Photolyases

Cryptochrome/photolyases, a special group of enzymes(flavoproteins), use the blue spectral range of visible light to
repairtwo types of
UV-identified DNA light damage: a cyclobutane-pyrimidine dimer (CPD) and a pyrimidine-pyrimidone(6-4) photoproduct (6-4PP). Crypotchoma acts as a photoreceptor.

Photolyases are enzymes (lyases) that repair UV-induced DNA damage in bacteria, for example (in higher mammals, especially in humans, functional photolyases are missing). Photolyases use light energy (UV and short-wave visible light) to reverse the UV-induced pathological linkages of pyrimidine bases.

In photolyases, a so-called antenna chromophore absorbs the light energy required for the repair process. This absorbed energy is transferred to a reduced redox cofactor - adenine dinucleotide (FAD) - which is responsible for the actual chemical reaction. From the redox system, an electron jumps to the DNA damage in the active centre, which is then dissolved. The flavin is then returned to its reduced, initial state by an electron transfer from a tryptophan on the enzyme surface. In contrast to other repair mechanisms, the correction takes place without cutting the DNA.

Eryfotona®

Note: Photolyase-containing preparations have recently appeared on the market and are used together with a sunscreen preparation for mild actinic keratoses (Eryfotona®).

1. Fortunato AE et al (2015) Dealing with light: the widespread and multitasking cryptochrome/photolyase family in photosynthetic organisms. J Plant Physiol 172:42-54.
2. Liu Z et al. (2015) Dynamics and mechanisms of DNA repair by photolyase. Phys Chem Chem Phys 17:11933-11949.
3. Yokoyama H et al (2014) Structural biology of DNA (6-4) photoproducts formed by ultraviolet radiation and interactions with their binding proteins. Int J Mol Sci 15: 20321-20328.
4. Zhong D (2015) Electron transfer mechanisms of DNA repair by photolyase. Annu Rev Phys Chem 66:691-715.