Sharp Switching of DNAzyme Activity through the Formation of a Cu^II -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.