Synthesis and characterization of a sequence-specific DNA-binding protein that contains ruthenium polypyridyl centers

A chimeric metallo-bZIP protein, (GBR-CC)Ru, was prepared that contains the native DNA-binding domain of the GCN-4 transcription factor (GBR), a synthetic α-helical coiled-coil dimerization site (CC), and a ruthenium polypyridyl complex (Ru) attached to a surface-exposed cysteine residue. The photophysical properties of the peptide-bound ruthenium complex include a long-lived emission that is shortened when the peptide is dissolved in air-saturated water. Electrophoretic mobility shift assays show that the chimeric metalloprotein also retains the essential DNA recognition properties of the native GCN-4 transcriptional activator. Peptide–DNA complexes are formed with the related AP1 and CRE sequences, but not the divergent Sp1 sequence. Peptide titration studies indicate that the affinities of (GBR-CC)Ru for the AP1 and CRE sites are comparable. Steady-state photolysis experiments show that (GBR-CC)Ru does not produce photoinduced DNA damage, probably due to the separation distance between the ruthenium sites and the DNA bases.