Book of Abstracts: Albany 2003
June 17-21 2003
Model of Formation of Liquid-Crystalline Dispersions in the Process of the DNA-Chitosan Binding
The binding of Chitosan on DNA can, under certain conditions, lead to formation of liquid-crystalline dispersion (LCD). Experimental data (Fig. 1A) of the formation of LCD has been taken from (1). Here a model of the binding of Chitosan to DNA is being developed, which is capable to describe the formation of LCD as a process of DNA condensation under equilibrium binding of Chitosan to DNA. Given a certain concentration of Chitosan, DNA molecules with different numbers of bound ligands can be found in equilibrium in the solution. As soon as the number of Chitosan ligands covering one DNA molecule exceeds a certain critical value, this molecule will transit to a different state, which accounts for those DNA that are able to interact and form LCD (Fig. 1B).
Figure 1A: Formation of LCD by binding of Chitosan to DNA. Cchit means the concentration of Chitosan in the solution, and R the signal of CD spectrum, which accounts for the formation of LCD (in relative units). Solid squares indicates experimental data points from (1).
Figure 1B: Transition between the two states of DNA, and formation of LCD when DNA molecule is fully covered by Chitosan.
The formation of LCD through the bounding of Chitosan with DNA can be described by equations, which have been derived earlier (2). Let L be the number of base pairs of the DNA molecule, that are covered by one single ligand, and K be the intrinsic binding constant of one single Chitosan with DNA. In Figure 1A one can see as a solid line the theoretical curve calculated with K = 1.5x107M-1 and L = 45 for Chitosan with a molecular weight of 19 kDa. We can denote that the critical coverage of DNA by Chitosan molecules is about 80%. This quantity corresponds to level of charge compensation for the condensation of the DNA by polyamines (3).
Yu. D. Nechipurenko1,3
1V. A. Engelhardt Institute of Molecular Biology