CAREER: Experimental and Computational Studies of Biomolecular Topology

非技术总结我们制造的每一样东西都是由原子或分子制成的。我们对原子和简单分子的行为有很好的了解，但更复杂的分子就更难理解了。一些更复杂的分子以简单分子不同的方式连接在一起。在简单的分子可能像乐高积木一样连接的地方，更复杂的分子可能像链子上的纽带一样连接。挑战在于分子非常小，太小了，用显微镜看不到，速度太快，不能用相机记录。我们通过两种方式克服了这一挑战。一种是使用更大的分子。DNA因含有我们的遗传密码而广为人知，但它也只是一个我们可以在显微镜下研究的极大分子。我们可以用DNA做实验来了解分子的行为，并将这些经验应用到更小的分子上。例如，我们测量单个DNA分子的弹性，并利用这些信息来了解组成橡胶的分子如何变得有弹性。另一种方法是使用计算机模拟，它可以向我们展示如果我们可以看到分子会如何行为。这个项目中研究的主要分子被称为动粒，它就像中世纪的链甲，由数千个相连的DNA环组成。我们用显微镜和计算机模拟来研究这些分子，以了解化学家们现在正在学习制造的链状分子会有多小。在未来，如果我们首先了解DNA链式邮件，我们对化学链式邮件分子的了解可能会允许更新、更精致的材料和纳米机器逐个原子地创造出来。我们还将教新一代学生研究分子，让他们拍摄充满分子的液滴蒸发时的微观视频。由于以前没有人观察到这些特定的分子以这种方式蒸发，除了学习如何做实验外，学生们还将学习发现新事物的感觉。作为这项资助的教育方面的一部分，少数族裔服务的主要本科院校的学生将进行原创性研究，作为基于课程的本科生研究体验的一部分。一项新发现的经历将在科学界建立一种归属感，并支持他们作为科学家而不仅仅是科学学生的身份。技术总结这个项目的目标是通过单分子实验和粗粒度模拟来了解复杂生物聚合物的分子拓扑和材料性质之间的关系。生物聚合物是微米尺度的介观体系，类似于纳米尺度的合成聚合物。这些实验将主要集中在单分子荧光显微镜上。运动体是由拓扑连接的DNA构成的平面网络，它将被作为合成聚戊二烯和热化石墨烯的模型系统进行研究。特别是，我们感兴趣的是THEN网络的拓扑结构，它可以通过酶的作用来调节，如何影响微流体剪切流中对动粒的弹性响应。我们还将开发一种方法，在活性液体中使用基因组长度的DNA作为示踪剂聚合物，通过化学能的转换来驱动它们自己的内部复杂流动。分子的涨落和构象将被用来确定类生命系统如何接近和避免最大熵态，从而建立帮助我们理解生命物理学的规则。此外，我们还将探索使用部分变性(线性DNA中的一种拓扑变化)来改进纳米孔基因组图谱技术。模拟将使用朗之万动力学和梯度优化来研究分子链的拓扑结构和它们形成的片层的大尺度结构之间的关系，以及变性转变和打结的分子拓扑之间的关系。作为这项资助的更广泛影响的一部分，一所少数族裔服务的主要本科院校的学生将进行原创性研究，作为基于课程的本科生研究经验的一部分，最初研究Marangoni流中的向列相液晶。一项新发现的经历将在科学界建立一种归属感，并支持他们作为科学家的身份，而不仅仅是科学学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON TECHNICAL SUMMARYEverything we make, we make out of atoms or molecules. We have a good understanding of how atoms and simple molecules behave, but it is harder to understand more complicated molecules. Some of the more complicated molecules are connected in ways that simpler molecules aren’t. Where simple molecules might connect like Lego bricks, more complicated molecules might connect like links on a chain. The challenge is that molecules are very small, too small to see with a microscope, and too fast to record with a camera. We overcome this challenge in two ways. One is by using bigger molecules. DNA is best known for containing our genetic code, but it’s also just an extremely large molecule that we can study in a microscope. We can do experiments with DNA to learn about how molecules behave, and apply those lessons to smaller molecules. For example, we measure how stretchy a single DNA molecule is, and use that information to understand how the molecules that make up rubber become stretchy. The other way is to use computer simulations, which can show us how molecules would behave if we could see them. The main molecules studied in this project are called kinetoplasts, which are like medieval chainmail armor made of thousands of connected loops of DNA. We study these with a microscope, and with computer simulations, to understand how much smaller chainmail-like molecules, which chemists are now learning to make, would behave. In the future, our understanding of chemical chainmail molecules could allow newer, fancier materials and nanomachines created atom by atom, if we first understand DNA chainmail. We will also teach a new generation of students to study molecules, by having them take microscopic videos of droplets full of molecules as they evaporate. Since nobody has observed those specific molecules evaporating in that way before, the students will learn what it’s like to discover something new, in addition to learning how to do the experiments. As part of the educational aspects of this grant, students at a minority-serving primarily-undergraduate institution will carry out original research as part of a course-based undergraduate research experience. The experience of a new discovery will build a sense of belonging in the scientific community and support their identities as scientists rather than just science students.TECHNICAL SUMMARYThe goal of this project is to understand the relationship between molecule topology and material properties of complex biopolymers through single-molecule experiments and coarse-grained simulations. Biopolymers serve as a mesoscopic system on the micron scale analogous to synthetic polymers on the nanometer scale. The experiments will largely focus on single-molecule fluorescence microscopy. Kinetoplasts, which are planar networks of topologically linked DNA, will be studied as a model system for synthetic polycatenanes and thermalized graphene. In particular, we are interested in how the topology of then network, which can be tuned by the action of enzymes, effects the elastic response to kinetoplasts in microfluidic shear flow. We will also develop assays to use genomic-length DNA as a tracer polymer in active fluids, which drive their own internal complex flows through the conversion of chemical energy. The fluctuations and conformations of the molecule will be used to determine how life-like systems approach and avoid maximum-entropy states, establishing rules that help us understand the physics of life. Additionally, we will explore the use of partial denaturation (a topological change in linear DNA) to improve nanopore genomic mapping technology. Simulations will use Langevin dynamics and gradient optimization to study the relationship between the topology of molecular chainmail and the large-scale structure of the sheets that they form, as well as to investigate the relationship between denaturation transitions and knotted molecular topologies. As part of the broader impacts of this grant, students at a minority-serving primarily-undergraduate institution will carry out original research as part of a course-based undergraduate research experience, initially studying nematic liquid crystals in Marangoni flow. The experience of a new discovery will build a sense of belonging in the scientific community and support their identities as scientists rather than just science students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.