I-motif-programmed functionalization of DNA nanocircles

The precise control of mechanical movements at the nanoscale remains a significant challenge for synthetic biology. Prior research has shown that DNA provides a versatile scaffold for constructing programmable molecular devices. However, existing methods for triggering structural changes often lack the required specificity for complex operations. This gap motivated the exploration of alternative structural motifs that respond to environmental stimuli. It was already known that i-motif structures form under acidic conditions through cytosine-rich sequences. That uncertainty drove the need to define how sequence length influences folding behavior. No prior work had resolved the specific parameters for integrating these motifs into larger circular architectures. This study addresses the need for tunable, proton-responsive components in DNA nanotechnology.

The study aims to expand the existing toolbox for controlling mechanical operations within DNA nanoarchitectures. Researchers sought to understand how the folding of intra- and intermolecular i-motif DNAs can be systematically regulated. The team investigated the influence of cytosine-tract length on the resulting structural topology. This effort was motivated by the need for more precise control over proton-responsive molecular devices. The authors addressed the challenge of integrating these motifs into larger, more complex DNA frameworks. They aimed to demonstrate that sequence-based programming allows for functionalizing double-stranded DNA nanocircles. The work explores the potential for these structures to act as proton-fueled machines. This investigation provides a framework for achieving diverse mechanical operations at the nanoscale.

The review approach involved systematic analysis of DNA folding through gel electrophoresis and circular dichroism. Researchers evaluated thermal denaturation to determine the stability of various cytosine-rich sequences. The team integrated these sequences into single-stranded gaps within double-stranded DNA nanocircles. They adjusted the length of cytosine tracts to modulate folding pathways. Fluorescence quenching served as the primary tool for monitoring the contraction and extension of the circles. The investigators utilized atomic force microscopy to visualize the resulting multicomponent architectures. This methodology allowed for the verification of different folding topologies. The approach focused on establishing a predictable relationship between sequence design and mechanical output.

The strongest finding indicates that cytosine-tract length primarily dictates whether i-motifs fold intra- or intermolecularly. Stretches of six or fewer residues favor intermolecular folding, while longer sequences promote intramolecular structures. Intramolecular motifs exhibit unusually high thermal stability under acidic conditions. These motifs enable reversible contraction and extension of the DNA circle, as confirmed by fluorescence quenching. Nanorings containing intermolecular i-motifs successfully induce the assembly of defined multicomponent architectures. These structures undergo structural changes such as dimerization and cyclization in response to proton triggers. The authors verified these complex topologies through gel electrophoresis and atomic force microscopy. The results confirm the nanocircle behaves as a functional proton-fueled prototype machine.

The authors demonstrate that i-motif folding behavior is directly tunable through the length of cytosine-rich tracts. These findings suggest that proton-responsive DNA nanocircles offer a reliable platform for mechanical control. The researchers propose that intramolecular folding facilitates reversible contraction and extension of circular structures. In contrast, intermolecular folding provides a mechanism for assembling complex multicomponent architectures. The study indicates that these nanocircles function as effective proton-fueled prototypes for molecular machinery. The authors highlight the potential for creating interlocked nanostructures such as rotaxanes and catenanes. These results imply that sequence-based programming allows for precise manipulation of DNA topology. The work provides a foundation for future applications in responsive molecular engineering.