DNA-CARBOHYDRATE INTERACTION - THE EFFECTS OF MONOSACCHARIDES AND DISACCHARIDES ON THE SOLUTION STRUCTURE OF CALF-THYMUS DNA

We report the interaction of calf-thymus DNA with D-glucose, D-fructos e, D-galactose and sucrose in aqueous solution at physiological pH wit h sugar/DNA(P)(P = phosphate) molar ratios (r) of 1/10, 1/5, 1, 5 and 10. FTIR difference spectroscopy was used to characterize the nature o f sugar-DNA interaction and correlations between spectral changes and structural variations for both sugar and DNA complexes have been estab lished. FTIR difference spectroscopic results showed major sugar inter action (H-bonding) with the PO2 groups of the backbone at low sugar co ncentrations (r = 1/10 and 1/5). Such interaction was characterized by the shift and the intensity variations of the backbone PO2 antisymmet ric stretch at 1222 cm(-1), which resulted in a major helical stabilit y of DNA duplex. As sugar concentration increased, carbohydrate bindin g to DNA bases occurred. Evidence for this comes from major shiftings of the sugar O-H stretching vibrations at 3500-3200 cm(-1), and sugar C-O stretches and OH bending modes at 1450-1000 cm(-1). Similarly, shi fting and intensity variations of several DNA in-plane vibrations at 1 717 (G,T), 1663 (T,G,A,C) and 1492 cm(-1) (C,G) were observed, that ar e characterized by the presence of sugar-base interaction (via H2O). T he shiftings and the intensity changes of the sugar OH stretching mode s at 3500-3200 cm(-1) are also indicative of the rearrangements of the sugar intermolecular H-bonding network on DNA complex formation. A pa rtial B to A conformational transition was observed for DNA molecule o n sugar complexation, whereas carbohydrate binding occurred via both a lpha- and beta-anomeric structures.