The effect of temperature on DNA structural transitions under the action of Cu²⁺ and Ca²⁺ ions in aqueous solutions

Abstract

The work examines the structural transitions of DNA under the action of Cu2+ and Ca2+ ions in aqueous solution at temperatures of 29 and 45 degrees C by ir spectroscopy. Upon binding to the divalent ions studied, DNA transits into the compact state both at 29 and 45 degrees C. In the compact state DNA remains in B-form limits. The compaction process is of high positive cooperativity. As temperature increases the divalent metal ion concentration required to induce DNA compaction decreases in the case of Cu(2+)-induced compaction and increases in the case of Ca(2+)-induced compaction. It is suggested that the mechanism of the temperature effect on DNA compaction in the presence of Cu2+ ions possessing higher affinity for DNA bases differs from that of the temperature influence on Ca(2+)-induced DNA compaction. In the case of copper ions the determining factor is the increase of binding constants of the Cu2+ ions interacting with the denatured parts formed on DNA while in the case of calcium ions it is the decreased screening action of counterions upon the increase of their hydration with temperature. The efficiency of divalent metal ions studied in inducing DNA compaction depends on hydration of counterions. DNA compaction occurs in a narrow interval of Cu2+ concentrations. As the Cu2+ ion concentration increases, DNA compaction is replaced with Cu(2+)-induced DNA aggregation. At elevated temperatures Cu(2+)-induced DNA compaction could acquire a phase transition character.

DNA interaction with biologically active divalent metal ions: binding constants calculation

“…In the compact state DNA remained in the B-conformation limits [1,2]. A further study allowed us to suggest that the mechanism of DNA condensation under Met 2+ ion action is not completely electrostatic but involves a partial destabilisation of DNA due to Met 2+ ion interaction with DNA bases [3,4].The present work is devoted to calculation of binding constants of divalent metal ions interacting with DNA in a condensation process. It should be noted that, as we have also shown in [1,2], at low concentrations Met 2+ ions binding to DNA occurred while DNA condensation was not observed.…”

“…In the compact state DNA remained in the B-conformation limits [1,2]. A further study allowed us to suggest that the mechanism of DNA condensation under Met 2+ ion action is not completely electrostatic but involves a partial destabilisation of DNA due to Met 2+ ion interaction with DNA bases [3,4].…”

“…When characterising DNA-metal ion binding there are three general questions that usually rise: what places on DNA a metal ion interacts with (binding sites); how the interaction effects the DNA structure; and what is the affinity of the binding. In our previous work [1][2][3], we studied the interaction of Cu 2+ , Mn 2+ and Ca 2+ ions with DNA macromolecule in aqueous and water-alcohol solutions at different metal ion concentrations. We have shown that all these ions interact both with the bases and with phosphate groups of DNA (at different [Met 2+ ]/[DNA] ratios, see [1][2][3]).…”

“…In our previous work [1][2][3], we studied the interaction of Cu 2+ , Mn 2+ and Ca 2+ ions with DNA macromolecule in aqueous and water-alcohol solutions at different metal ion concentrations. We have shown that all these ions interact both with the bases and with phosphate groups of DNA (at different [Met 2+ ]/[DNA] ratios, see [1][2][3]). When interacting with DNA in an aqueous solution divalent metal (Met 2+ ) ions studied induce DNA structural transitions similar to the DNA transition into compact state upon interaction with 3 + ions or polyamines-namely, a drastic decrease in the volume occupied by DNA molecules with reversible formation of DNA dense particles of well-defined size and ordered morphology.…”

“…The main experimental method used by us in [1][2][3][4] was IR spectroscopy. We have found that upon DNA interaction with Met 2+ ions the intensities of the absorption bands of DNA phosphate groups and bases increase significantly.…”