Thermostability Trends of TNA:DNA Duplexes Reveal Strong Purine Dependence

The development of high fidelity polymerases and streamlined synthesis of threose nucleic acid (TNA) triphosphates and phosphoramidites has made TNA accessible as a motif for generating nuclease-resistant high-affinity aptamers, antisense oligos, and synthetic genetic biopolymers. Little is known, however, about the thermostability trends of TNA:DNA duplexes. Here we investigate the thermostability of 14 TNA:DNA duplexes with the goal of elucidating the fundamental factors governing TNA:DNA duplex stability. We find that purine content in TNA significantly influences the stability and conformation of TNA:DNA duplexes. Low TNA purine content destabilizes duplexes, with T_m values often 5 °C lower than analogous DNA:DNA and RNA:DNA duplexes. By contrast, TNA:DNA duplexes having high TNA purine content display greater stability than DNA:DNA or RNA:DNA duplexes having the same sequences. High TNA purine content leads TNA:DNA duplexes to adopt conformations similar to RNA:RNA (A-form) configuration, whereas duplexes with low TNA purine content have conformations more similar to DNA:DNA (B-form) configuration. These insights provide a basis for understanding and predicting TNA:DNA duplex stability, which is anticipated to guide the practical use of TNA in biotechnology applications.