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Albany 2001

category image Biomolecular
Stereodynamics
SUNY at Albany
June 19-23, 2001

A Comparative Study of DNA Binding to Mg(II) and Ca(II) in Aqueous Solution By Capillary Electrophoresis and FTIR Spectroscopic Methods

The crystal structures of Mg(II) and Ca(II) complexes with B-DNA decamers CCAACGTTGG and CCAGCGCTGG and with GCGAATTCGCG, were recently determined at atomic resolution (Chiu & Dickerson, J. Mol. Biol. 301, 915-945, 2000 and Minasov et al., J. Mol. Biol. 291, 83-99, 1999). Major structural differences regarding the cation binding modes (major and minor groove bindings), specific and nonspecific interactions as well as DNA bending are reported. Ca binds directly and indirectly to DNA bases and the backbone phosphate group, while Mg coordination is mainly indirectly (via cation hydration shell). Although, detailed structural differences for Mg-DNA and Ca-DNA are provided in the solid state (1,2), such comparative study in aqueous solution has been less investigated. Now we report the interaction of Mg and Ca cations with calf-thymus DNA in aqueous solution at physiological pH, using constant concentration of DNA (1.25 mM) and various concentrations of metal ions (2 µM to 650 µM). Capillary electrophoresis, UV-visible and FTIR spectroscopic methods were used to determine the cation binding modes, the binding constants and the DNA structural variations in aqueous solution. Direct Ca-PO2 binding was evident by major spectral changes (shifting and splitting) of the back bone PO2 asymmetric streching at 1222 cm-1 with K=4.80 x 105 M-1, whereas an indirect Mg-phosphate interaction was observed (due to the lack of shifting and splitting of the phosphate band at 1222 cm-1) with K= 3.20 x 105 M-1. The metal-base binding was indirectly with K= 3.0 x 104 M-1 for Ca cation and K= 5.64 x 104 M-1 for Mg cation. Similar binding constants were observed for DNA adducts with Mg porphyrin complexes (3). Both major and minor groove bindings were observed with minor perturbations of B-DNA structure.

References and Footnotes
  1. T. K. Chiu and R. E. Dickerson, J. Mol. Biol. 301, 915-945 (2000).
  2. G. Minasov, V. Tereshko and M. Egli, J. Mol. Biol. 291, 83-99 (1999).
  3. J. F. Neault and H. A. Tajmir-Riahi, Biophys. J. 76, 2177-2182 (1999).

H. A. Tajmir-Riahi, H. Arakawa, H. Malonga, R. Ahmad

Department of Chemistry-Biology, University of Québec at Trois-Riviéres, C.P. 500, TR (Quebec) Canada G9A 5H7 *Phone 819-376-5052 (ext: 3310) Fax: 819-376-5084 E.mail: tajmirri@uqtr.uquebec.ca