Zhang Ce, Shao Pei Ge, van Kan Jeroen A, van der Maarel Johan R C
Biophysics and Complex Fluids Group and Centre for Ion Beam Applications, Department of Physics, National University of Singapore, 2 Science Drive 3, Republic of Singapore.
Proc Natl Acad Sci U S A. 2009 Sep 29;106(39):16651-6. doi: 10.1073/pnas.0904741106. Epub 2009 Sep 16.
The effect of dextran nanoparticles on the conformation and compaction of single DNA molecules confined in a nanochannel was investigated with fluorescence microscopy. It was observed that the DNA molecules elongate and eventually condense into a compact form with increasing volume fraction of the crowding agent. Under crowded conditions, the channel diameter is effectively reduced, which is interpreted in terms of depletion in DNA segment density in the interfacial region next to the channel wall. Confinement in a nanochannel also facilitates compaction with a neutral crowding agent at low ionic strength. The threshold volume fraction for condensation is proportional to the size of the nanoparticle, due to depletion induced attraction between DNA segments. We found that the effect of crowding is not only related to the colligative properties of the agent and that confinement is also important. It is the interplay between anisotropic confinement and osmotic pressure which gives the elongated conformation and the possibility for condensation at low ionic strength.
利用荧光显微镜研究了葡聚糖纳米颗粒对限制在纳米通道中的单个DNA分子构象和压缩的影响。观察到随着拥挤剂体积分数的增加，DNA分子伸长并最终凝聚成紧密形式。在拥挤条件下，通道直径有效减小，这可根据通道壁附近界面区域中DNA片段密度的耗尽来解释。在低离子强度下，纳米通道中的限制也有利于与中性拥挤剂的压缩。由于DNA片段之间的耗尽诱导吸引力，凝聚的阈值体积分数与纳米颗粒的大小成正比。我们发现拥挤效应不仅与试剂的依数性有关，而且限制也很重要。各向异性限制和渗透压之间的相互作用赋予了伸长的构象以及在低离子强度下凝聚的可能性。
