On the interaction of chromomycin A₃ with calf thymus DNA in the presence of metal cations at different pH values

Abstract

SynopsisThe interactions of the antitumor antibiotics, chromomycin A,, with a variety of metal cations in the pH range of 3.0-8.5 were systematically studied by CD, absorption, and 'H-nmr spectroscopies. Results were compared with thaw obtained in the presence of increasing amounts of calf thymus DNA. The negatively charged chromomycin A,, pK, 6.3, forms aggregates that become ordered and smaller in size, in the presence of variety of metal cations. Spectrophotometric titrations have shown that binding of the neutral drug to DNA at pH 4.5 does not require divalent cations, although the strength of the binding is greatly enhanced in their presence. At higher pH values ( > 7.0) and low DNA/drug ratio (< 20), the metal cations are necessary to induce the binding between chromomycin A, and DNA. At higher DNA/drug ratios (> 100 : I), an appreciable proportion of the drug is bound even in the absence of divalent cations. Its binding affinity to the DNA is enhanced in the presence of these cations and at low pH values. Therefore, we conclude that chromomycin A, binds to DNA in two related modes, in the presence and in the absence of divalent cations. The spectral data accumulated indicate the metal cation is involved in the binding of the drug to the DNA by forming a drug-metal-DNA ternary complex.

Crystal structure of the [Mg2+-(chromomycin A3)2]-d(TTGGCCAA)2 complex reveals GGCC binding specificity of the drug dimer chelated by a metal ion

“…Footprinting studies have also shown that both Chro and Mith require a G-C binding site that is at least three base pairs long (5,10). In addition to Mg 2+ , other divalent cations with a radius <0.85 A Ê are candidates for drug dimer formation (15,16). The solution structures of both complexes including the Mg 2+ -coordinated Chro±DNA complex (two drug equivalents per duplex) have been analyzed by nuclear magnetic resonance (NMR) spectroscopy (17±20).…”

Interaction of mithramycin with DNA

“…Up to now, only a few reports have appeared on this topic using CD spectroscopy [15,19,221. However, this technique is very interesting because of the large CD signal exhibited by these molecules and because of the sensitivity of the CD signal to a small modification in the molecular conformation.…”

“…However, up to now, conflicting values have been reported. Thus, Najak et al [I41 and Weinberger et al [15] have reported pK, values of 7 and 6.3, respectively. These determinations were performed at a drug concentration of approximately 50 pM and a varying temperature, most probably room temperature.…”

“…Numerous papers focus on the requirement of Mg2+ for the binding of Mit or chromomycin to DNA [12][13][14][15]18,191. We have previously shown that MgZf can be substituted by Zn2+, and that this cation is even more efficient than Mg" for the binding of Mit or chromomycin to DNA [l I].…”

Modelling basic features of specificity in DNA‐aureolic acid‐derived antibiotic interactions

“…While it is frequently considered that the presence of Mg2+ constitutes an absolute requirement for binding to occur [ 11,121, with, however, differing views on the ion's exact role and positioning [3,4,10], a recent publication [13] indicates that at pH 4.5 binding of the drug, which is present then in neutral monomeric form, does not require divalent cations (although the strength of binding is greatly enhanced in their presence). At pH > 7.0 and low DNA/drug ratios (< 20), metal cations are necessary, but at high DNA/drug ratios an appreciable proportion of the drug is bound even in the absence of the metal.…”