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Calcium induced lateral phase separation triggers phospholipase D activity
S16
Abstracts / Chemistry and Physics of Lipids 149S (2007) S11–S22
References Cantor, R.S., 1997. Biochemistry 36, 2339–2344. Ollila, S., et al., 2007. J. Phys. Chem. B 111, 3139–3150. S. Ollila et al., J. Struct. Biol., in press. Niemela, P., et al., 2007. PLoS Comput. Biol. 3, 0304–0312. E. Terama et al., 2007, in preparation.
doi:10.1016/j.chemphyslip.2007.06.033 SO 11
Modeling of biological membranes in the study of natural polyphenol compounds
SO 12
Calcium induced lateral phase separation triggers phospholipase D activity Konstantin Kuppe 1 , Alfred Blume 2 , Renate Ulbrich-Hofmann 1 1 Institute
of Biochemistry and Biotechnology, Martin-Luther University Halle-Wittenberg, Germany; 2 Institute of Physical Chemistry, Martin-Luther University Halle-Wittenberg, Germany
Recent experimental studies have shown that natural polyphenols found in tea induce cell death in cancer cell lines. While the process by which these compounds interact with cancer cells remains unknown, it has been suggested that the binding of the polyphenols to the cell membrane is potentially part of the their effectiveness in selectively targeting cancer cells. We present here molecular dynamics simulations to model the interactions of bioactive molecules found in tea extract with lipid bilayers of biological membranes. Specifically, lipid bilayers are exposed to 10 different flavonoid molecules. To account for the composition effects of the lipid bilayer, a multi-component lipid bilayer is used as a model to a specific cancer cell, i.e., Hep2G cells (human liver cancer cells). The nature of the bilayer-flavonoid interactions may depend on many factors, such as the number of hydroxyl groups in the flavonoid, molecular size and presence of a galloyl moiety. Our results will provide insight into the experimental results and provide new details about the conformational changes of polyphenols near and on lipid bilayers as a means to understand their biological activity.
Plant ␣-type phospolipases D (PLD) are calcium dependent enzymes that catalyze the hydrolysis of the terminal phosphodiester bond of glycerophospholipids to release phosphatidic acid (PA) and the alcohol of the head group. While remodelling of membranes is assumed to be one of their cellular functions, the enzyme activity itself is regulated by the membrane structure and organization. Here we demonstrate that in the presence of calcium ions palmitoyl-2-oleoyl-sn-glycero3-phosphate (POPA) within 1-palmitoyl-2-oleoyl-snglycero-3-phosphocholine (POPC) vesicles stimulate the activity of recombinantly produced PLD (from white cabbage) up to 500-fold, whereas other negatively charged phospholipids do not show similar effects. Film balance measurements with PLD and non-hydrolysable 1,3-diacyl-glycero-phosphocholine monolayers containing increasing amounts of POPA revealed enhanced binding of PLD to the monolayer in the presence of PA. An activity assay utilizing a short-chain soluble substrate and POPA vesicles confirmed that an allosteric activation upon POPA binding cannot account for the extreme stimulation. To analyze the structure of POPC/POPA vesicles the thermotrophic phase behavior was studied by differential scanning calorimetry. Interestingly, lateral phase separation was observed in POPA containing vesicles on activating conditions. Therefore, we conclude that Ca2+ –POPA-complexes generate membrane microdomains facilitating the binding of PLD to the substrate and thereby causing increased enzyme activity.
doi:10.1016/j.chemphyslip.2007.06.034
doi:10.1016/j.chemphyslip.2007.06.035
Timothy Sirk 1 , Amadeu Sum 2 1 Mechanical Engineering Department, Virginia Tech, United States; 2 Chemical Engineering Department, Virginia Tech, United States
Abstracts / Chemistry and Physics of Lipids 149S (2007) S11–S22
References Cantor, R.S., 1997. Biochemistry 36, 2339–2344. Ollila, S., et al., 2007. J. Phys. Chem. B 111, 3139–3150. S. Ollila et al., J. Struct. Biol., in press. Niemela, P., et al., 2007. PLoS Comput. Biol. 3, 0304–0312. E. Terama et al., 2007, in preparation.
doi:10.1016/j.chemphyslip.2007.06.033 SO 11
Modeling of biological membranes in the study of natural polyphenol compounds
SO 12
Calcium induced lateral phase separation triggers phospholipase D activity Konstantin Kuppe 1 , Alfred Blume 2 , Renate Ulbrich-Hofmann 1 1 Institute
of Biochemistry and Biotechnology, Martin-Luther University Halle-Wittenberg, Germany; 2 Institute of Physical Chemistry, Martin-Luther University Halle-Wittenberg, Germany
Recent experimental studies have shown that natural polyphenols found in tea induce cell death in cancer cell lines. While the process by which these compounds interact with cancer cells remains unknown, it has been suggested that the binding of the polyphenols to the cell membrane is potentially part of the their effectiveness in selectively targeting cancer cells. We present here molecular dynamics simulations to model the interactions of bioactive molecules found in tea extract with lipid bilayers of biological membranes. Specifically, lipid bilayers are exposed to 10 different flavonoid molecules. To account for the composition effects of the lipid bilayer, a multi-component lipid bilayer is used as a model to a specific cancer cell, i.e., Hep2G cells (human liver cancer cells). The nature of the bilayer-flavonoid interactions may depend on many factors, such as the number of hydroxyl groups in the flavonoid, molecular size and presence of a galloyl moiety. Our results will provide insight into the experimental results and provide new details about the conformational changes of polyphenols near and on lipid bilayers as a means to understand their biological activity.
Plant ␣-type phospolipases D (PLD) are calcium dependent enzymes that catalyze the hydrolysis of the terminal phosphodiester bond of glycerophospholipids to release phosphatidic acid (PA) and the alcohol of the head group. While remodelling of membranes is assumed to be one of their cellular functions, the enzyme activity itself is regulated by the membrane structure and organization. Here we demonstrate that in the presence of calcium ions palmitoyl-2-oleoyl-sn-glycero3-phosphate (POPA) within 1-palmitoyl-2-oleoyl-snglycero-3-phosphocholine (POPC) vesicles stimulate the activity of recombinantly produced PLD (from white cabbage) up to 500-fold, whereas other negatively charged phospholipids do not show similar effects. Film balance measurements with PLD and non-hydrolysable 1,3-diacyl-glycero-phosphocholine monolayers containing increasing amounts of POPA revealed enhanced binding of PLD to the monolayer in the presence of PA. An activity assay utilizing a short-chain soluble substrate and POPA vesicles confirmed that an allosteric activation upon POPA binding cannot account for the extreme stimulation. To analyze the structure of POPC/POPA vesicles the thermotrophic phase behavior was studied by differential scanning calorimetry. Interestingly, lateral phase separation was observed in POPA containing vesicles on activating conditions. Therefore, we conclude that Ca2+ –POPA-complexes generate membrane microdomains facilitating the binding of PLD to the substrate and thereby causing increased enzyme activity.
doi:10.1016/j.chemphyslip.2007.06.034
doi:10.1016/j.chemphyslip.2007.06.035
Timothy Sirk 1 , Amadeu Sum 2 1 Mechanical Engineering Department, Virginia Tech, United States; 2 Chemical Engineering Department, Virginia Tech, United States