Here we couple experimental and simulative techniques to characterize the structural/dynamical behavior of a pH-triggered switching mechanism based on the formation of a parallel DNA triple helix. Fluorescent data demonstrate the ability of this structure to reversibly switch between two states upon pH changes. Two accelerated, half microsecond, MD simulations of the system having protonated or unprotonated cytosines, mimicking the pH 5.0 and 8.0 conditions, highlight the importance of the Hoogsteen interactions in stabilizing the system, finely depicting the time-dependent disruption of the hydrogen bond network. Urea-unfolding experiments and MM/ GBSA calculations converge in indicating a stabilization energy at pH 5.0, 2-fold higher than that observed at pH 8.0. These results validate the pH-controlled behavior of the designed structure and suggest that simulative approaches can be successfully coupled with experimental data to characterize responsive DNA-based nanodevices.
■ INTRODUCTIONDNA nanotechnology allows us to design and engineer smart nanomaterials and nanodevices using synthetic DNA sequences. 1−6 For example, current methodologies and synthetic strategies, such as DNA tiles, origami, or supramolecular assembly, allowed the production of complex nanostructures of different shapes and dimensions. 7−11 The unparalleled versatility of these approaches allows precise positioning of molecule-responsive switching elements in specific locations of DNA nanostructures, leading to the construction of more complex functional nanodevices. 12−14 Similarly, enzyme−DNA nanostructures have been demonstrated to enhance enzyme catalytic activity and stability. 15 DNA motifs that rely on noncanonical DNA interactions, such as G-quadruplex, triplex, i-motif, hairpin, and aptamers, can be used to design such nanodevices due to their dynamic-responsive behavior toward chemical and environmental stimuli. 16,17 These responsive units often respond to specific chemical inputs through a bindinginduced conformational change mechanism that leads to a measurable output or function. The efficiency of this class of responsive nanodevices strongly depends on the designed structure-switching mechanism that controls their activity or functionality. Therefore, there is an urgent need to understand the energies involved in these responsive systems and the relationship between their structure and dynamics. 16 Among such functional DNA nanodevices, those based on the triple-helix motif are attracting interest for their strong and programmable pH dependence. 18−20 By rationally incorporating triplex-forming portions into DNA nanodevices, it is possible to trigger conformational changes and functions using pH as a chemical input. 21−24 Despite the fair amount of knowledge of the basic design principles and mechanism of action of triplex-based nanodevices, no reports describing the connection between their structural and dynamical properties are available. Toward this aim, simulative approaches represent valuable tools to shed ...