Reversible Supra-Folding of User-Programmed Functional DNA Nanostructures on Fuzzy Cationic Substrates.

We report that user-defined DNA nanostructures, such as two-dimensional (2D) origamis and nanogrids, undergo a rapid higher-order folding transition, referred to as supra-folding, into three-dimensional (3D) compact structures (origamis) or well-defined µm-long ribbons (nanogrids), when they adsorb on a soft cationic substrate prepared by layer-by-layer deposition of polyelectrolytes. Once supra-folded, origamis can be switched back on the surface into their 2D original shape through addition of heparin, a highly charged anionic polyelectrolyte known as an efficient competitor of DNA-polyelectrolyte complexation. Orthogonal to DNA base-pairing principles, this reversible structural reconfiguration is also versatile; we show in particular that 1) it is compatible with various origami shapes, 2) it perfectly preserves fine structural details as well as site-specific functionality, and 3) it can be applied to dynamically address the spatial distribution of origami-tethered proteins.

Isothermal self-assembly of multicomponent and evolutive DNA nanostructures.

Thermal annealing is usually needed to direct the assembly of multiple complementary DNA strands into desired entities. We show that, with a magnesium-free buffer containing NaCl, complex cocktails of DNA strands and proteins can self-assemble isothermally, at room or physiological temperature, into user-defined nanostructures, such as DNA origamis, single-stranded tile assemblies and nanogrids. In situ, time-resolved observation reveals that this self-assembly is thermodynamically controlled, proceeds through multiple folding pathways and leads to highly reconfigurable nanostructures. It allows a given system to self-select its most stable shape in a large pool of competitive DNA strands. Strikingly, upon the appearance of a new energy minimum, DNA origamis isothermally shift from one initially stable shape to a radically different one, by massive exchange of their constitutive staple strands. This method expands the repertoire of shapes and functions attainable by isothermal self-assembly and creates a basis for adaptive nanomachines and nanostructure discovery by evolution.