Molecular Dissection of the Organization and the Dynamics of Intracellular Lipid Domains

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I. Involvement of mitochondrial cardiolipin domains in apoptosis.Cytochrome c is a proapoptotic factor that binds preferentially to cardiolipin (CL), a mitochondrial lipid, but not to cardiolipin hydroperoxide (Cl-OOH). Our studies using overexpression of mitochondrial phospholipid hydroperoxide glutathione peroxidase (PHGPx) suggests that the generation of CL-OOH in mitochondria might be a primary event that triggers the release of cytochrome c.II. Characterization of lysobisphosphatidic acid domain in late endosomes.Late endosomes accumulates internal membranes within the lumen of the organelle. These intemal membranes are enriched in the specific lipid, Iysobisphosphatidic acid (LBPA). Using LBPA-specific monoclonal antibody and fluorescence correlation spectroscopy, we have determined that LBPA domain is exclusively localized in the lumen of late endosomes.III. Caveolae and glycosylphosphatidylinositol domain.Most mammalian cells have in their membrane at least two types of lipid m … More icrodomains, non-invaginated lipid rafts and caveolae. Glycosylphosphatidylinositol (GPI)-anchored proteins constitute a class of proteins that are enriched in rafts but not caveolae at steady state. By using GPI-deficient cells and the cells overexpressing caveolin-1, we showed there is an inverse correlation between the expression of GPI-anchored proteins and caveolin-1.IV. Sphingomyelin-specific proteinLysenin is a novel 4lkDa sphingomyelin-binding protein obtained from coelomic fluid of the earthworrn Eisenia foetida. We have developed recombinant lysenin and examined the distribution of sphingomyelin under electron microscope. Sphingomyelin was accumulated in caveolae in endothelial cells. Sphingomyelin was also distributed in endosomes and the trans-Golgi network but excluded from the Golgi cistemae. We also examined sphingomyelin in Niemann-Pick type A (NPA) fibroblpsts, which accumulate sphingomyelin intracellularly Sphingomyelin is accumuiated in late endosomes lysosomes in NPA. Interestingly, other lipid raft components such as ganglioside GM1, and cholesterol were aiso accumulated in the same organelle. Our results suggest that re-distribution of lipid raft occurs in NPA. Less