Crystal structure of Synechococcus elongatus 6-4 photolyase suggests a novel repairing mechanism

Abstract

SePhrB 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 primase27, we propose that the [4Fe-4S] cluster in SePhrB may participate in electron transfer and trigger DNA disassociation during catalysis. The binding sites for 8-HDF in SePhrB 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 SePhrB is light-dependent, which does not require external electron donors. The FAD-methionine photo-adduct in SePhrB is catalytically proficient and stable under aerobic conditions. The novel findings from SePhrB suggest that photolyase family is more complex than expected, which warrant further intensive investigation.