Conformational Transition Of DNA Caused By Divalent Metal Ions

The interactions between divalent metal ions and DNA are essential for fundamental life processes.These interactions also have wide application value in technologies such as DNA-based ion sensors or DNA nanomachines.Current polyelectrolyte theories cannot describe these interactions well and do not consider the corresponding dynamics.In this study,we report the single-molecule dynamics of the binding of divalent metal ions to a single DNA molecule and the morphology characterization of metal?DNA complex.It was found that most of the divalent metal ions(Mn²⁺,Zn²⁺,Co²⁺,Ni²⁺,Cd²⁺),with the exception of Mg²⁺and Ca²⁺,could cause monomolecular DNA condensation.Alkali and alkaline-earth metal ions cannot cause significant changes in DNA length,while transition metal ions can cause DNA condensation.Critical ionic strengths of different ions that cause DNA condensation are different,and different shortening speeds were displayed in the dynamics,indicating ionic specificity.Atomic force microscopy scans showed that the morphological characteristics of the ion?DNA complexes were affected by the ionic strength of the metal ion,DNA chain length,and DNA concentration.At low metal ion concentration,DNA assumes a random coil conformation.Increasing the ionic strength,DNA shows a network-like condensed structures,suggesting that divalent metal ions can induce attraction between DNA molecules.In addition,increasing DNA concentration and increasing DNA chain length enhanced intermolecular interactions,resulting a higher degree of interconnectivity in the network structures.