Enzyme Reactions Are Accelerated or Decelerated When the Enzymes Are Located Near the DNA Nanostructure.

It is known experimentally that enzymatic reactions are often accelerated when the enzymes are assembled on the scaffold of DNA nanostructures. However, the exact mechanism by which this acceleration occurs remains unclear. Here, we study the reactions of enzymes with different catalytic mechanisms assembled on a DNA scaffold with various substrates. Analysis of the hydration properties of the substrates using our accurate statistical mechanics theory classifies the substrates into two groups that behave as hydrophilic and hydrophobic solutes, respectively. The reaction of the enzyme on the DNA scaffold is accelerated with a hydrophilic substrate but decelerated with a hydrophobic substrate. We propose a mechanism of acceleration or deceleration in which, due to the formation of a high-density layer of water near the DNA surface with high negative charge density, the concentration of a substrate with high energetic affinity for water within the layer becomes higher than that near a free enzyme, whereas that of a substrate with low energetic affinity becomes lower within the layer. This study provides chemical and physical insights into a general case of biocatalysts, where the rates of chemical reactions occurring at the interface of biomolecules in aqueous environments can differ substantially from those in the bulk solution due to variations in the local concentration of a given ligand.