Probing the effect of minor groove interactions on the catalytic efficiency of DNAzymes 8-17 and 10-23

Abstract

DNAzymes (Dz) 8-17 and 10-23 are two widely studied and well-characterized RNA-cleaving DNA catalysts. In an effort to further improve the understanding of the fragile interactions and dynamics of the enzymatic mechanism, this study examines the catalytic efficiency of minimally modified DNAzymes. Five single mutants of Dz8-17 and Dz10-23 were prepared by replacing the adenine residues in the corresponding catalytic cores with 3-deazaadenine units. Kinetic assays were used to assess the effect on the catalytic activity and thereby identify the importance of hydrogen bonding that arises from the N3 atoms. The results suggest that modifications at A 15 and A 15.0 of Dz8-17 have a significant influence and show a reduction in catalytic activity. Modification at each location in Dz10-23 results in a decrease of the observed rate constants, with A 12 appearing to be the most affected with a reduction of ∼80% of k obs and ∼25% of the maximal cleavage rate compared to the wild-type DNAzyme. On the other hand, modification of A 12 in Dz8-17 showed an ∼130% increase in k obs, thus unraveling a new potential site for the introduction of chemical modifications. A pH-profile analysis showed that the chemical cleavage step is rate-determining, regardless of the presence and/or location of the mutation. These findings point towards the importance of the N3-nitrogens of certain adenine nucleotides located within the catalytic cores of the DNAzymes for efficient catalytic activity and further suggest that they might directly partake in maintaining the appropriate tertiary structure. Therefore, it appears that minor groove interactions constitute an important feature of DNAzymes as well as ribozymes.