The role of Na+ in catalysis by the 8–17 DNAzyme

Abstract

The 8–17 DNAzyme is the most studied deoxyribozyme in terms of its molecular mechanism; hence it has become a model system to understand the basis behind DNA catalysis. New functional studies and the recent attainment of high-resolution X-ray structures, in addition to theoretical calculations have offered a great opportunity to gain a broader comprehension of its mechanism; however many aspects are unclear yet, especially regarding the precise role of metal ions in catalysis. Recently, molecular dynamics simulations have suggested for the first time a specific and dynamical participation of Na⁺ in the mechanism through the reaction pathway, besides the roles proposed for divalent metal cofactors. Herein, we present experimental evidence of a cooperative role of the monovalent cation Na⁺ in catalysis that is in line with these theoretical suggestions. Our findings show a clear influence of the concentration of Na⁺ on the activity of the 8–17 DNAzyme when Pb²⁺ is used as the cofactor. Interestingly, this effect is not noticed with Mg²⁺, indicating a particular contribution of the monovalent ion to catalysis that would operate preferentially with Pb²⁺. We have also found that Na⁺ affects the pK_a of the general base and the general acid, indicating its influence on general acid–base catalysis, already identified as part of the mechanism of the 8–17 DNAzyme. Finally, our results emphasize the need to consider Na⁺ carefully in the design and analysis of functional studies of catalytic DNAs and its possible specific role in their mechanisms.