An Unprecedented Knot‐like G‐Quadruplex Peripheral Motif

A knot‐like G‐quadruplex peripheral structure is formed by a 7‐nt DNA sequence DL7 (TGTTGGT), in which six out of its seven nucleobases participate in compact base‐pairing interactions. Here, the solution NMR structure of a 24‐nt DNA oligonucleotide containing the DL7 sequence shows the interaction between a two‐layer anti‐parallel G‐quadruplex core and the peripheral knot‐like structure, including the construction of two sharp turns in the DNA backbone. The formation of this novel structural element highlights the intricate properties of single‐stranded DNA folding in presence of G‐quadruplex‐forming motifs. We demonstrated the compatibility of the DL7 knot‐like structure with various G‐quadruplexes, which could have implications in drug design and DNA engineering.