吸附在一帶正電脂膜平面上之DNA分子形態與動力學

本論文中，作者利用螢光顯微技術，直接觀察單一DNA分子吸附在一帶正電的脂膜平面上之形態改變。以螢光顯微鏡進行觀察，DNA分子剛吸附在脂膜上時呈現近似圓形的形狀，而隨著時間演進，DNA分子在脂膜上的大小及其形態之不對稱性會逐漸增加。透過使用不同帶電量的脂膜，我們發現，雖然單一DNA分子在吸附過程中的形態改變具有很大的變異性，但是，這些DNA分子的平均大小隨著時間演進的增長，在不同帶電量的脂膜上，皆可以運用一個指數函數予以描述。此指數函數顯示了DNA分子在吸附過程中形態改變的主要時間尺度：即DNA分子在帶電量較高的脂膜上改變形態所需的時間較長。藉由進一步觀察單一DNA分子的吸附過程，我們發現DNA分子的形態改變，與脂膜的帶電量有關：在帶電量較高的脂膜上的DNA分子是藉由許多不對稱的「突出」(extrusions) 來擴張；但在帶電量較低的脂膜上的擴張形式則類似一逐漸擴大的圓盤。此一差異顯示了DNA分子與脂膜間複雜的交互作用。此外，藉由追蹤DNA分子在吸附過程中的質心位置，我們亦發現 DNA 分子的方均位移(mean square displacement)亦可作為形態改變的指標。

關鍵字

吸附；巨分子；顯微技術；單分子；螢光；細胞膜；生物物理；表面改質；介面；動力學；結構；脂膜；高分子；去氧核醣核酸

並列摘要

Relaxation of the chain-like DNA molecules upon adsorption on a supported cationic lipid membrane is time-resolved by direct imaging. Following the stochastic landing onto the membrane at a nearly spherical initial state, these DNA coils gradually relax and expand their apparent size in a highly anisotropic fashion. By using membranes with different charge densities, we show that the time evolution of the ensemble-averaged apparent size of the DNA molecules can be characterized by a generic exponential function despite significant variation between individual events. The exponential fitting also determines the primary time scale in the relaxation process, which is faster for DNA adsorbed on membranes with lower charge density. Examination on the conformational change of single DNA molecules on different membranes reveals non-trivial interaction between the adsorbed DNA molecule and the host membrane, with DNA relaxing through more anisotropic extrusions on membranes with higher charge density. The ensemble-averaged square displacement of the center-of-mass of the DNA molecules, which are found to be rescaled by the primary time scale, can be another indicator of the relaxation process.

並列關鍵字

polymer ； DNA ； adsorption ； biomolecule ； plasma membrane ； cell membrane ； lipid membrane ； interface ； dynamics ； structure ； surface modification ； biophysics ； single molecule ； flurorescence microscopy

參考文獻

[1] A. Xie and S. Granick, “Phospholipid membranes as substrates for polymer adsorp-tion,” NATURE MATERIALS, vol. 1, pp. 129–133, OCT 2002.

[2] C. Saﬁnya, “Structures of lipid-DNA complexes: supramolecular assembly and gene delivery,” CURRENT OPINION IN STRUCTURAL BIOLOGY, vol. 11, pp. 440–448, AUG 2001.

[3] K. Ewert, A. Ahmad, H. Evans, and C. Saﬁnya, “Cationic lipid-DNA complexes for non-viral gene therapy: relating supramolecular structures to cellular pathways,” EXPERT OPINION ON BIOLOGICAL THERAPY, vol. 5, pp. 33–53, JAN 2005

[5] P.-G. de Gennes, Scaling Concepts in Polymer Physcis. Cornell University Press, 1979.

[6] T. Odijk, “On the statistics and dynamics of conﬁned or entangled stiﬀ polymers,” Macromolecules, vol. 16, pp. 1340–1344, 1983.

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吸附在一帶正電脂膜平面上之DNA分子形態與動力學

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