Abstract
Class II DNA photolyases are flavoenzymes occurring in both prokaryotes and eukaryotes including higher plants and animals. Despite considerable structural deviations from the well-studied class I DNA photolyases, they share the main biological function, namely light-driven repair of the most common UV-induced lesions in DNA, the cyclobutane pyrimidine dimers (CPDs). For DNA repair activity, photolyases require the fully reduced flavin adenine dinucleotide cofactor, FADH-, which can be obtained from oxidized or semi-reduced FAD by a process called photoactivation. Using transient absorption spectroscopy, we have examined the initial electron and proton transfer reactions leading to photoactivation of the class II DNA photolyase from Methanosarcina mazei. Upon photoexcitation, FAD is reduced via a distinct (class II-specific) chain of three tryptophans, giving rise to an FAD˙- TrpH˙+ radical pair. The distal Trp388H˙+ deprotonates to Trp388˙ in 350 ps, i.e., by three orders of magnitude faster than TrpH˙+ in aqueous solution or in any previously studied photolyase. We identified a class II-specific cluster of protein-bound water molecules ideally positioned to serve as the primary proton acceptor. The high rate of Trp388H˙+ deprotonation counters futile radical pair recombination and ensures efficient photoactivation.
Highlights
The exposure of DNA to UV light causes serious damage of the genetic code and eventually results in fatal mutations
Our transient absorption spectroscopic data have con rmed the functionality of the tryptophan cascade but they have brought about an additional issue: it turned out that upon electron transfer (ET) to the excited FADox, one of the oxidized tryptophans (TrpHc+) in the triad undergoes an unprecedentedly fast deprotonation, that is by three orders of magnitude faster than the terminal tryptophans in other PCSf proteins.[12,14,19]
Based on all the data obtained for WT and mutant proteins, we have constructed a reaction model (Scheme 1) of the primary processes following FADox photoexcitation in WT MmCPDII
Summary
The exposure of DNA to UV light causes serious damage of the genetic code and eventually results in fatal mutations. Compared to other members of the PCSf, the class II CPD photolyases, which occur in plants, animals and many microbial organisms, are highly divergent in terms of their sequences, especially in functionally important parts of the catalytic C-terminal domain.[4,5,6] Cryptochrome (Cry) blue light receptors of plants and animals evolved from class I CPD and (6-4) photolyases, respectively, but they have mostly lost the ability to repair DNA. They are involved in multiple light-regulation processes[3] and possibly in the light-dependent ‘magnetic compass’ of migrating birds and certain other animals.[7,8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
