Photoreactivity of platinum(II) in cisplatin-modified DNA affords specific cross-links to HMG domain proteins.
Cisplatin-modified DNA forms specific complexes with proteins that contain the DNA binding motif known as the high-mobility group (HMG) domain. As a tool for investigating the role of these proteins in mediating the cytotoxic effects of cisplatin, a set of cisplatin analogs was prepared in which one of the ammine ligands was replaced with a photoreactive tethered aryl azide ligand. The ability of DNA modified by these platinum complexes to photo-cross-link to HMG1 was investigated. During this study, it was discovered that DNA modified with cisplatin itself can undergo photoinduced cross-linking to HMG1 when irradiated with 300 nm light. The covalent complexes resulting from this latter cross-linking reaction are completely reversed by the addition of sodium cyanide and can be degraded by proteinase K. These results confirm the presence of a protein-DNA cross-link and demonstrate that the platinum atom itself forms the point of attachment. By contrast, DNA modified with transdiamminedichloroplatinum(II), [Pt(dien)Cl]Cl, or [Pt(NH3)3Cl]Cl does not cross-link to HMG1 upon irradiation. The photochemistry was exploited to cross-link a 15-base pair oligonucleotide containing a single, site-specific cis-[Pt(NH3)2{d(GpG)-N7(1),-N7(2)}] intrastrand adduct to domain B of HMG1. Following proteolytic digestion of the resulting covalent complex, the site of attachment to the protein was determined by Edman degradation of the resulting peptide-DNA complex to be a single residue on HMG domain B, Lys-6. The data further suggest that this amino acid binds to platinum at a site made available by photolabilization of a purine ligand. These results afford the first structural information about the interaction of HMG domain proteins with cisplatin-modified DNA.
Kane
S A
SA
Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139, USA.
Lippard
S J
SJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002945:Cisplatin / Q000737:chemistry*; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents; D018736:DNA Adducts / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics; D006609:High Mobility Group Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D009944:Organoplatinum Compounds / Q000737:chemistry*; D010777:Photochemistry; D051381:Rats; D014466:Ultraviolet Rays
D003432:Cross-Linking Reagents; D018736:DNA Adducts; D006609:High Mobility Group Proteins; D009838:Oligodeoxyribonucleotides; D009944:Organoplatinum Compounds; C057270:cisplatin-DNA adduct; D002945:Cisplatin