| Abstract: | A comparative study of the binding of square planar cis- and trans-Pt(NH3)2Cl2] complexes and the octahedral Ru(NH3)5(H2O)]3+ complex to tRNAphe from yeast was carried out by X-ray crystallography. Both of the carcinostatic compounds, cis-Pt(NH3)2Cl2] and Ru(NH3)5(H2O)]3+ show similarities in their mode of binding to tRNA. These complexes bind specifically to the N(7) positions of guanines G15 and G18 in the dihydrouridine loop. Ru(NH3)5(H2O)]3+ has an additional binding site at N(7) of residue G1 after extensive soaking times (58 days). A noncovalent binding site for ruthenium is also observed in the deep groove of the acceptor stem helix with shorter (25 days) soaking time. The major binding site for the inactive trans-Pt(NH3)Cl2] complex is at the N(1) position of residue A73, with minor trans-Pt binding sites at the N(7) positions of residues Gm34, G18 and G43. The similarities in the binding modes of cis-Pt(NH3)2Cl2] and Ru(NH3)5(H2O)]3+ are expected to be related to their carcinostatic properties. |
