Complexation of the antibiotic daunomycin with desoxytetraribonucleoside triphosphate 5 '-d(CpGpCpG) in aqueous solution

This paper presents the results of our study, of the complexation of the an tibiotic daunomycin with desoxytetranucleotide 5'-d(CpGpCpG) in aqueous sal t solution by one- and two-dimensional (2D-TOCSY and 2D-NOESY) H-1 NMR spec troscopy (500 MHz). The concentration and temperature dependences of the pr oton chemical shifts of molecules were measured and used to calculate the e quilibrium reaction constants, the relative contents of different types of complex as functions of concentration and temperature, the limiting values of the proton chemical shifts of daunomycin in various complexes, and the t hermodynamic parameters of complexation Delta H and Delta S, It is conclude d that the triplet nucleotide sequences are the preferable sites at which d aunomycin is attached. The binding of the second daunomycin molecule to bot h single-stranded and duplex forms of tetramer is markedly anticooperative. This is explained by the presence in the antibiotic of a positively charge d amino sugar residue creating steric hindrances for the attachment of the second antibiotic molecule to the short tetranucleotide sequence. The most plausible spatial structure of the 1:2 complex of antibiotic with desoxytet ranucleotide is constructed using the calculated values of the induced prot on chemical shifts of daunomycin and 2D-NOE data.