Before and after: Crystal structures of the DNA (6‐4) photolyase from D. melanogaster—one structure in complex with DNA containing a (6‐4) lesion (see picture) and one in which the lesion has been repaired—provide new insight into lesion recognition and repair. The proposed mechanism for light‐induced, electron‐transfer‐based repair of the (6‐4) lesion does not proceed via an oxetane intermediate.
UV-light irradiation induces the formation of highly mutagenic lesions in DNA, such as cis-syn cyclobutane pyrimidine dimers (CPD photoproducts), pyrimidine(6-4)pyrimidone photoproducts ((6-4) photoproducts) and their Dewar valence isomers ((Dew) photoproducts). Here we describe the synthesis of defined DNA strands containing these lesions by direct irradiation. We show that all lesions are efficiently repaired except for the T(Dew)T lesion, which cannot be cleaved by the repair enzyme under our conditions. A crystal structure of a T(6-4)C lesion containing DNA duplex in complex with the (6-4) photolyase from Drosophila melanogaster provides insight into the molecular recognition event of a cytosine derived photolesion for the first time. In light of the previously postulated repair mechanism, which involves rearrangement of the (6-4) lesions into strained four-membered ring repair intermediates, it is surprising that the not rearranged T(6-4)C lesion is observed in the active site. The structure, therefore, provides additional support for the newly postulated repair mechanism that avoids this rearrangement step and argues for a direct electron injection into the lesion as the first step of the repair reaction performed by (6-4) DNA photolyases.
The importance of a backbone: The mechanism of formation of Dewar lesions has been investigated by using femtosecond IR spectroscopy and ab initio calculations of the exited state. The 4π electrocyclization is rather slow, occurs with an unusual high quantum yield, and--surprisingly--is controlled by the phosphate backbone.
This study reveals the molecular mechanism by which the nucleotide excision repair protein DDB2 prioritises excision of UV-induced DNA lesions in the nucleosome landscape.
Archae possess unique biochemical systems quite distinct from the pathways present in eukaryotes and eubacteria. 7,8-Dimethyl-8-hydroxy-5deazaflavin (F 0) and F420 are unique deazaflavin-containing coenzyme and methanogenic signature molecules, essential for a variety of biochemical transformations associated with methane biosynthesis and light-dependent DNA repair. The deazaflavin cofactor system functions during methane biosynthesis as a lowpotential hydrid shuttle F 420/F420H2. In DNA photolyase repair proteins, the deazaflavin cofactor is in the deprotonated state active as a light-collecting energy transfer pigment. As such, it converts blue sunlight into energy used by the proteins to drive an essential repair process. Analysis of a eukaryotic (6-4) DNA photolyase from Drosophila melanogaster revealed a binding pocket, which tightly binds F 0. Residues in the pocket activate the cofactor by deprotonation so that light absorption and energy transfer are switched on. The crystal structure of F0 in complex with the D. melanogaster protein shows the atomic details of F0 binding and activation, allowing characterization of the residues involved in F0 activation. The results show that the F0/F420 coenzyme system, so far believed to be strictly limited to the archael kingdom of life, is far more widespread than anticipated. Analysis of a D. melanogaster extract and of a DNA photolyase from the primitive eukaryote Ostreococcus tauri provided direct proof for the presence of the F0 cofactor also in higher eukaryotes.crystal structure ͉ deazaflavin ͉ DNA photolesion ͉ DNA repair ͉ photolyase
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.