Structure and Function of Photolyase and in Vivo Enzymology: 50th Anniversary

Photoreactivation is the reversal of the harmful effects of far-UV radiation (200-300 nm) on organisms, such as growth delay, mutation, cell death, and cancer, by concomitant or subsequent exposure of the organism to near-UV/blue light (300-500 nm). The two major lesions induced in DNA by UV light are cyclobutane pyrimidine dimers (Pyr <> Pyr(2) or CPD), which constitute similar to 80-90% of the photoproducts, and pyrimidine-pyrimidone (6-4) photoproducts (Pyr[6-4] Pyr), which account for the 10-20% of the UV lesions. Photoreactivation results from the repair of these lesions in situ by flavoproteins called photoreactivating enzymes (photolyase) that use a blue-light photon as a co-substrate. Photolyases that repair these two photoproducts are evolutionarily related but functionally distinct. Enzymes that repair CPDs are referred to as CPD photolyase, and enzymes that repair (6-4) photoproducts are called (6-4) photolyase. For historical reasons and as a matter of common practice, the term photolyase without further qualification means CPD photolyase, and it will be used as such in this review, which celebrates the 50th anniversary of the discovery of photolyase.