Thermodynamic investigation of M-DNA: a novel metal ion–DNA complex

• Published in: Journal of inorganic biochemistry 2003-02, Vol.94 (1), p.94-99
• Main Authors: Wettig, Shawn D., Wood, David O., Lee, Jeremy S.
• Format: Article
• Language: English
• Subjects: DNA - chemistry; Enthalpies; Isothermal titration calorimetry; M-DNA; Metals - chemistry; Metal–DNA complex; Spectrophotometry, Ultraviolet; Thermodynamics
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/S0162-0134(02)00624-4

The thermodynamics of formation of a novel divalent metal ion–DNA complex known as M-DNA have been investigated using an ethidium bromide (EB) fluorescence assay, and with isothermal titration calorimetry. The process of M-DNA formation was observed from the EB assay to be strongly temperature-dependent. The binding of Zn 2+ to calf thymus (42% GC content) and Escherichia coli (50% GC content) DNA at pH 8.5 exhibited an endothermic cooperative binding process at Zn 2+ concentrations of approximately 0.1 mM, indicating an entropy driven process. This binding process is consistent with a site-specific binding interaction, similar in nature to Z-DNA formation; however, the interaction occurs at much lower metal ion concentrations. The enthalpy of M-DNA formation for calf thymus DNA was determined to be 10.5±0.7 and 9±2 kJ/mbp at DNA concentrations of 100 and 50 μg ml −1, respectively. An enthalpy of 13±3 kJ/mbp was obtained for M-DNA formation for 50 μg ml −1 E. coli DNA. No evidence of M-DNA formation was observed in either DNA at pH 7.5 with Zn 2+ or at either pH 7.5 or 8.5 with Mg 2+.