Write the mechanism of CPD photolyases in repair of DNA-00202

CPD photolyase can bind to DNA in the dark by recognizing the altered DNA structure caused by a CPD formation rather than a specific nucleotide sequence.

This binding is about 10 5 tighter when a DNA segment contains a CPD than when it does not.

1. Half of the binding energy appears to come from interactions between enzyme and the DNA back bone.
2. The other half of energy comes from interactions between the FADH at the active site and the CPD.
3. However, the light harvesting antenna pigment does not influence binding.
4. Once the enzyme - DNA complex is formed, the CPD is flipped out of the DNA double helix and into the enzyme's active site.
5. After the CPD flips into the enzyme's active site, the energy of an absorbed photon is transferred from the light harvesting antenna pigment to the FADH
6. FADH then transfers an electron to the CPD to induce cyclobutane ring cleavage.
7. The catalytic cycle is completed when the electron is transferred back from the repaired thymine to the FADH cofactor.