Sharp Switching of DNAzyme Activity through the Formation of a CuII-Mediated Carboxyimidazole Base Pair

DNAzymes are widely used as functional units for creating DNA-based sensors and devices. Switching of DNAzyme activity by external stimuli is of increasing interest. Herein we report a Cu-II-responsive DNAzyme rationally designed by incorporating one of the most stabilizing artificial metallo-base pairs, a Cu-II-mediated carboxyimidazole base pair (Im (c)-Cu-II-Im (c)), into a known RNA-cleaving DNAzyme. Cleavage of the substrate was suppressed without Cu-II, but the reaction proceeded efficiently in the presence of Cu(II)ions. This is due to the induction of a catalytically active structure by Im (c)-Cu-II-Im (c) pairing. The on/off ratio was as high as 12-fold, which far exceeds that of the previously reported DNAzyme with a Cu-II-mediated hydroxypyridone base pair. The DNAzyme activity can be regulated specifically in response to Cu(II)ions during the reaction through the addition, removal, or reduction of Cu-II. This approach should advance the development of stimuli-responsive DNA systems with a well-defined sharp switching function.