Evidence has accumulated that the voltage dependent anion channel (VDAC), located on the outer membrane of mitochondria, plays a central role in apoptosis. The involvement of VDAC oligomerization in apoptosis has been suggested in various studies. However, it still remains unknown how exactly VDAC supra-molecular assembly can be regulated in the membrane. Previous studies suggested the possible influence of various proteins on the formation of VDAC oligomers, but the important issue of the VDAC oligomeric state regulation by lipids has not been studied so far. Nevertheless, the effect of lipids on the oligomerization of several membrane proteins has been mentioned in the literature and in general, protein-lipid interactions are under extensive investigation.
In the present work, I addressed the influence of lipids on VDAC oligomerization experimentally by reconstituting the fluorescently labelled VDAC in giant unilamellar vesicles (GUVs)—a chemically well defined, cell-free minimal model system. Fluorescence cross-correlation spectroscopy was performed to determine the oligomeric state of VDAC. I investigated the effect of important for apoptosis anionic lipids, phosphatidylglycerol and cardiolipin, on VDAC oligomerization. I demonstrated that phosphatidylglycerol significantly enhances VDAC oligomerization in the membrane, whereas cardiolipin disrupts VDAC oligomers. These results suggest that up- or down- regulation of these lipids in mitochondria during apoptosis can tune VDAC oligomerization in the membrane.
Thus, this study sheds light on the role played by the above-mentioned lipids in the regulation of VDAC oligomerization during apoptosis and provides additional information on the molecular mechanisms of the programmed cell death.
Another objective of this work was to investigate the partitioning of VDAC into liquid disordered or liquid ordered lipid phases. The existence of lipid domains or the lipid rafts in mitochondria and VDAC enrichment in these rafts is still under debate. Additionally, mitochondrial VDAC was recently found in the plasma membrane. The role of this VDAC is not known, however, it was shown to be located in caveolae (specialized lipid rafts) and play an important role in neuronal apotosis and Alzheimer’s disease. Therefore, VDAC partitioning to the lipid rafts is an interesting question for investigation.
The possibility to reconstitute VDAC into minimal model systems–GUVs with phase separation, allowed to reveal the preferential partitioning of VDAC into liquid disordered lipid domain, which suggests either non-raft localization of VDAC or the requirement of the other factors for the recruitment of VDAC into lipid rafts.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:25958 |
| Date | 12 March 2012 |
| Creators | Betaneli, Viktoria |
| Contributors | Schwille, Petra, Eng, Lukas, Ravens, Ursula, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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