Photocrosslinking between Peptide–Peptide or Peptide–Oligonucleotide by Ru^II–TAP Complexes

Abstract

Ru(II)-TAP complexes have been shown to be very attractive compounds in the frame of developments of new anticancer drugs targeting the genetic material. This increasing interest originates from observations of covalent bond formations, triggered by photo-induced electron transfer (PET) between Ru(II)-TAP complexes and guanine bases of DNA. This photoreaction has recently been extended to the tryptophan (Trp) amino acid for future applications involving peptides. Thus, a double photo-addition of Trp residues of peptides on Ru(II) complexes is demonstrated by mass spectrometry with some structural issues. Such bi-adduct formations offer the possibility of photocrosslinking two Trp-containing biomolecules, which is investigated in this study. Thus, photocrosslinking between two complementary oligonucleotides (ODNs) derivatized by Trp-containing tripeptides is demonstrated by polyacrylamide gel electrophoresis (PAGE) in the presence of Ru(II)-TAP complexes. Both PAGE and MS indicate that such photocrosslinkings arise from two reaction pathways: either via the double addition of Trp residues on the Ru complex or from dimerization of Trp radicals. The competition between these two pathways depends on the experimental conditions. Heterobridgings between guanine bases and tryptophan residues mediated by Ru(II)-TAP complexes is also examined, opening the way to ODN-peptide photocrosslinkings.

Photo-oxidizing RuII complexes and light: Targeting biomolecules via photoadditions

“…The yield of photocrosslinking increased from 0% (dark) to 41% (after 180 min irradiation) [85]. produces strong evidence for the formation of double photoadducts involving a Ru II complex and two Trp residues [92]. Indeed in addition to the already mentioned oxidized products of Trp, the presence of mono and double adduct species has been detected by mass spectrometry.…”

“…On the other hand, it was also observed that the luminescence of the same TAP-complexes is quenched by two amino acids, tryptophan (Trp) and tyrosine (Tyr) [85,91] with rate constants also close to the diffusion limit. When the Trp is included into a tripeptide for example, the quenching rate constant is modulated by the resulting charge of the peptide [92]. The transient species resulting from this quenching have also been kinetically studied under pulsed illumination in the nanosecond time domain.…”

“…The complex [Ru(TAP) 2 (phen)] 2+ and the tripeptide Lys-Trp-Lys have been attached on each strand of an ODN duplex which does not include any G base in its sequence (Fig. 15) [92]. Using this system ensures that the complex and the Trp are maintained close to each other.…”

“…Indeed, visible illumination of the system formed after hybridizing of one strand containing the Ru II complex and the complementary strand bearing the Trp, induces the appearance on the gel of a band corresponding to the crosslinking of the two strands. The use of a duplex as a matrix bearing the reactive species has also been applied to the study of the double photoreaction between the Ru II -TAP complex and two Trp residues [92].…”

“…18). Thus, a duplex of guanine-free ODN strands bearing each one a tripeptide Lys-Trp-Lys has been synthesized in order to investigate further the photoreaction between an unattached Ru II -TAP complex and two Trp residues in close proximity [92]. To help understanding the nature of the different photoproducts formed after visible illumination, the same system has been examined with [Ru(bpy) 3 ] 2+ .…”