Disease relevance of PEX7

• We investigated the molecular dysfunction of Pex7p variants in mammals, including Pex7p-W221ter and Pex7p with one site mutation at G217R, A218V, or L292ter, which frequently occurs in the human fatal genetic peroxisomal disease rhizomelic chondrodysplasia punctata, showing a cell phenotype of PTS2 import defect [1].
• Our observation that Pas7p also interacts with the human peroxisomal thiolase suggests that in the human peroxisomal disorders characterized by an import defect for PTS2 proteins (classical rhizomelic chondrodysplasia punctata), a functional homologue of Pas7p may be impaired [2].

High impact information on PEX7

• We have previously isolated a Saccharomyces cerevisiae peroxisomal biogenesis mutant, pex7 (formerly peb1/pas7), which demonstrates a striking similarity to the cellular phenotype of RCDP fibroblasts in that PTS1 targeting is functional, but the peroxisomal packaging of PTS2 targeted thiolase is lacking [3].
• Two cytosolic import receptors, Pex5p and Pex7p, along with approximately 12 membrane-bound peroxins participate in this process [4].
• Pex7p translocates in and out of peroxisomes in Saccharomyces cerevisiae [5].
• The reexported Pex7p is functional, resulting in import of thiolase into peroxisomes and improved growth of the yeast on oleic acid [5].
• Cleavage of the link between Pex7p and GFP within peroxisomes liberates GFP, which remains inside the organelle, and Pex7p, which exits to the cytosol [5].

Biological context of PEX7

• Mutation in ZPG207 PEX7 was determined by reverse transcription PCR; a G-to-A transition caused a 1-amino acid substitution, W221ter [1].
• The latter binding site at the C terminus of ScPex14p overlaps with a binding site of Pex7p at amino acid residues 235-325 [6].
• A Myc epitope-tagged Pas7p, expressed under the control of the CUP1 promotor, was functionally active [7].
• Thus, Pas7p appears to be essential for protein translocation into peroxisomes as well as formation of the lumen of the organelle [8].
• Point mutations that alter conserved residues of the C3HC4 motif abolish PAS7 activity and reduce zinc binding, suggesting that Pas7p binds zinc in vivo and that zinc binding is essential for PAS7 function [8].

Anatomical context of PEX7

• Subsequently, the formed Pex7p/cargo complex is transported from the cytosol to the peroxisomal docking complex, consisting of Pex13p and Pex14p [9].
• Subcellular fractionation and protease protection studies demonstrated bimodal distribution of Pex7p between the cytoplasm and peroxisomes in CHO and human cells [1].
• We suggest that Pas7p mediates the binding of thiolase to these organelles [7].
• Interference between the PHA-4 and PEB-1 transcription factors in formation of the Caenorhabditis elegans pharynx [10].
• Here we describe the novel factor PEB-1, which is coexpressed with PHA-4 in many pharyngeal cell types, including muscles, epithelial cells, marginal cells, and glands, but is undetectable in the pharyngeal nervous system [11].

Associations of PEX7 with chemical compounds

• Thus the NH2-terminal 56-amino acid residues of Peb1p are necessary and sufficient for peroxisomal targeting [12].
• We have cloned PAS7 by complementation of the oleic acid non-utilizing phenotype of the pas7-1 strain [7].

Physical interactions of PEX7

• We also found that the cytosolic Pex7p/thiolase-containing complex includes Pex18p [9].

Other interactions of PEX7

• Pex18p and Pex21p also interacted with this region, albeit only in the presence of Pex7p [9].
• Here we mapped the Pex7p interaction domain of Pex13p to its N-terminal 100 amino acids [9].
• Yeast Pex14p possesses two functionally distinct Pex5p and one Pex7p binding sites [6].
• Peb1 is a peroxisome biogenesis mutant isolated in Saccharomyces cerevisiae that is selectively defective in the import of thiolase into peroxisomes but has a normal ability to package catalase, luciferase and acyl-CoA oxidase (Zhang, J. W., C. Luckey, and P. B. Lazarow. 1993. Mol. Biol. Cell. 4:1351-1359) [12].
• In pex8Delta cells, the PTS1 and PTS2 receptor still associate with membrane bound components of the protein import machinery, supporting the assumption that the Pex8p function in protein translocation follows the docking event [13].

Analytical, diagnostic and therapeutic context of PEX7

• Finally, a thiolase-Peb1p complex was isolated by immunoprecipitation [12].
• With the two-hybrid assay, we observed a strong interaction between Peb1p and thiolase that was abolished by deleting the first 16 amino acids of thiolase [12].
• In addition, using a combination of several independent approaches (two-hybrid system, co-immunoprecipitation, affinity chromatography and high copy suppression), we show that Pas7p specifically interacts with thiolase in vivo and in vitro [2].
• Peb1p was tagged with hemagglutinin epitopes and determined to be exclusively within peroxisomes by digitonin permeabilization, immunofluorescence, protease protection and immuno-electron microscopy (Zhang, J. W., and P. B. Lazarow. 1995. J. Cell Biol. 129:65-80) [12].
• Electrophoretic mobility-shift assays provide no evidence for the formation of a PHA-4/PEB-1 complex in vitro but rather show that PHA-4 and PEB-1 cannot bind C183 simultaneously [10].

References