Ethanolamine Derivatives Prompt Oxidation-Mediated Cleavage of Phosphorothioated DNA via Redox Control and Competition with Desulphurization

Abstract

Abstract In the early 2000s, an epoch-making discovery of phosphorothioated DNA (PS-DNA, also as medicines) was made to show that sulfur atoms are present on the DNA backbone in microorganisms. However, its reaction activity and mechanism have not been well clarified. We show that PS-DNA is cleaved efficiently via oxidation, but not previously believed alkylation; this sulfur modification can be repaired by desulphurization once the sulfhydryl is further oxidized. When Tris or other ethanolamine derivatives are present, the cleavage becomes extremely efficient. Analyzed by enzymatic digestion, ligation, and mass spectroscopy, a mechanism is proposed to explain effects of ethanolamine derivatives and the competition between repair and breakage. Tris favors cleavage by keeping and utilizing the oxidation at –S(O)OH (sulfinic group) stage. The hydroxyl group on ethanolamine derivatives attacks the activated phosphor atom for cleavage with an intramolecular-like mode to form simultaneously a phosphoester bond. Desulphurization is dominant once the PS-DNA is oxidized to –S(O2)OH (sulfonic group). We believe that the biological significance of PS-DNA is protection of DNA nucleobases from weak oxidants by direct repairing or cleavage-repairing approach, which is affected by amines. Besides understanding the biological significance of PS-DNA, our findings will contribute greatly to developing new bio-techniques and nucleic acid medicines.