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Scientific result | Bacteria | Health ＆ life sciences
In collaboration with a German Research Team from Marburg University, Pavel Müller and Klaus Brettel (I2BC @ Saclay / SB2SM) have studied the first steps of photoactivation of a Class II photolyase of the Methanosarcina mazei archaeobacteria by resolute optical spectroscopy time and discovered a peculiarity of this class of photolyases: photoinduced separation of charges is stabilized by a water cluster, a structural element also preserved in class II photolyases of plants and animals.
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.
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P Müller, E Ignatz, S Kiontke, K Brettel, LO Essen. Sub-nanosecond tryptophan radical deprotonation mediated by a protein-bound water cluster in class II DNA photolyases (2018) Chem. Sci., 9, 1200-1212 http://dx.doi.org/10.1039/c7sc03969g
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