Interaction of DNA with poly(L-Lys-L-Ala-Gly) and poly(L-Lys-L-Ala-L-Pro). Circular dichroism and thermal denaturation studies

Abstract

Complexes of DNA with polypeptides composed of Lys, Ala, and Gly in both a sequential order, poly(L-lysine-L-alanine-glycine), and a statistical distribution, poly(L-lysine36-L-alanine28-glycine), were prepared using gradient dialysis. These polypeptide-DNA complexes were studied using ultraviolet absorption (UV) and circular dichroism (CD) to probe the conformation, binding, and melting behavior of DNA in the complex. Complexes with the sequential polypeptide showed no structural change in the DNA; however, the complexes with the random polypeptide yield CD spectra similar to phi DNA [Maniatis, T., Venable, Jr., J.S., and Lerman, L.S. (1974), J. Mol. Biol. 84, 37]. A second sequential polypeptide, poly(L-Lys-L-Ala-L-Pro)n, -DNA complex was also studied. It was found to exhibit pronounced structural changes as a function of ionic strength and poly-peptide-DNA ratio, more similar to the random sequence that the ordered sequence of the Lys, Ala, Gly polymer. Thus the importance of the composition and amino acid sequence in polypeptides which bind to DNA, even in such simple systems, is demonstrated. Evidence from thermal denaturation, employing simultaneous monitoring of CD and UV changes, supports a model in which specific polypeptides cause condensation of the DNA in the complex into an asymmetric tertiary structure. The relevance of these model systems to chromatin is discussed.

Thermal denaturation of chromatin and lysine copolymer–DNA complexes. Effects of ethylene glycol

“…32 The CD spectra in the presence of glycol show no evidence of +-like spectra. The derivative absorption melting profile In the presence of 1M ethylene glycol, the derivative absorption melting profile of p~l y (~-L y~, L-Ala, G1y)-DNA (Fig.…”

Stability of ionic complexes prepared from plasmid DNA and self-aggregated chitosan nanoparticles

“…18 However, residual hyperchromicity may exist because of incomplete base pairing between the complementary strands. 20 The residual hyperchromicity of DNA formed complexes with chitosan self-aggregates was larger than that of DNA alone (Table I). This may have been due to the disruption of base-pairing by the chitosan self-aggregates during the annealing process.…”

Circular dichroism studies on chromatin models

“…At these points, sample complexes were removed and CD spectra taken the salt decreased below a critical concentration (< 0.25 M NaCI) the C-like CD spectral magnitudes decreased and returned to a B-form DNA spectrum at low ionic strength. The CD spectra of polypeptide-DNA complexes can manifest a condensed type of pattern (C, Y, A) at a given r by varying the ionic strength or at a given ionic strength by varying r [3]. This functional dependence requires a unique phase transition to the condensed form, analogous to liquid crystal formation discussed by Ong et al [14].…”