Stabilization of a Bimolecular Triplex by 3′-S-Phosphorothiolate Modifications: An NMR and UV Thermal Melting Investigation

• Published in: Chemistry : a European journal Vol. 21; no. 19; pp. 7278 - 7284
• Main Authors: Evans, Kathryn, Bhamra, Inder, Wheelhouse, Richard T., Arnold, John R. P., Cosstick, Richard, Fisher, Julie
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 04.05.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: 3′-S-phosphorothiolate; Binding; Biological; Chemistry; Deoxyribonucleic acid; DNA; DNA - chemistry; DNA structures; Grooves; Melting; Models, Molecular; Molecular biology; NMR spectroscopy; Nuclear Magnetic Resonance, Biomolecular; Nucleic Acid Conformation; Nucleic Acid Denaturation; Nucleic acids; Phosphates - chemistry; Ribonucleic acids; Stabilization; Strands; Thermodynamics; UV thermal melting; UV thermal melting; nucleic acids; NMR spectroscopy; 3′-S-phosphorothiolate; DNA structures
• DOI: 10.1002/chem.201500369
• ISSN: 0947-6539; 1521-3765

Triplexes formed from oligonucleic acids are key to a number of biological processes. They have attracted attention as molecular biology tools and as a result of their relevance in novel therapeutic strategies. The recognition properties of single‐stranded nucleic acids are also relevant in third‐strand binding. Thus, there has been considerable activity in generating such moieties, referred to as triplex forming oligonucleotides (TFOs). Triplexes, composed of Watson–Crick (W–C) base‐paired DNA duplexes and a Hoogsteen base‐paired RNA strand, are reported to be more thermodynamically stable than those in which the third strand is DNA. Consequently, synthetic efforts have been focused on developing TFOs with RNA‐like structural properties. Here, the structural and stability studies of such a TFO, composed of deoxynucleic acids, but with 3′‐S‐phosphorothiolate (3′‐SP) linkages at two sites is described. The modification results in an increase in triplex melting temperature as determined by UV absorption measurements. 1H NMR analysis and structure generation for the (hairpin) duplex component and the native and modified triplexes revealed that the double helix is not significantly altered by the major groove binding of either TFO. However, the triplex involving the 3′‐SP modifications is more compact. The 3′‐SP modification was previously shown to stabilise G‐quadruplex and i‐motif structures and therefore is now proposed as a generic solution to stabilising multi‐stranded DNA structures. Triplex stabilization: NMR spectroscopy and UV thermal melting studies reveal that the structure and thermodynamic properties of a bimolecular triplex containing two 3′‐S‐phosphorothiolate modifications are enhanced compared with those for the native system (see figure). This result, together with similar observations for a G‐tetraplex and an i‐motif, suggests that the 3′‐S‐phosphorothiolate modification provides a subtle approach to the stabilization of multi‐stranded DNA complexes in general.