Serial femtosecond crystallography and photolyase: in crystallo photoactivation and DNA repair
DNA-photolyases are light-driven, DNA repair enzymes which suffer in-situ photoreduction during X-ray crystallographic data collection. Accordingly, all known crystal structures present ill-defined reaction intermediates. By combining damage free serial femtosecond crystallography (DF-SFX), as performed at the SACLA facility, Japan, with other biophysical techniques, here we reveal the structural changes in the undistorted reaction steps of the photoreduction of a class II CPD DNA-photolyase, i.e. oxidized, semiquinone, and hydroquinone, both in the presence and absence of the DNA substrate. These address in detail the stabilization mechanism for the FAD co-factor in its different isoforms, how the protein moiety may lengthen one state’s half-life above the others, as well as insights into the mechanism of photoinduced DNA repair.
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