Analysis of ultrafast energy transfer processes in cryptochromes using transient two-dimensional spectroscopy techniques

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Cryptochromes are flavoproteins present in all kingdoms of life, which function as magnetoreceptors in insects and synchronize the circadian clock of plants with the external light-dark cycle. They are evolutionary related to DNA-repairing photolyases. Unlike these enzymes, cryptochromes only rarely bind an additional light harvesting pigment, a so called antenna chromophore, alongside the photoreactive flavin chromophore (FAD). In photolyases the energy transfer processes from the antenna pigment to the FAD have already been investigated thoroughly whereas in cryptochromes only little is known about the functionality and characteristics of these chromophores. Consequently, the aim of the proposed research project is to reveal differences and commonalities of the ultrafast energy transfer processes of different antenna chromophores in cryptochromes in order to disclose their relevance for the light response. The animal-like cryptochrome aCRY from the green alga Chlamydomonas reinhardtii is the only known cryptochrome not only responsive to blue but also to yellow and red light. So far, the red light response of the aCRY was investigated using aCRY only carrying FAD. It has been shown, however, that the antenna chromophore 8-hydroxydeazaflavin (8-HDF) binds to aCRY. Therefore, I would like to investigate the light response of the protein carrying both chromophores using ultrafast two-dimensional electronic spectroscopy in order to analyze the characteristics and dynamics of the energy transfer between the chromophores. Additionally, ultrafast two-dimensional electronic-vibrational spectroscopy might elucidate the influence of the antenna chromophore on the photoreaction in aCRY on a structural level as well as its role for the functionality of the protein in general. For comparison, the DASH cryptochrome CRY-DASH1 from the green alga Chlamydomonas reinhardtii will be included into the analysis. In contrast to aCRY, CRY-DASH1 binds the antenna 5,10-methenyltetrahydrofolate (MTHF) in addition to the flavin chromophore. The investigation of the energy transfer processes in CRY-DASH1 with two-dimensional electronic spectroscopy might help to resolve commonalities and differences on the level of energy transfer dynamics between 8-HDF and MTHF. The investigation of the light response in CRY-DASH1 with two-dimensional electronic-vibrational spectroscopy might allow the comparison of structural changes in CRY-DASH1 to the processes observed in aCRY. Therefore, the proposed experiments might elucidate the relevance of different antenna chromophores in different cryptochromes.