Department of Chemistry, Graduate School of Science, Kyoto University^* National Institute of Advanced Industrial Science and Technology, Japan^** Department of Chemistry, Graduate School of Science, Kyoto University / RIKEN SPring-8 Center, Harima Institute, Japan^***
○Masahiro Fujihashi^* Nobutaka Numoto^* Kobayashi Yukiko^* Akira Mizushima^* Masaya Tsujimura^** Akira Nakamura^* Yutaka Kawarabayasi^** Kunio Miki^***

UV exposure on DNA molecules induces serious DNA lesions. CPD (cyclobutane pyrimidine dimer) photolyase repairs CPD type of lesion by using the energy of visible light. This enzyme possesses two chromophores; one catalyzes the CPD repair reaction and the other works as an antenna pigment that harvests photon energy. The catalytic cofactor of all known photolyases is FAD, whereas the light harvesting cofactor is either MTHF (5,10-methenyltetrahydrofolate) or 8-HDF (8-hydroxy-5-deaza-riboflavin). Three crystal structures of photolyases from E. coli, A. nidulans, and T. thermophilus have been determined; however, no archaeal photolyase structure is presently available. A similarity search of archaeal genomic data indicated the presence of a homologous gene, ST0889, on Sulfolobus tokodaii strain7. The crystal structure of the ST0889 protein is superimposed very well on the three known photolyase including the catalytic cofactor FAD, suggesting that the protein functions as a photolyase. Surprisingly, another FAD molecule is found at the position of the light harvesting cofactor. This second FAD is well accommodated in the crystal structure. Recent work indicates that FMN enhances Tt-photolyase activity. These facts suggest that FAD works as a novel light harvesting cofactor of photolyase. In addition, two of the four CPD recognition residues in the crystal structure of An-photolyase are not found in the ST0889 protein. An archaeal photolyase from S. tokodaii might utilize a different mechanism to recognize the CPD from that of An-photolyase.