A further contribution to the extreme variability of quadruplex structures from oligodeoxyribonucleotides containing inversion of polarity sites in the G-tract

Structural insight into DNA quadruplex structures formed by oligodeoxyribonucleotides 3'TG5'-5'GGGT3' (QS55) and 5'TG3'-3'GGGT5' (QS33) is presented. NMR analysis reveals that QS33 forms a parallel-like four-fold symmetric quadruplex, while QS55 possesses a two-fold symmetry and is characterized by a tetrameric antiparallel quadruplex embedded between two parallel tracts. The results reported here describe unprecedented quadruplex complexes provided by peculiar structural features never reported to date. These structures might inspire the design of new aptameric nucleic acids characterized by novel structural motifs hardly realizable with unmodified DNA/RNA.