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Typus
KomplettPlagiat
Bearbeiter
Klgn
Gesichtet
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Untersuchte Arbeit:
Seite: 37, Zeilen: 1 ff. (entire page)
Quelle: Anézo 2003
Seite(n): 60, 61, Zeilen: 60:16ff; 61:1ff
[The fluid character of the physiologically relevant fluid crystalline phase makes experimental studies particularly difficult and only limited atomic-level data from X-ray or neutron] diffraction have been for long accessible, compared with the amount of data available on proteins and nucleic acids. As structures from X-ray crystallography are usually taken as starting configurations for MD calculations, the difficulty in obtaining such data for lipid bilayers may have slowed down the development of the MD technique in the biomembrane field. Another reason may be the difficulty in developing force fields able to reproduce the dynamic properties of lipid molecules. Since the fluidity of lipid bilayers determines to a great extent their structural and functional properties, reliable computer models have to include the flexible nature of the lipid molecules, static models being unrealistic. The occurrence of complex hydrophilic and hydrophobic interactions within membranes also poses formidable modeling challenges. For all these reasons, simulations of lipid membranes have attracted in the past far less attention than the molecular modeling of small molecules and proteins. More recently, however, with the increasing computational capacities and the awareness of the biological importance of membranes, the modeling of lipid bilayers has emerged as a growing research field [22].

In order to begin to understand membrane properties, simple model systems have first been investigated. The earliest studies of lipid systems appeared in the literature in the 1980’s. Monolayer [25] and bilayer [26] membrane simulations were performed on simplified models, in which the lipid headgroups and/or hydrocarbon tails were stylized and the solvent disregarded. The application of MD simulations to lipid bilayers with explicit solvent was pioneered by Egberts and Berendsen in 1988 [27]. They proceeded to an all-atom simulation of a system consisting of a mixture of water, soap (sodium decanoate), and alcohol (decanol). Such ternary systems form stable multilamellar phases and provide good models for the study of the general behavior of lipid membranes, although they often exhibit denser packing and a higher ordering degree than phospholipid membranes. Egberts published in a PhD-thesis in 1988 [28] and in an article in 1994 [29] the first simulation of a phospholipid-water bilayer system in full atomic detail. In 1992 and 1993, several research groups reported simulation studies of single component membranes consisting, for instance, of dipalmitoylphosphatidylcholine (DPPC), dilauroylphosphatidylethanolamine (DLPE), or palmitoyloleoylphosphatidylcholine (POPC) molecules, demonstrating that the MD [technique applied to patches of a few phospholipids in water has enormous potential and can give detailed insights into lipid motions and interactions.]


22. Wiese, M. Computer Simulations of Phospholipids and Drug-Phospholipid Interactions. In Drug - Membrane Interactions; Seydel, J. K., Wiese, M., Eds.; Wiley - VCH Verlag: Weinheim, 2002.

25. Kox, A. J.; Michaels, J. P. J.; Wiegel, F. W. Nature 1980, 287, 317.

26. van der Ploeg, P.; Berendsen, H. J. C. J. Chem. Phys. 1982, 76, 3271.

27. Egberts, E.; Berendsen, H. J. C. J. Chem. Phys. 1988, 89 , 3718.

28. Egberts, E. Molecular Dynamics Simulations of Multibilayer Membranes. Ph. D. Thesis, University of Groningen, The Netherlands, 1988.

29. Egberts, E.; Marrink, S. J.; Berendsen, H. J. C. Eur. Biophys. J. with Biophys. Lett. 1994, 22, 423.

[page 60]

The fluid character of the physiologically relevant fluid crystalline phase makes experimental studies particularly difficult and only limited atomic-level data from X-ray or neutron diffraction have been for long accessible, compared with the amount of data available on proteins and nucleic acids. As structures from X-ray crystallography are usually taken as starting configurations for MD calculations, the difficulty in obtaining such data for lipid bilayers may have slowed down the development of the MD technique in the biomembrane field. Another reason may be the difficulty in developing force fields able to reproduce the dynamic properties of lipid molecules. Since the fluidity of lipid bilayers determines to a great extent their structural and functional properties, reliable computer models have to include the flexible nature of the lipid molecules, static models being unrealistic. The occurrence of complex hydrophilic and hydrophobic interactions within membranes also poses formidable modeling challenges. For all these reasons, simulations of lipid membranes have attracted in the past far less attention than the molecular modeling of small molecules and proteins. More recently, however, with the increasing computational capacities and the awareness of the biological importance of membranes, the modeling of lipid bilayers has emerged as a growing research field [44].

[page 61]

In order to begin to understand membrane properties, simple model systems have first been investigated. The earliest studies of lipid systems appeared in the literature in the 1980’s. Monolayer [52] and bilayer [53] membrane simulations were performed on simplified models, in which the lipid headgroups and/or hydrocarbon tails were stylized and the solvent disregarded. The application of MD simulations to lipid bilayers with explicit solvent was pioneered by Egberts and Berendsen in 1988 [54]. They proceeded to an all-atom simulation of a system consisting of a mixture of water, soap (sodium decanoate), and alcohol (decanol). Such ternary systems form stable multilamellar phases and provide good models for the study of the general behavior of lipid membranes, although they often exhibit a denser packing and a higher ordering degree than phospholipid membranes. Egberts published in a PhD-thesis in 1988 [55] and in an article in 1994 [56] the first simulation of a phospholipid-water bilayer system in full atomic detail. In 1992 and 1993, several research groups reported simulation studies of single component membranes consisting, for instance, of dipalmitoylphosphatidylcholine (DPPC), dilauroylphosphatidylethanolamine (DLPE), or palmitoyloleoylphosphatidylcholine (POPC) molecules, demonstrating that the MD technique applied to patches of a few phospholipids in water has enormous potential and can give detailed insights into lipid motions and interactions.


[44] M. Wiese. Computer Simulation of Phospholipids and Drug-Phospholipid Interactions. In: Drug-Membrane Interactions. J. K. Seydel and M. Wiese (Eds.), Wiley-VCH Verlag GmbH, Weinheim, 2002.

[52] A. J. Kox, J. P. J. Michels, and F. W. Wiegel. Nature, 287:317–319, 1980.

[53] P. van der Ploeg and H. J. C. Berendsen. J. Chem. Phys., 76:3271–3276, 1982.

[54] E. Egberts and H. J. C. Berendsen. J. Chem. Phys., 89:3718–3732, 1988.

[55] E. Egberts. Molecular Dynamics Simulations of Multibilayer Membranes. Ph. D. thesis, University of Groningen, The Netherlands, 1988.

[56] E. Egberts, S. J. Marrink, and H. J. C. Berendsen. Eur. Biophys. J. with Biophys. Lett., 22:423–436, 1994.

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