Structural transition from the random coil to quadruplex of AG3(T2AG3)3 induced by Zn2+

Structures of G-quadruplex DNAs can be typically stabilized by monovalent cations such as K+, Na+. Some divalent and trivalent cations, such as Sr2+, Pb2+, Tb3+ and Eu3+, can also induce the formation of G-quadruplex DNA. Here we show that Zn2+ can induce the human telomeric sequence AG3(T2AG3)3 to fold the G-quadruplex structure by UV absorbance difference spectra and circular dichroism (CD) spectroscopy. At micromolar concentrations, the Zn2+-induced changes in the UV absorbance difference spectra and CD spectra are the characteristics of antiparallel G-quadruplexes although the long wavelength CD maximum is around 285 nm rather than the typical value of 295 nm. The binding stoichometry of Zn2+ per one AG3(T2AG3)3 molecule is four. To our knowledge, the structural transition of human telomeric sequence induced by Zn2+ was observed for the first time.