Insertion of the 70-kDa Peroxisomal Membrane Protein into Peroxisomal Membranes in Vivo and in Vitro

Peroxisomal ascorbate peroxidase (APX) is a carboxyl tail-anchored, type II (N cytosol -C matrix ) integral membrane protein that functions in the regeneration of NAD ؉ in glyoxysomes of germinated oilseeds and protection of peroxisomes in other organisms from toxic H 2 O 2 . Recently we showed that cottonseed peroxisomal APX was sorted post-translationally from the cytosol to peroxisomes via a novel reticular/circular membranous network that was interpreted to be a subdomain of the endoplasmic reticulum (ER), named peroxisomal ER (pER). Here we report on the molecular signals responsible for sorting peroxisomal APX. Deletions or site-specific substitutions of certain amino acid residues within the hydrophilic C-terminal-most eight-amino acid residues (includes a positively charged domain found in most peroxisomal integral membrane-destined proteins) abolished sorting of peroxisomal APX to peroxisomes via pER. However, the C-terminal tail was not sufficient for sorting chloramphenicol acetyltransferase to peroxisomes via pER, whereas the peptide plus most of the immediately adjacent 21-amino acid transmembrane domain (TMD) of peroxisomal APX was sufficient for sorting. Replacement of the peroxisomal APX TMD with an artificial TMD (devoid of putative sorting sequences) plus the peroxisomal APX C-terminal tail also sorted chloramphenicol acetyltransferase to peroxisomes via pER, indicating that the peroxisomal APX TMD does not possess essential sorting information. Instead, the TMD appears to confer the proper context required for the conserved positively charged domain to function within peroxisomal APX as an overlapping pER sorting signal and a membrane peroxisome targeting signal type 2.Peroxisomes are single membrane-bound organelles that do not contain DNA nor protein-synthesizing machinery. Data published thus far indicate that they acquire their nuclearencoded matrix and boundary membrane protein constituents from the cytosol in a regulated, post-translational manner. For instance, proteins destined for the peroxisomal matrix are sorted by at least two evolutionarily conserved targeting signals, the type 1 and type 2 peroxisomal targeting signal (PTS).

Section: Discussionmentioning

confidence: 99%

“…Data on the routing of PMPs directly to the peroxisomal boundary membrane has been derived mostly from in vitro studies (7)(8)(9)(10). Direct sorting of PMPs appears to be mediated by molecular chaperones and a two-step binding and insertion process that is temperature-dependent but does not require ATP hydrolysis.…”

mentioning

confidence: 99%

The Sorting Signals for Peroxisomal Membrane-bound Ascorbate Peroxidase Are within Its C-terminal Tail

Mullen

Trelease

2000

“…via the endoplasmic reticulum; see below). Thus, although there are no doubts that at least PMP22 and PMP70 are inserted into the peroxisomal membrane directly from the cytosol in liver cells (31,49), we reasoned that no assumptions should be made when studying the biogenesis pathway of a given PMP for the first time. These reservations are justified by recent data showing that some peroxisomal proteins reach the organelle membrane after traveling first through the endoplasmic reticulum (23, 50 -55).…”

Section: Discussionmentioning

confidence: 99%

The Import Competence of a Peroxisomal Membrane Protein Is Determined by Pex19p before the Docking Step

Pinto

Grou

Alencastre

et al. 2006

Biogenesis of the mammalian peroxisomal membrane requires the action of Pex3p and Pex16p, two proteins present in the organelle membrane, and Pex19p, a protein that displays a dual subcellular distribution (peroxisomal and cytosolic). Pex19p interacts with most peroxisomal intrinsic membrane proteins, but whether this property reflects its role as an import receptor for this class of proteins or a chaperone-like function in the assembly/disassembly of peroxisomal membrane proteins has been the subject of much controversy. Here, we describe an in vitro system particularly suited to address this issue. It is shown that insertion of a reporter protein into the peroxisomal membrane is a Pex3p-dependent process that does not require ATP/GTP hydrolysis. The system can be programmed with recombinant versions of Pex19p, allowing us to demonstrate that Pex19p-cargo protein complexes formed in the absence of peroxisomes are the substrates for the peroxisomal docking/ insertion machinery. Data suggesting that cargo-loaded Pex19p displays a much higher affinity for Pex3p than Pex19p alone are also provided. These results suggest that soluble Pex19p participates in the targeting of newly synthesized peroxisomal membrane proteins to the organelle membrane and support the existence of a cargo-induced peroxisomal targeting mechanism for Pex19p.

“…Preparation of the antibody against the COOH-terminal 15 amino acids of rat PMP70 is described in Ref. 30.…”

Section: Methodsmentioning

confidence: 99%

Identification of a Substrate-binding Site in a Peroxisomal β-Oxidation Enzyme by Photoaffinity Labeling with a Novel Palmitoyl Derivative

Kashiwayama

Tomohiro

Narita

et al. 2010

Self Cite

Peroxisomes play an essential role in a number of important metabolic pathways including ␤-oxidation of fatty acids and their derivatives. Therefore, peroxisomes possess various ␤-oxidation enzymes and specialized fatty acid transport systems. However, the molecular mechanisms of these proteins, especially in terms of substrate binding, are still unknown. In this study, to identify the substrate-binding sites of these proteins, we synthesized a photoreactive palmitic acid analogue bearing a diazirine moiety as a photophore, and performed photoaffinity labeling of purified rat liver peroxisomes. As a result, an 80-kDa peroxisomal protein was specifically labeled by the photoaffinity ligand, and the labeling efficiency competitively decreased in the presence of palmitoyl-CoA. Mass spectrometric analysis identified the 80-kDa protein as peroxisomal multifunctional enzyme type 2 (MFE2), one of the peroxisomal ␤-oxidation enzymes. Recombinant rat MFE2 was also labeled by the photoaffinity ligand, and mass spectrometric analysis revealed that a fragment of rat MFE2 (residues Trp 249 to Arg 251 ) was labeled by the ligand. MFE2 mutants bearing these residues, MFE2(W249A) and MFE2(R251A), exhibited decreased labeling efficiency. Furthermore, MFE2(W249G), which corresponds to one of the disease-causing mutations in human MFE2, also exhibited a decreased efficiency. Based on the crystal structure of rat MFE2, these residues are located on the top of a hydrophobic cavity leading to an active site of MFE2. These data suggest that MFE2 anchors its substrate around the region from Trp 249 to Arg 251 and positions the substrate along the hydrophobic cavity in the proper direction toward the catalytic center.Peroxisomes are organelles bound by a single membrane, which are present in almost all eukaryotic cells. Peroxisomes are involved in a variety of important metabolic processes including the ␤-oxidation of fatty acids, synthesis of plasmalogen, and bile acids (1). A specialized set of enzymes responsible for the peroxisomal functions are compartmentalized in the organelle, and the deficiency of peroxisomal enzymes causes severe metabolic disease such as acyl-CoA oxidase deficiency and D-bifunctional protein deficiency (2-4). Fibroblasts from patients with these deficiencies exhibit the disturbed peroxisomal ␤-oxidation of very long-chain fatty acids (VLCFAs), 4 and VLCFAs are accumulated in the plasma and tissues of these patients (5). Analyses of these peroxisomal diseases reflect the importance of the peroxisomal ␤-oxidation in organisms along with disclosing the enzymatic organization of the peroxisomal ␤-oxidation system. Peroxisomes are involved in the ␤-oxidation of VLCFAs, branched chain fatty acids such as pristanic acid, and bile acid intermediates such as dihydroxycholestanoic acid and trihydroxycholestanoic acid, which are incompatible with mitochondrial ␤-oxidation (6). Peroxisomal ␤-oxidation of fatty acids proceeds via a four-step pathway as in mitochondria, and multiple enzymes are involved in each step of the...