Crystal Structure of Synechococcus Elongatus 6-4 Photolyase Suggests a Novel Repairing Mechanism

Se PhrB provides the first structure of prokaryotic 6 − 4 photolyases with 8-HDF as the antenna cofactor, and also the first structure of photolyases with covalently-linked FAD as the catalytic cofactor. It also contains a [4Fe-4S] cluster coordinated with four conserved cysteine residues. Based on the structural analysis and the inspiration of a study on human primase 27 , we propose that the [4Fe-4S] cluster in Se PhrB may participate in electron transfer and trigger DNA disassociation during catalysis. The binding sites for 8-HDF in Se PhrB and for 8-HDF, DMRL, FMN, or FAD in other photolyases are in homologous positions, which suggests that 8-HDF may be utilized as the antenna cofactor by the last common ancestor of the antenna cofactor-containing photolyases. The formation of the covalent linkage between FAD and Met399 in Se PhrB is light-dependent, which does not require external electron donors. The FAD-methionine photo-adduct in Se PhrB is catalytically proficient and stable under aerobic conditions. The novel findings from Se PhrB suggest that photolyase family is more complex than expected, which warrant further intensive investigation.