Design, synthesis, and evaluation of a biomimetic artificial photolyase model

Selective Alkylation of C-Rich Bulge Motifs in Nucleic Acids by Quinone Methide Derivatives

A quinone methide precursor featuring a bis-cyclen anchoring moiety has been synthesized and its capacity to alkylate oligonucleotide targets quantified in the presence and absence of divalent metal ions (Zn(2+) , Ni(2+) and Cd(2+) ). The oligonucleotides were designed for testing the sequence and secondary structure specificity of the reaction. Gel electrophoretic analysis revealed predominant alkylation of C-rich bulges, regardless of the presence of divalent metal ions or even the bis-cyclen anchor. This C-selectivity appears to be an intrinsic property of the quinone methide electrophile as reflected by its reaction with an equimolar mixture of the 2'-deoxynucleosides. Only dA-N1 and dC-N3 alkylation products were detected initially and only the dC adduct persisted for detection under conditions of the gel electrophoretic analysis.

Synthesis of rigidified flavin-guanidinium ion conjugates and investigation of their photocatalytic properties

Flavin chromophores can mediate redox reactions upon irradiation by blue light. In an attempt to increase their catalytic efficacy, flavin derivatives bearing a guanidinium ion as oxoanion binding site were prepared. Chromophore and substrate binding site are linked by a rigid Kemp's acid structure. The molecular structure of the new flavins was confirmed by an X-ray structure analysis and their photocatalytic activity was investigated in benzyl ester cleavage, nitroarene reduction and a Diels-Alder reaction. The modified flavins photocatalyze the reactions, but the introduced substrate binding site does not enhance their performance.

Do photolyases need to provide considerable activation energy for the splitting of cyclobutane pyrimidine dimer radical anions?

cis-syn Cyclobutane pyrimidine dimers, major UV-induced DNA lesions, are efficiently repaired by DNA photolyases. The key step of the repair reaction is a light-driven electron transfer from the FADH(-) cofactor to the dimer; the resulting radical anion splits spontaneously. Whether the splitting reaction requires considerable activation energy is still under dispute. Recent reports show that the splitting reaction of a dimer radical anion has a significant activation barrier (0.45 eV), and so photolyases have to provide considerable energy. However, these results contradict observations that cis-syn dimer radical anions split into monomers at -196 degrees C, and that the full process of DNA photoreactivation was fast (1.5-2 ns). To investigate the activation energies of dimer radical anions, three model compounds 1-3 were prepared. These include a covalently linked cyclobutane thymine dimer and a tryptophan residue (1) or a flavin unit (3), and the covalently linked uracil dimer and tryptophan (2). Their properties of photosensitised splitting of the dimer units by tryptophan or flavin unit were investigated over a large temperature range, -196 to 70 degrees C. The activation energies were obtained from the temperature dependency of splitting reactions for 1 and 2, 1.9 kJ mol(-1) and 0.9 kJ mol(-1) for the thymine and uracil dimer radical anions, respectively. These values are much lower than that obtained for E. coli photolyase (0.45 eV), and are surmountable at -196 degrees C. The activation energies provide support for previous observations that repair efficiencies for uracil dimers are higher than thymine dimers, both in enzymatic and model systems. The mechanisms of highly efficient enzymatic DNA repair are discussed.

Effective Methods for the Biotinylation of Azamacrocycles

The biotin-(strept)avidin interaction remains a gold standard of model biological recognition events. The biotinylation of azamacrocycles permits the investigation of signal transduction between this recognition event and the metal center of an azamacrocycle complex, of wide potential interest in biosensing. There are no generally applicable procedures in the literature for such functionalizations. We report here a comprehensive investigation into the attachment of biotin to TACN, cyclen, and cyclam. Effective methods have been found for each ring. The efficacy of the functionalization is critically dependent on the nature of the azamacrocycle.

Efficient cycloreversion of cis,syn-thymine photodimer by a Zn2+–1,4,7,10-tetraazacyclododecane complex bearing a lumiflavin and tryptophan by chemical reduction and photoreduction of a lumiflavin unit

DNA photolyases (EC 4.1.99.3) are enzymes that catalyze photoreversion of cis,syn-thymine photodimer (T[c,s]T), which is one of major photolesion products in DNA, by utilizing UV light. In this work, we have designed and synthesized Zn2+ -1,4,7,10-tetraazacyclododecane complexes bearing a lumiflavin and L: -tryptophan (ZnL3) or L: -phenylalanine (ZnL4) as artificial DNA photolyases. We have found that (ZnL3)red, whose flavin unit was reduced in situ by Na2S2O4, accelerates the photoreversion of T[c,s]T utilizing near-UV light in aqueous solution at pH 7.6 and 11. Interestingly, more efficient photoreversion of T[c,s]T was achieved by UV irradiation of an oxidized form of ZnL3 [(ZnL3)ox] in the presence of an excess amount of Et3N at pH 11. UV-vis and fluorescence measurements and action spectra showed that an oxidized form of flavin of (ZnL3)ox was photoreduced by Et3N into its reduced form (ZnL3)red, which promoted the photoreduction of T[c,s]T. Comparison of the photochemical properties of ZnL3 with those of ZnL4 suggested that a tryptophan unit in ZnL3 contributed to the stabilities of the flavin through intramolecular photoinduced electron transfer.

Efficient photosensitized splitting of the thymine dimer/oxetane unit on its modifying beta-cyclodextrin by a binding electron donor

Two modified beta-cyclodextrins (beta-CDs) with a thymine dimer and a thymine oxetane adduct respectively, TD-CD and Ox-CD, have been prepared, and utilized to bind an electron-rich chromophore, indole or N,N-dimethylaniline (DMA), to form a supramolecular complex. We have examined the photosensitized splitting of the dimer/oxetane unit in TD-CD/Ox-CD by indole or DMA via an electron-transfer pathway, and observed high splitting efficiencies of the dimer/oxetane unit. On the basis of measurements of fluorescence spectra and splitting quantum yields, it is suggested that the splitting reaction occurs in a supramolecular complex by an inclusion interaction between the modified beta-CDs and DMA or indole. The back electron transfer, which leads low splitting efficiencies for the covalently-linked chromophore-dimer/oxetane compounds, is suppressed in the non-covalently-bound complex, and the mechanism has been discussed.