The highly effective anticancer drug cisplatin, cis-[Pt(NH3)2Cl2], induces a structural change in deoxyribonucleic acid (DNA) upon binding. This cisplatin-induced alteration in DNA conformation is recognized by a family of cellular proteins that contain a homologous 80 amino acid sequence known as the HMG domain. Binding of cisplatin-modified DNA by such proteins may have major implications for the molecular mechanism of this anticancer drug and optimization of this binding interaction may lead to the development of more effective anticancer treatments. The specific objective of this project is to determine the three-dimensional structure of the complex formed by cisplatin-modified DNA and the HMG domain. The second HMG domain from rat HMG1 protein (K86-K165, HMGdomB) (G. Paonessa, R. Frank, and R. Cortese, Nuc. Acids Res. 15, 9077 (1987)) has been expressed in Escherichia coli and isotopically enriched (99.9% 15N) by growth on a minimal medium containing 15NH4Cl as the sole source of nitrogen. Gel mobility shift assays performed in our laboratory have shown that this domain binds specifically (Kd & 10-6 M) to cisplatin-modified oligonucleotides having as few as 15-20 base pairs. A series of NMR spectra have been collected at 501.7 MHz (1H) on this protein (3 mM in 100 mM KCl, 0.1 mM EDTA, 10 mM sodium phosphate, pH 6.6, 10% D2O, at 293 K) in order to begin assigning the resonances of this 80 amino acid binding domain. These spectra include a 3D 1H nuclear Overhauser enhancement 15N-1H heteronuclear multiple quantum coherence (NOESY-HMQC) experiment with a mixing time of 200 ms, a 2D 1H-15N heteronuclear single quantum coherence (HSQC) spectrum, and 2D 1H NOESY spectra with mixing times of 100 ms and 200 ms. Preliminary NMR titration experiments with HMGdomB and cisplatin-modified oligonucleotides are currently in progress.
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