PAMAM6树枝状聚合物和DNA：小角X射线散射揭示的pH依赖性“串珠”行为
PAMAM6 dendrimers and DNA: pH dependent "beads-on-a-string" behavior revealed by small angle X-ray scattering
摘要：
DNA与聚阳离子的相互作用不仅对我们理解染色质致密化很重要，而且对表征参与转录、复制和修复的DNA结合蛋白也很重要。已知DNA形成几种类型的液晶相，这取决于聚阳离子结构和电荷密度等因素。理论研究和模拟已经预测了DNA包裹在带正电荷的球形聚阳离子周围。作为组蛋白八聚体或其他DNA包装蛋白的潜在模拟物，聚（酰胺基胺）6代（PAMAM 6）树枝状聚合物已被选择用于我们的研究。用小角X射线散射（SAXS）研究了PAMAM 6诱导的DNA自组装，揭示了组装体的结构对环境pH值和树枝状聚合物浓度的依赖性。我们表明，在pH值8.5的致密相的形成和特征在于由一个2D-柱状六方晶格转化成一个3D的六方晶格与树枝状聚合物浓度增加（电荷比N/P）。此外，从稀释的样品在pH 8.5和5.5收集的散射数据的系统分析，使我们提出了一个包装方案的DNA周围PAMAM 6在pH 5.5。
英文摘要：
DNA interactions with polycations are not only important for our understanding of chromatin compaction but also for characterizing DNA-binding proteins involved in transcription, replication and repair. DNA is known to form several types of liquid-crystalline phases depending, among other factors, on polycation structure and charge density. Theoretical studies and simulations have predicted the wrapping of DNA around spherical positively charged polycations. As a potential mimic of the histone octamer or other DNA wrapping proteins, poly(amido amine) generation 6 (PAMAM6) dendrimers have been chosen for our study. The self-assembly of DNA induced by PAMAM6 has been investigated using small angle X-ray scattering (SAXS) in order to reveal the assemblies' structure dependence on the pH of the environment and on dendrimers concentration. We demonstrate that at pH 8.5 dense phases are formed and characterized by a 2D-columnar hexagonal lattice which is transformed into a 3D hexagonal lattice with increasing dendrimer concentration (charge ratio N/P). Moreover, a systematic analysis of the scattering data collected from diluted samples at pH 8.5 and 5.5 have led us to propose a wrapping scenario of DNA around PAMAM6 at pH 5.5.
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