Electron transfer chemistry between DNA and DNA-binding tripeptides.
A DNA system consisting of pyrene-modified oligonucleotides and nitrobenzoate (Nb)-modified DNA-binding tripeptides has been applied to study electron-transfer processes through the DNA-peptide interface. 5-(Pyren-1-yl)-2'-deoxyuridine (Py-dU) has been used as the photoinducible charge generator. Upon excitation at 350 nm, a pyrene-like excited state (Py-dU) is formed which undergoes an electron transfer yielding the charge-separated state which is the contact ion pair Py(*)(+)-dU(*)(-). The subsequent electron shift from dU(*)(-) into the base stack competes with charge recombination and can be probed chemically by trapping the electron at the 5-bromo-2'-deoxyuridine (Br-dU) group leading to strand cleavage which can be quantified by HPLC analysis. Several Nb-modified DNA-binding tripeptides influence these DNA-mediated electron-transfer processes as shown by fluorescence spectroscopy experiments. Fluorescence quenching can occur primarily through a reductive electron-transfer process in which the Nb group traps the electron thermodynamically from the contact ion pair Py(*)(+)-dU(*)(-). Moreover, our results indicate that, once the negative charge has been trapped on the peptide, oxidative processes from Py(*)(+) take place resulting in an enhanced and nonspecific strand degradation of the Py-dU-modified duplexes. The latter type of strand cleavage can be inhibited by the presence of tryptophane or tyrosine as part of the peptides. Most remarkably, DNA-binding tripeptides, which bear both the Nb and the tryptophan/tyrosine moiety, are able to trap both the negative and the positive charge from the contact ion pair Py(*)(+)-dU(*)(-).
Mayer-Enthart
Elke
E
Chemistry Department, Technical University of Munich, Lichtenbergstr. 4, D-85747 Garching, Germany.
Kaden
Peter
P
Wagenknecht
Hans-Achim
HA
D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D003857:Deoxyuridine / Q000031:analogs & derivatives* / Q000737:chemistry; D004579:Electron Transport; D005453:Fluorescence; D009579:Nitrobenzoates / Q000737:chemistry; D009842:Oligopeptides / Q000737:chemistry*; D011721:Pyrenes / Q000737:chemistry*
C505579:5-(pyren-1-yl)-2'-deoxyuridine; D009579:Nitrobenzoates; D009842:Oligopeptides; D011721:Pyrenes; D004247:DNA; D003857:Deoxyuridine