Intramolecular Folding of PolyT Oligonucleotides Induced by Cooperative Binding of Silver(I) Ions

Ag⁺-bridged T-Ag⁺-T was recently discovered in a Ag⁺-DNA nanowire crystal, but it was reported that Ag⁺ had little to no affinity to T nucleobases and T-rich oligonucleotides in solution. Therefore, the binding mode for the formation of this type of novel metallo base pair in solution is elusive. Herein, we demonstrate that Ag⁺ can interact with polyT oligonucleotides once the concentration of Ag⁺ in solution exceeds a threshold value. The threshold value is independent of the concentration of the polyT oligonucleotide but is inversely proportional to the length of the polyT oligonucleotide. The polyT oligonucleotides are intramolecularly folded due to their positively cooperative formation and the stack of T-Ag⁺-T base pairs, resulting in the 5′- and 3′-ends being in close proximity to each other. The intramolecular Ag⁺-folded polyT oligonucleotide has a higher thermal stability than the duplex and can be reversibly modulated by cysteine.