Protein Modification and Turnover
Monroe-Augustus, Melanie , Lingard, Matthew J. , Bartel, Bonnie .
A role for peroxins in peroxisome associated protein degradation.
Peroxins are encoded by PEX genes and function in peroxisome biogenesis, maintenance, and matrix protein import. All peroxisomes characteristically house certain reactions, such as fatty acid beta-oxidation. In addition, peroxisomes can be specialized to carry out different functions during plant development. For example, glyoxysomes are specialized peroxisomes found in seedlings and senescing tissues that contain glyoxylate cycle enzymes, whereas leaf-type peroxisomes lack glyoxylate cycle enzymes and contain photorespiration enzymes. During seedling development, glyoxysomes are remodeled into leaf peroxisomes, and obsolete glyoxysomal proteins are eliminated. The mechanism of this peroxisomal matrix protein degradation is unknown. We observed that isocitrate lyase (ICL) and malate synthase, two glyoxylate cycle enzymes that normally function only early in seedling development, persist in certain pex mutants, including pex4 and pex6, after the proteins have disappeared in wild-type seedlings. Preliminary fractionation results reveal that the stabilized ICL in pex4 and pex6 remains associated with peroxisomes. These mutants display severe sucrose dependence during germination, reflecting reduced rates of seed storage fatty acid catabolism, but appear to import matrix proteins normally, whereas other peroxin mutants with slight sucrose dependence show severe defects in matrix protein import. These paradoxical phenotypes suggest that a subset of peroxins, including PEX4 and PEX6, may work both in their established capacity for receptor recycling during matrix protein import and in an additional type of peroxisomal retrotranslocation: the removal of matrix proteins that are damaged or no longer needed.
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1 - Rice University, Biochemistry and Cell Biology, 6100 S. Main MS-140, Houston, Tx, 77005, United States
2 - Rice University, Biochemistry and Cell Biology
peroxisomal matrix protein import
peroxisomal matrix protein degradation
Presentation Type: ASPB Minisymposium
Location: International Ballroom South/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:55 AM