Yadav Indresh, Al Sulaiman Dana, Soh Beatrice W, Doyle Patrick S
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Institute of Materials Research and Engineering, 2 Fusionopolis Way, Singapore 138634, Singapore.
ACS Macro Lett. 2021 Nov 16;10(11):1429-1435. doi: 10.1021/acsmacrolett.1c00463. Epub 2021 Nov 3.
Conformational phase transitions of macromolecules are an important class of problems in fundamental polymer physics. While the conformational phase transitions of linear DNA have been extensively studied, this feature of topologically complex DNA remains unexplored. We report herein the polymer-and-salt-induced (Ψ) phase transition of 2D catenated DNA networks, called kinetoplasts, using single-molecule fluorescence microscopy. We observe that kinetoplasts can undergo a reversible transition from the flat phase to the collapsed phase in the presence of NaCl as a function of the crowding agent poly(ethylene glycol). The nature of this phase transition is tunable through varying ionic strengths. For linear DNA, the coexistence of coil and globule phases was attributed to a first order phase transition associated with a double well potential in the transition regime. Kinetoplasts, however, navigate from the flat to the collapsed phase by passing through an intermediate regime, characterized by the coexistence of a multipopulation with varying shapes and sizes. Conformations of individual molecules in the multipopulation are long-lived, which suggests a rugged energy landscape.
大分子的构象相变是基础聚合物物理学中的一类重要问题。虽然线性DNA的构象相变已得到广泛研究，但拓扑复杂DNA的这一特性仍未被探索。我们在此报告使用单分子荧光显微镜对二维连环DNA网络（称为动质体）的聚合物和盐诱导(Ψ)相变。我们观察到，在作为拥挤剂的聚乙二醇存在下，随着NaCl的加入，动质体可以经历从扁平相到塌陷相的可逆转变。这种相变的性质可以通过改变离子强度来调节。对于线性DNA，线圈相和球状体相的共存归因于与转变区域中的双阱势相关的一级相变。然而，动质体通过一个中间区域从扁平相转变为塌陷相，该中间区域的特征是存在多种形状和大小的群体共存。多群体中单个分子的构象是长期存在的，这表明存在崎岖的能量景观。
