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

Abstract

Targeting of peroxisomal membrane proteins (PMPs) is a multistep process that requires not only recognition of PMPs in the cytosol but also their insertion into the peroxisomal membrane. As a consequence, targeting signals of PMPs (mPTS) are rather complex. A candidate protein for the PMP recognition event is Pex19p, which interacts with most PMPs. However, the respective Pex19p-binding sites are ill-defined and it is currently disputed whether these sites are contained within mPTS. By using synthetic peptide scans and yeast two-hybrid analyses, we determined and characterized Pex19p-binding sites in Pex11p and Pex13p, two PMPs from Saccharomyces cerevisiae. The sites turned out to be composed of a short helical motif with a minimal length of 11 amino acids. With the acquired data, it proved possible to predict and experimentally verify Pex19p-binding sites in several other PMPs by applying a pattern search and a prediction matrix. A peroxisomally targeted Pex13p fragment became mislocalized to the endoplasmic reticulum in the absence of its Pex19p-binding site. By adding the heterologous binding site of Pex11p, peroxisomal targeting of the Pex13p fragment was restored. We conclude that Pex19p-binding sites are well-defined entities that represent an essential part of the mPTS. INTRODUCTIONPeroxisomes are ubiquitous organelles of eukaryotic cells, whose proteins are imported posttranslationally. Matrix proteins are directed to peroxisomes by either of two targeting signals, a C-terminal PTS1 or an N-terminal PTS2. The topogenesis of peroxisomal membrane proteins (PMPs) is accomplished by yet another mechanism, because most of the peroxin mutants, characterized by their defect in the biogenesis of peroxisomes, exhibit a block in matrix protein import, but do import PMPs normally (Lazarow and Fujiki, 1985;Gould and Valle, 2000;Subramani et al., 2000;Purdue and Lazarow, 2001;Eckert and Erdmann, 2003). 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. Despite some differences, a picture emerged from these studies of a targeting signal consisting of one or more transmembrane domains in conjunction with a short sequence, which contains either a cluster of basic residues or a mixture of basic and hydrophobic amino acids (Dyer et al., 1996;Baerends et al., 2000b;Pause et al., 2000;...

Localization of mRNAs coding for peroxisomal proteins in the yeast, Saccharomyces cerevisiae

“…How peroxins target to peroxisomes is unclear, although several, such as Pex13 and Pex11, are targeted by binding to Pex19 and Pex3 (25). Yet a Pex13 mutant unable to bind Pex19 is imported into peroxisomes (26), suggesting the existence of multiple importation pathways.…”

Pex19p Binds Pex30p and Pex32p at Regions Required for Their Peroxisomal Localization but Separate from Their Peroxisomal Targeting Signals

“…Recently, a consensus sequence for recognition of a protein by Pex19p has been defined (21). Two putative Pex19p recognition sequences were identified in Pex30p at amino acids 24 -38 and 97-111 (Fig.…”

“…The direct insertion of PMPs into the peroxisomal membrane is facilitated by Pex19p, a peroxin that is localized predominantly to the cytosol and to a much lesser extent at the surface of peroxisomes (17)(18)(19). Pex19p interacts essentially with all PMPs via a consensus motif that is found at least once in a PMP (20,21). The interaction of Pex19p and a PMP could either prevent the aggregation of the PMP or serve to guide the PMP to the peroxisomal membrane.…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…Neurospora PEX3 enlists PEX19, a farnesylated cytosolic protein, to chaperone nascent PMPs to PEX3 for membrane insertion (Chen et al, 2014). Yeast PMPs bind PEX19 via a membrane peroxisome-targeting signal, a hydrophobic motif near the transmembrane domain (Rottensteiner et al, 2004); similar sequences are found in plant PMPs (Nyathi et al, 2012).…”