Chapter 8. Blue Light-Initiated DNA Repair by Photolyase

In 1949 an enzyme was discovered that could repair UV-light-induced DNA lesions, by effectively reversing their formation with the aid of blue light. The class of enzymes has subsequently been named photolyases and the process, photoreactivation. All photolyases utilize a non-covalently bound cofactor, flavin adenine dinucleotide (FAD). With the exception of cryptochromes, with which photolyases share a high degree of structural homology in the N-terminal domain, photolyases show no similarity to other blue-light sensing flavoproteins, such as the phototropins or the recently discovered BLUF domains. Although, flavoproteins are ubiquitous, redox-active catalysts for one- and two-electron transfer reactions, it is the properties of the photoexcited states of the different redox states of FAD that are also important in photolyases. Two milestones mark the progress of photolyase research in recent years. The first was the elucidation of the three-dimensional structure of the enzyme in 1995 that revealed remarkable details, such as the FAD-cofactor arrangement in an unusual U-shaped configuration, and in late 2004 a structure was presented that included a bound fragment of repaired DNA. In the 10 years between, research on photolyases continued at a frenetic pace using all available biochemical and biophysical tools. This chapter focuses on recent biophysical studies and shows how different approaches have yielded details on the fundamental aspects of the modus operandi of this unique class of flavoenzymes.