Distinct G-quadruplex structures of human telomeric DNA formed by the induction of sanguinarine and nitidine under salt-deficient condition.

The inducing abilities of two alkaloids, Sanguinarine (San) and Nitidine (Nit), to fold human telomeric DNA d[5'-TTGGG(TTAGGG)(3)A-3'] (H24A) into G-quadruplex structures has been investigated by using CD and (1)H NMR spectroscopy. It is found that, under salt-deficiency condition, San could induce H24A to fold into a normal anti-parallel G-quadruplex while Nit may induce hybrid or mixed-type G-quadruplex structures. In order to understand the structure of H24A induced by Nit, the interaction between Nit and existed hybrid G-quadruplex H24A in the presence of K(+) has been examined for comparison. The different behaviors of these two molecules interacted with DNA could be ascribed to distinct binding mode, which may be resulted from the steric hindrance of the molecular frame of these two alkaloids.