Effect of basic oligopeptides on the B‐Z transition of poly(dG‐dC)·poly(dG‐dC) in water–methanol solutions

Abstract

The effect of basic oligopeptides (Lys-Ala-Ala)n (n = 1-5, 10) and (Lys-Leu-Ala)n (n = 1-4) on the B-Z transition of poly(dG-dC).poly(dG-dC) in water-methanol solutions was investigated using CD and uv spectroscopy. In the absence of peptides, the concentration of methanol at the midpoint of the B-Z transition is 64% at 25 degrees C. The transition is temperature dependent and the B conformation is preferred at higher temperatures. All peptides tested shift the midpoint of the B-Z transition to lower concentrations of methanol. For shorter peptides this effect increases with an increasing number of monomeric units, showing the importance of the number of positive charges in the peptide molecule. Al conditions of low methanol content, the trimer and tetramer of the (Lys-Leu-Ala)n series have a greater effect on the B-Z transition than the corresponding oligomers of the (Lys-Ala-Ala)n series. This indicates an important influence of the presence of hydrophobic groups in the peptide side chains on the binding. In the presence of peptides, the B-Z transition is also temperature dependent and the B conformation is preferred at higher temperatures. The addition of peptides results in an increase of the transition midpoint and of the transition width. These parameters were used for the calculation of the transition enthalpy delta HB-Z in 65% methanol, which is -1.15 +/- 0.25 kcal/base pair. Since the van't Hoff enthalpy delta HVH calculated from the temperature dependence of the B-Z transition in the absence of peptides is -130 kcal/mol, the length of the cooperative unit is about 110 base pairs. The results suggest that the mechanism of Z-DNA induction is similar but not identical with that involved in the action of metal cations in aqueous solution.

Stabilization of Triple-Helical Nucleic Acids by Basic Oligopeptides

“…Upon addition of basic oligopeptides or polypeptides, the melting temperatures of RNA and DNA are elevated, indicating an increased stability of the double helix (Tsuboi et al, 1966;Olins et al, 1968;Gabbay et al, 1973;Mandel & Fasman, 1974). Lysinecontaining peptides with (Ala-Lys)", (Gly-Lys)", (Lys-Ala-Ala)", and (Lys-Leu-Ala)" sequences act in a manner similar to that of polyamines in inducing Z-DNA (Takeuchi et al, 1991(Takeuchi et al, , 1994Votavova et al, 1991;Votavova & Sponar, 1993). Our data extend the list of DNA structures known to be stabilized by basic oligopeptides to include intermolecular triplex DNA.…”

“…The resulting effect of netropsin on non B structures is a destabilization of the Z form (Zimmer et al, 1983) or the (dT)"-(dA)"*(dT)" triplex (Durand et al, 1992;Park & Breslauer, 1992). The largely electrostatic interactions between the numerous positive charges of basic peptides (e.g., polylysine) and the negative charges of DNA effectively stabilize the Z form (Takeuchi et al, 1991(Takeuchi et al, , 1994Votavova et al, 1991;Votavova & Sponar, 1993) residues, and basic oligopeptides may provide a model for surface-localized protein domains which might interact with triple-helical nucleic acids. The histones, which are used to package the entire genome into chromatin, are abundant in lysine.…”