DNA interaction with Mn²⁺ ions at elevated temperatures: VCD evidence of DNA aggregation

Abstract

Interaction of natural calf thymus DNA with Mn(2+) ions was studied at room temperature and at elevated temperatures in the range from 23 degrees C to 94 degrees C by means of IR absorption and vibrational circular dichroism (VCD) spectroscopy. The Mn(2+) concentration was varied between 0 and 1.3M (0 and 10 [Mn]/[P]). The secondary structure of DNA remained in the frame of the B-form family in the whole ion concentration range at room temperature. No significant DNA denaturation was revealed at room temperature even at the highest concentration of metal ions studied. However at elevated temperatures, DNA denaturation and a significant decrease of the melting temperature of DNA connected with a decrease of the stability of DNA induced by Mn(2+) ions occurred. VCD demonstrated sensitivity to DNA condensation and aggregation as well as an ability to distinguish between these two processes. No condensation or aggregation of DNA was observed at room temperature at any of the metal ion concentrations studied. DNA condensation was revealed in a very narrow range of experimental conditions at around 2.4 [Mn]/[P] and about 55 degrees C. DNA aggregation was observed in the presence of Mn(2+) ions at elevated temperatures during or after denaturation. VCD spectroscopy turned out to be useful for studying DNA condensation and aggregation due to its ability to distinguish between these two processes, and for providing information about DNA secondary structure in a condensed or aggregated state.

The effect of manganese(II) on the structure of DNA/HMGB1/H1 complexes: Electronic and vibrational circular dichroism studies

“…They are summarized in Table I based on a recent review 46 and two analyses of DNA interacting with manganese ions. 52,65 Carbonyl Region. Most of the absorption and VCD features of DNA (r ¼ R ¼ 0.0) between 1750 and 1450 cm À1 (Figure 4) originate from C¼ ¼O stretching and skeletal ring vibrations of the nitrogenous bases.…”

Fourier transform infrared/vibrational circular dichroism spectroscopy as an informative tool for the investigation of large supramolecular complexes of biological macromolecules

“…As the IR spectrum of DNA has been well characterized previously, [32][33][34][35]37 only some specific assignments germane to the discussion are summarized in Table I. Of principal significance here is the region between $1710 and 1620 cm À1 (Figure 3) consisting of the C¼ ¼O stretching modes of all four bases.…”

“…[32][33][34][35] The assignments for DNA (Figure 3) are discussed in detail elsewhere 30 and are briefly summarized in Table I.…”

“…An absorption at 1648 cm À1 (Figure 3a), which is due to overlapping carbonyl stretching coupled with in-plane ring vibrations of cytosine and C4¼ ¼O4 of thymine, shifts to 1646 cm À1 at r ¼ 0.3, and further to 1643 cm À1 at r ¼ 0.6 ( Figure 5a). The shoulder at 1623 cm À1 arising from overlapping in-plane ring vibrations of adenine, thymine, and cytosine 34,35 shows no significant wavenumber shifts. The corre- sponding shoulder at 1640 cm À1 in VCD of DNA due to adenine and thymine transforms into a couplet at 1636(þ)/1620(À) cm À1 (Figure 4b).…”

“…The intensity of this band gradually increases with increasing r, but significantly drops at r ¼ 0.9, revealing the negative band of cytosine at 1504 cm À1 attributed to C¼ ¼N stretching. 35,38 Another strong negative VCD peak of the complex at r ¼ 0.9 emerges around 1575 cm À1 and might be attributed to the increasing VCD signal of Asp and Glu sidechain vibrations. 36 The strongest absorption between 1150 and 750 cm À1 arises from the symmetric vibration of the O¼ ¼P¼ ¼O group (Figures 4a and 5a).…”