The second chromophore in Drosophila photolyase/cryptochrome family photoreceptors.

The photolyase/cryptochrome family of proteins are FAD-containing flavoproteins which carry out blue-light-dependent functions including DNA repair, plant growth and development, and regulation of the circadian clock. In addition to FAD, many members of the family contain a second chromophore which functions as a photo-antenna, harvesting light and transferring the excitation energy to FAD and thus increasing the efficiency of the system. The second chromophore is methenyltetrahydrofolate (MTHF) in most photolyases characterized to date and FAD, FMN, or 5-deazariboflavin in others. To date, no second chromophore has been identified in cryptochromes. Drosophila contains three members of the cryptochrome/photolyase family: cyclobutane pyrimidine dimer (CPD) photolyase, (6-4) photoproduct photolyase, and cryptochrome. We developed an expression system capable of incorporating all known second chromophores into the cognate cryptochrome/photolyase family members. Using this system, we demonstrate that Drosophila CPD photolyase and (6-4) photolyase employ 5-deazariboflavin as their second chromophore, but Drosophila cryptochrome, which is evolutionarily closer to (6-4) photolyase than the CPD photolyase, lacks a second chromophore.