Lanthanide ions induce DNA compaction with ionic specificity

Lanthanide (Ln) cations exhibit unique properties that include the ability to interact with DNA to form metal-DNA complexes, which are of great interest in medical, biological and nano-technological fields. Both experimental and theoretical studies have not completely addressed the interaction dynamics between lanthanide ions and DNA. The present study investigates the dynamics of the Ln³⁺-DNA interaction at the level of a single DNA molecule. Different DNA-metal complexes were produced by the addition of the five lanthanide ions, La³⁺, Ce³⁺, Pr³⁺, Tb³⁺, and Ho³⁺ to the DNA solutions. The binding dynamics indicated that the lanthanide cations can induce DNA compaction in a concentration and force-dependent manner. Ionic specificity was displayed in the single-molecule interaction dynamics, where, Ho³⁺ was found to be the most efficient lanthanide to cause DNA compaction, which was verified by the morphological characterization. The DNA molecules in the five Ln³⁺-DNA complex solutions were restored to their original length with different restoration speeds, by the addition of EDTA, and this further indicated that the Ho³⁺ ion had the strongest affinity toward DNA. We conclude that counterion correlation cannot solely explain the ion-dependent DNA compaction, and ionic specificity should be considered significant.