Peroxisomes play a role in lipid metabolism. At least 25 human diseases affect the function or subcellular location of peroxisomal enzymes, or impair peroxisome biogenesis. The targeting of proteins to the peroxisomal matrix and membrane is mediated by peroxisomal targeting signals (PTSs), of which PTS1 and PTS2 allow import of proteins to the matrix, and the mPTS facilitates import to the membrane. Two key peroxins involved in matrix protein import, Pex5p and Pex7p, bind the PTS1 and PTS2 sequences, respectively, in the cytosol. The resulting cargo-receptor complexes dock with other peroxins on the peroxisomal membrane, before cargo translocation occurs into the organelle matrix. The different results obtained regarding the subcellular locations of Pex5p and Pex7p can be reconciled by the hypothesis that PTS receptors shuttle from the cytosol to the peroxisome matrix and then return to the cytosol during the import cycle. We have provided evidence, since the last submission, for this extended-shuttle model for human Pex5p (HsPex5p). Our proposed work focuses on the itineraries of Pex5p and Pex7p during the import cycle in human and yeast cells, and the mechanistic details of various steps of this shuttling cycle. Our studies will reveal the mechanism of action of these receptors, which are mutated in fatal disorders and are unique relative to signal-sequence receptors used by other organelles.
The aims are:1. What are the segments of HsPex5p that allow its import and export into and out of peroxisomes? Do different isoforms of HsPex5p shuttle? Are cargo binding or interactions of HsPex5p with the peroxisomal docking and translocation machinery necessary for its shuttling?2. Is the shuttling of Pex5p into and out of peroxisomes conserved in yeasts?3. What is the mechanism of steps in Pex5p shuttling such as transfer to the translocon, membrane translocation, cargo release and receptor export? We will also reconstitute receptor shuttling in vitro.4. What peroxins are necessary for the shuttling of Pex5p into and out of peroxisomes?5. Does Pex7p cycle into and out of the peroxisome matrix in yeast and in mammals? If so, what is the mechanism by which Pex7p shuttles?

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK059844-05
Application #
7105045
Study Section
Cell Development and Function Integrated Review Group (CDF)
Program Officer
Haft, Carol R
Project Start
2002-08-01
Project End
2007-07-31
Budget Start
2006-08-01
Budget End
2007-07-31
Support Year
5
Fiscal Year
2006
Total Cost
$286,374
Indirect Cost
Name
University of California San Diego
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
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Leon, Sebastien; Suriapranata, Ivet; Yan, Mingda et al. (2007) Characterization of protein-protein interactions: application to the understanding of peroxisome biogenesis. Methods Mol Biol 389:219-38
Farre, Jean-Claude; Shirahama-Noda, Kanae; Zhang, Lan et al. (2007) Localization of proteins and organelles using fluorescence microscopy. Methods Mol Biol 389:239-50
Zhang, Lan; Leon, Sebastien; Subramani, Suresh (2006) Two independent pathways traffic the intraperoxisomal peroxin PpPex8p into peroxisomes: mechanism and evolutionary implications. Mol Biol Cell 17:690-9
Leon, Sebastien; Zhang, Lan; McDonald, W Hayes et al. (2006) Dynamics of the peroxisomal import cycle of PpPex20p: ubiquitin-dependent localization and regulation. J Cell Biol 172:67-78