RESUMEN
Photolyases are ubiquitously occurring flavoproteins for catalyzing photo repair of UV-induced DNA damages. All photolyases described so far have a bilobal architecture with a C-terminal domain comprising flavin adenine dinucleotide (FAD) as catalytic cofactor and an N-terminal domain capable of harboring an additional antenna chromophore. Using sequence-similarity network analysis we discovered a novel subgroup of the photolyase/cryptochrome superfamily (PCSf), the NewPHLs. NewPHL occur in bacteria and have an inverted topology with an N-terminal catalytic domain and a C-terminal domain for sealing the FAD binding site from solvent access. By characterizing two NewPHL we show a photochemistry characteristic of other PCSf members as well as light-dependent repair of CPD lesions. Given their common specificity towards single-stranded DNA many bacterial species use NewPHL as a substitute for DASH-type photolyases. Given their simplified architecture and function we suggest that NewPHL are close to the evolutionary origin of the PCSf.
Asunto(s)
Criptocromos/genética , ADN de Cadena Simple/genética , Desoxirribodipirimidina Fotoliasa/genética , Secuencia de Aminoácidos/genética , Dominio Catalítico/genética , Dominio Catalítico/efectos de la radiación , Daño del ADN/efectos de la radiación , Reparación del ADN/efectos de la radiación , ADN de Cadena Simple/efectos de la radiación , Desoxirribodipirimidina Fotoliasa/efectos de la radiación , Methylobacterium/genética , Dímeros de Pirimidina/genética , Dímeros de Pirimidina/efectos de la radiación , Rhodobacteraceae/genética , Rayos UltravioletaRESUMEN
Cryptochromes and photolyases are blue-light photoreceptors and DNA-repair enzymes, respectively, with conserved domains and a common ancestry [1-3]. Photolyases use UV-A and blue light to repair lesions in DNA caused by UV radiation, photoreactivation, although cryptochromes have specialized roles ranging from the regulation of photomorphogenesis in plants, to clock function in animals [4-7]. A group of cryptochromes (cry-DASH) [8] from bacteria, plants, and animals has been shown to repair in vitro cyclobutane pyrimidine dimers (CPDs) in single-stranded DNA (ssDNA), but not in double-stranded DNA (dsDNA) [9]. Cry-DASH are evolutionary related to 6-4 photolyases and animal cryptochromes, but their biological role has remained elusive. The analysis of several crystal structures of members of the cryptochrome and photolyase family (CPF) allowed the identification of structural and functional similarities between photolyases and cryptochromes [8, 10-12] and led to the proposal that the absence of dsDNA repair activity in cry-DASH is due to the lack of an efficient flipping of the lesion into the catalytic pocket [13]. However, in the fungus Phycomyces blakesleeanus, cry-DASH has been shown to be capable of repairing CPD lesions in dsDNA as a bona fide photolyase [14]. Here, we show that cry-DASH of a related fungus, Mucor circinelloides, not only repairs CPDs in dsDNA in vitro but is the enzyme responsible for photoreactivation in vivo. A structural model of the M. circinelloides cry-DASH suggests that the capacity to repair lesions in dsDNA is an evolutionary adaptation from an ancestor that only had the capacity to repair lesions in ssDNA.
