Figure 3.

G-quadruplex structure, hydration and metal binding. (A) Side-view of the parallel ‘T-loops’ G-quadruplex shown within its well-defined 2F_o – F_c electron density map countered at 1.2 σ. (B) Two views related by a 90° rotation along the G-quadruplex helix axis, illustrating the hydration and metal ion binding of the G-quadruplex. The 3′ and 5′ ends of the G-quadruplex are indicated. Water molecules are shown in red, Na⁺ ions in grey and K⁺ ions in purple. The T-loops G-quadruplex is formed by the oligonucleotide sequence: 5′--3′. Guanines are color-coded in the sequence to indicate the guanine number forming each G-tetrad: , 5′G-tetrad, , middle G-tetrad and , 3′G-tetrad.