In What Ways Do Synthetic Nucleotides and Natural Base Lesions Alter the Structural Stability of G-Quadruplex Nucleic Acids?

Figure 2

Folding arrangements of the most often cited GQ structures. The intramolecular GQ architectures adopted by the 21-mer htel-21 G₃(TTAG₃)₃ oligodeoxynucleotide under various solution conditions, topologies 1–5. The basket-type antiparallel with 5′-to-3′ edgewise-diagonal-edgewise loops, forming in Na⁺ (topology 1); the chair-type antiparallel with three edgewise loops (topology 2); the (3 + 1 strands) hybrid-1 with propeller-like, edgewise, and edgewise loops (topology 3); the hybrid-2 with two edgewise loops followed by a propeller-type loop (topology 4), both hybrids forming in K⁺ solution; the parallel topology with all three loops in propeller-like configuration, as found in crystals containing K⁺ ions (topology 5); tetramolecular GQ assembling from four TGGGT DNA chains, [TG₃T]₄ (topology 6). Bottom panel: the two-tetrad, chair-type intramolecular antiparallel topology, folding from the 15-mer TBA oligodeoxynucleotide sequence shown below the topology. The syn dG nucleotides are indicated with underlined letters in italics. For references, see, for example, [8]. Shaded squares represent the G-tetrads displayed in Figure 1.