex3p (Hettema et al, 2000;South et al, 2000), Pex16p in mammals (South and Gould, 1999;Honsho et al, 2002), and Pex19p (Gö tte et al, 1998;Matsuzono et al, 1999;Snyder et al, 1999;Soukupova et al, 1999). In cells lacking any of these proteins, PMPs are either degraded or mistargeted to other subcellular compartments such as mitochondria, the endoplasmic reticulum (ER) and membranes of unknown origin (Ghaedi et al, 2000;Hettema et al, 2000;Sacksteder et al, 2000).In accordance with a distinct pathway, PMPs use neither PTS1 nor PTS2. The targeting signals of PMPs (mPTS) that direct and insert PMPs into the peroxisomal membrane have been determined for a number of PMPs of several species.…”