| Research Abstract |
Peroxisome is a ubiquitous organelle, present in almost all types of eukaryotic cells from yeast to humans. It carries out important metabolic functions including fatty acid degradation and other oxidative reactions. More than twenty peroxisome assembly gene (PEX genes) have been identified, and human peroxisome biogenesis disorders (PBDs) due to the PEX gene deficiencies are known. In the present work, we studied the mechanism of peroxisome biogenesis, employing the fibroblasts of PBD patients and peroxisome-defective CHO cell lines. The results are :
(1) We cloned several new PEX genes.
(2) We identified casual genes for several complementation groups of PBDs, and detected the responsible mutations.
(3) Cases of different severity are often found in the same complementation groups of PBDs. For several complementation groups of PBDs, fibroblasts from the patients of milder forms of PBDs exhibited a temperature-sensitive phenotype, that is, catalase-containing peroxisomes were recovered at lower temperatures. A causal point mutation was identified in a patient. Fibroblasts form these patients have "catalase-less peroxisomes" that contain fatty acid β-oxidation enzymes but not catalase, which seemed to be the cause of the milder phenotype.
(4) Many peroxisome-deficient cells contain peroxisome-related membrane structures lacking the peroxisome matrix proteins, called "ghosts". It was shown by genetic complementation of the PEX2- and PEX5-defective cells, that peroxisomes were recovered by the transport of matrix proteins to the pre-existing ghosts. In the mutant cells defective of PEX6, a gene coding for an AAA-ATPase, peroxisome matrix proteins were found to be accumulated in membrane structures closely contacting with, but different from, the ghosts, suggesting an abnormality in the membrane assembly processes.
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