Photoantenna in two cryptochrome–photolyase proteins from O. tauri: Presence, nature and ultrafast photoinduced dynamics

Abstract Cryptochromes and photolyases are homologous flavoproteins either involved in photosensory functions or in the photorepair of UV-damaged DNA. We report on the presence, nature and ultrafast photoinduced dynamics of a photoantenna in two recently discovered cryptochrome/photolyase proteins (OtCPF1, a (6-4) photolyase, and OtCPF2, a cryptochrome-DASH), coming from the green alga Ostreococcus tauri . Whereas OtCPF1 does not show any apparent photoantenna after purification, OtCPF2 is found to bind the folate MTHF. Resonance energy transfer, from MTHF to the flavin cofactor (FAD) of OtCPF2, was studied by femtosecond transient absorption spectroscopy. It takes place in 15 ps when FAD is oxidized and 100 ps when it is fully reduced. The intrinsic photophysics of MTHF in acidic solution was studied for comparison. Two decays in the sub-100 ps regime were tentatively attributed to the presence of two conformers or to a quenching mechanism involving large-amplitude motions of the 1,2,3,4-tetrahydropyraxine ring. On the other hand, the nature of the missing photoantenna of OtCFP1 was questioned by means of sequence alignment and homology modeling. We propose that the deazaflavin 8-HDF could be the photoantenna of OtCFP1 in vivo .