Cryptochromes and photolyases. The Ultra Violet powered protein family.

Photolyases and cryptochromes are evolutionarily related flavoproteins, which however perform distinct physiological functions. Photolyases (PHR) are evolutionarily ancient enzymes. They are activated by light and repair DNA damage caused by UV radiation. Although cryptochromes share structural similarity with DNA photolyases, they lack DNA repair activity. Cryptochrome (CRY) is one of the key elements of the circadian system in animals. In plants, CRY acts as a blue light receptor to entrain circadian rhythms, and mediates a variety of light responses, such as the regulation of flowering and seedling growth.

Cryptochromes are flavoproteins, which are homologous to photolyases but lack the DNA repair activity. Cryptochromes and photolyases have similar three-dimensional structures, characterized by an α/β domain and a helical domain. The structure also includes a chromophore, flavin adenine dinucleotide (FAD). The FAD-access cavity of the helical domain is the catalytic site of photolyases, and it is predicted also to be important in the mechanism of cryptochromes.

Despite the striking similarity between cryptochromes and photolyases, no photolyase activity of any kind has been observed in cryptochromes. Both uses UV radiation as a source of energy and FAD cofactor as antenna.

Cryptochromes also seem to be related also with magneto-reception in birds and other animals.

Cryptochrome compass radical mechaism mediated by UV light FAD antenna and trytophan residues y cry4 protein