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 Ln-DNA interaction at the level of a single DNA molecule. Different DNA-metal complexes were produced by the addition of the five lanthanide ions, La, Ce, Pr, Tb, and Ho 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, Ho 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 Ln-DNA complex solutions were restored to their original length with different restoration speeds, by the addition of EDTA, and this further indicated that the Ho 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.