Dynamism and evolvability in nucleic acid enzymes.

Protein dynamism and evolvability are key parameters linking enzyme flexibility to adaptive potential, yet how these concepts apply to nucleic acid enzymes remains largely unexplored. Here, we propose that threose nucleic acid (TNA), a genetic polymer that is more conformationally restricted than DNA, may be evolutionarily constrained by its preorganized backbone. RNA-cleavage profiles comparing the well-known 10-23 DNA enzyme (DNAzyme) with two in vitro selected TNA enzymes (threozymes) reveal striking differences in their temperature dependence. While the DNAzyme catalyzed reaction is optimal at 37 °C and weakly active at 50 °C, threozymes display the opposite trend, suggesting that TNA catalysis must overcome a higher free-energy barrier than DNA catalysis. Consistent with this view, the reaction becomes less temperature dependent for threozymes that operate with more flexible active sites. Together, these findings highlight the importance of backbone structure as a critical parameter for evolvability with implications for RNA world models and biomedical applications.