| FAD binding domain of DNA photolyase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| A deazaflavin photolyase from Anacystis nidulans, illustrating the two light-harvesting cofactors: FADH- (yellow) and 8-HDF (cyan). | |||||||||
| Identifiers | |||||||||
| Symbol | FAD_binding_7 | ||||||||
| Pfam | PF03441 | ||||||||
| InterPro | IPR005101 | ||||||||
| PROSITE | PDOC00331 | ||||||||
| SCOP | 1qnf | ||||||||
|
|||||||||
Photolyases (EC 4.1.99.3) are DNA repair enzymes that repair damage caused by exposure to ultraviolet light. This enzyme mechanism requires visible light, preferentially from the violet/blue end of the spectrum, and is known as photoreactivation.
Photolyase is a phylogenetically old enzyme which is present and functional in many species, from the bacteria to the fungi to the animals.[1] However it is no longer working in humans and other placental mammals who instead rely on the less efficient nucleotide excision repair mechanism.[2]
Photolyases bind complementary DNA strands and break certain types of pyrimidine dimers that arise when a pair of thymine or cytosine bases on the same strand of DNA become covalently linked. These dimers result in a 'bulge' of the DNA structure, referred to as a lesion. The more common covalent linkage involves the formation of a cyclobutane bridge. Photolyases have a high affinity for these lesions and reversibly bind and convert them back to the original bases.
Photolyases are flavoproteins and contain two light-harvesting cofactors. All photolyases contain the two-electron-reduced FADH-; they are divided into two main classes based on the second cofactor, which may be either the pterin methenyltetrahydrofolate (MTHF) in folate photolyases or the deazaflavin 8-hydroxy-7,8-didemethyl-5-deazariboflavin (8-HDF) in deazaflavin photolyases. Although only FAD is required for catalytic activity, the second cofactor significantly accelerates reaction rate in low-light conditions. The enzyme acts by electron transfer in which the reduced flavin FADH- is activated by light energy and acts as an electron donor to break the pyrimidine dimer.[3]
On the basis of sequence similarities DNA photolyases can be grouped into two classes. The first class contains enzymes from Gram-negative and Gram-positive bacteria, the halophilic archaebacteria Halobacterium halobium, fungi and plants. Proteins containing this domain also include Arabidopsis thaliana cryptochromes 1 and 2, which are blue light photoreceptors that mediate blue light-induced gene expression and modulation of circadian rhythms.
Some sunscreens include photolyase in their ingredients, claiming a reparative action on UV-damaged skin.[4]
|
|||||||||||||||||