LCST-Type Polymer Behavior of Single-Stranded DNA: From Fundamentals to Switchable Block Copolymers and Chemically Fueled, Transient Polymerization-Induced Self-Assembly

• Applicant: Professor Dr. Andreas Walther
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 466493239

Building on our recent discovery (Nature Nanotechnology 13, 730 (2018)) of the sequence-specific phase-segregation of ssDNA – a polymer property of ssDNA – it is the central scientific objective of this proposal to understand and tune the phase-segregation behavior of purine-rich ssDNA and activate this polymer property of ssDNA for the design of self-assembling systems, including colloidal coacervates and block copolymer (BCP) structures. The investigations are directed towards merging the fields of BCP science known from synthetic polymers and DNA nanoscience with its highly developed strand displacement reactions, aptamer technologies, and possibilities for enzymatic manipulations with a mission to cross fertilize approaches and implement the best of two worlds into new systems. A decisive aspect is also to step outside equilibrium and investigate chemically fueled and transient polymerization induced self-assembly, where structures can be autonomously built and destroyed using antagonistic enzymes. First, we will aim for a quantitative understanding on the sequence dependence of the phase-segregation of ssDNA and then identify pathways for isothermal liquid/liquid phase-separation in response to distinct chemical signals, in particular using strand displacement reactions with controlled kinetics, as well as ATP using aptamers.Second, by controlling the ssDNA cloud points and kinetics of phase-segregation using sequence coding, we will aim for uniform coacervate droplets using controlled nucleation and growth processes. Third, we will design and synthesize ssDNA-b-(synthetic polymer) BCPs with very long ssDNA (co)polymers, as well as with encoded sequences for molecular recognition capability for aptamers and strand displacement reactions. Based upon those, we will study thermally and isothermally triggered formation of BCP-type self-assemblies, yet, in striking contrast to previous work, the ssDNA block will be the solvophobic block. Fourth, by merging the understanding of the first three parts, we will design polymerization-induced self-assembly pro-cesses (PISA) by living enzymatic polymerization of phase-segregating ssDNA blocks (under phase-segregation condi-tions) and, moreover, we will evolve this approach to make transient PISA structures by adding exonuclease 1 that is able to degrade the formed ssDNA with a time delay. The project will introduce distinct advantages of DNA nanoscience approaches into polymer phase-segregation and self-assembly, and will also introduce new polymer chemistry and polymer science tools to DNA self-assembly. In a more abstract fashion, we hope to be able to inspire biologists to think about the importance of ssDNA phase-segregation in the nucleus and subcellular condensate context, and potentially provide new tools to study fundamental biological processes using soft matter approaches.

• DFG Programme: Research Grants