Photochemistry, photophysics, and mechanism of pyrimidine dimer repair by DNA photolyase.
DNA photolyases photorepair pyrimidine dimers (Pyr < > Pyr) in DNA as well as RNA and thus reverse the harmful effects of UV-A (320-400 nm) and UV-B (280-320 nm) radiations. Photolyases from various organisms have been found to contain two noncovalently bound cofactors; one is a fully reduced flavin adenine dinucleotide (FADH-) and the other, commonly known as second chromophore, is either methenyltetrahydrofolate (MTHF) or 8-hydroxydeazaflavin (8-HDF). The second chromophore in photolyase is a light-harvesting molecule that absorbs mostly in the near-UV and visible wavelengths (300-500 nm) with its high extinction coefficient. The second chromophore then transfers its excitation energy to the FADH-. Subsequently, the photoexcited FADH- transfers an electron to the Pyr < > Pyr generating a dimer radical anion (Pyr < > Pyr.-) and a neutral flavin radical (FADH.). The Pyr < > Pyr.- is very unstable and undergoes spontaneous splitting followed by a back electron transfer to the FADH.. In addition to the main catalytic cofactor FADH-, a Trp (Trp277 in Escherichia coli) in apophotolyase, independent of other chromophores, also functions as a sensitizer to repair Pyr < > Pyr by direct electron transfer.
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Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599-7260.
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D001419:Bacteria / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000378:metabolism*; D010777:Photochemistry; D011740:Pyrimidine Dimers / Q000378:metabolism*; D014466:Ultraviolet Rays
D011740:Pyrimidine Dimers; D004247:DNA; D004255:Deoxyribodipyrimidine Photo-Lyase