Guanine-rich DNA sequences can fold into four-stranded, noncanonical secondary structures called G-quadruplexes (G4s). G4s were initially considered a structural curiosity, but recent evidence suggests their involvement in key genome functions such as transcription, replication, genome stability, and epigenetic regulation, together with numerous connections to cancer biology.
The capacity for guanylic acid derivatives to self-aggregate was noted over a century ago. Some 50 years later, fibre diffraction revealed that guanylic acids form four-stranded, righthanded helices leading to a proposed model in which the strands are stabilised via Hoogsteen hydrogen-bonded guanines to form co-planar G-quartets.
However, why guanine specifically? Why not adenine, thymine, or cytosine quadruplex?
It could be because guanine can create more hydrogen bonds that stabilize the g-quadruplex structure.
Interesting question.
It appears to me that the G is rich in lone pair electron in the nitrogen base, which makes the G partially negative, which will associate with binding electrostatically with the cation potassium in the center of quadruplexes.
There is cytosine quadruplex too, it's called i-motif. I-motifs appear in the complement to G-rich DNA strand.
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