2016
Volume 16, Number 1, pp. 65–69
The influence of porphyrins ZnTOEPyP4 and MnTOEPyP4 on the binding mode and conformation of A-RNA
J. Monaselidze, Sh. Gogichaishvili, M. Gorgoshidze, V. Bregadze, M. Kiladze, D. Khachidze, N. Gogelia, E. Lomidze and Sh. Barbakadze
E. Andronikashvili Institute of Physics, I. Javakhishvili Tbilisi State University, 6 Tamarashvili Street, 0177 Tbilisi, Georgia
CD and absorption spectra of the ZnTOEPyP4+A-RNA and MnTOEPyP4+A-RNA complexes and DSC of this porphyrin and the TOEPyP4+MnTOEPyP4 complexes have been studied. It was shown that, being an axial ligand, ZnTOEPyP4 is not able to intercalate between G–C pairs in the G–C-enriched region of A-RNA (rRNA) at a low concentration of ZnTOEPyP4. At high concentrations when the A-RNA chains are saturated, this porphyrin changes the conformation of the A-RNA duplex, so that intercalation of ZnTOEPyP4 between the G–C pairs becomes possible. MnTOEPyP4 binds externally only at moderate to high concentrations. Both porphyrins cause decreasing intensities of A-RNA’s own band at 260 nm and the negative band at 210 nm, and shifting of the proper band to longer wavelengths by 10 nm. This confirms that the transition of A-RNA to an A'-RNA-like conformation takes place and this transition has a noncoöperative character. DSC studies of dilute A-RNA solutions in 10 mM NaCI revealed a thermostable fraction melting at about 82 °C. At higher mixing ratios, the MnTOEPyP4+A-RNA complex sediments and melts as a highly ordered structure. We suppose that absence of influence of Zn and Mn on the CD spectra of these complexes is connected with conflict between the minor groove of A'-RNA and the size of the hydrated ions.
Keywords: absorption, A-RNA, A'-RNA, CD, DSC, porphyrin, rRNA+ channel