Is There Any Proton Exchange Between Ammonium Ions localized Within the d(G3T4G4)2 Quadruplex?
It is generally appreciated that stability, dynamics and function of nucleic acids are affected by nature of cations that are involved in interaction with specific functionalities. DNA G-quadruplexes are unique among nucleic acid structures in their metal ion requirements. Cations inside G-quadruplex structures have been shown to exchange between binding sites and bulk solution. However, in d(G3T4G4)2 G-quadruplex ammonium ions do not exchange through the central G-quartet plane. Passage of larger cations through a G-quartet such as potassium or ammonium ions requires partial opening of G-quartets. The use of HzExHSQC experiment demonstrates that smaller protons move through the central G-quartet plane.
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