Molecular architecture apporach is proposed to fabricate some nanolayer models of one important cell structure named DNA-membrane contact. These models are belived to clarify the role of the lipid component of the contact in its function and structure. Two-dimensionally organized multilayer films of DNA complexes with the natural lipid sphingosine and the synthetic cationic amphiphiles hexadecylamine and hexadecyltrimethylammonium bromide were obtained as such models.
The films were prepared by Langmuir-Blodgett technology (LB-films) and by the method based on consecutively alternating adsorption of components on a solid plate (SA-films). IR/UV-spectroscopy and small-angle X-ray scattering were used to obtain data on the organization and the kind of packing of the lipid and nucleic component of the complex; to identify the groups and the types of the interactions responsible for complex formation; to establish the conformational state of DNA in the complex. In particular, the presence in the IR spectrum at a high relative humidity (r.h.) of a 1712 cm-1 band attributed to the vibrations of the carbonyl group of guanine and the C4=O group of thymine in the stacking base pairs and the appearance of a narrow intensive 1088 cm-1 band from the symmetric oscillation of the phosphate group, as well as 1052 and 1020 cm-1 bands from vibrations of the deoxyribose fragment suggest that the DNA in the SA-film complex with hexadecyltrimethylammonium bromide is in the double-helical state. The absence of these bands in the IR spectra of wet films of the DNA-hexadecylamine and DNA-sphingosine complexes point to that the DNA is unwound. There are also differences in the r.h.dependences of the spectral parameters of IR bands of the nucleic components of films between these two types of complexes.
With increasing r.h. from 0 to 93% the changes in the IR spectrum of the SA-film of the DNA-hexadecyltrimethylammonium are determined not only by hydration of various fragments of the sugar-phosphate chain and nitrous bases but also by the conformational changes of DNA from an unordered state to the double helix, whereas in the case of the SA-film of the DNA-hexadecylamine and of the LB-film of DNA-sphingosine no conformational changes occur, similarly as observed for the free denatured DNA. Unlike hexadecylamine and sphigosine, hexadecyltrimethylammonium in which hydrogen atoms of the ammonium fragment are replaced by CH3 groups is unable to form hydrogen bonds. It can be assumed that the unwinding of DNA in the complexes with hexadecylamine and sphingosine occurs due to replacement of intramolecular base-base H-bonds by intermolecular base-amine H-bonds.
These results are supported by the data of small-angle X-ray scattering. The obtained evidence enables the suggestion that DNA, when attached to the cellular membrane in the sites of sphingosine localization, becomes locally unwound. This should be taken into account in studying enzymatic reactions on membranes with participation of DNA.