title: An Ethenoadenine FAD Analog Accelerates UV Dimer Repair by DNA Photolyase.
abstract: Reduced anionic flavin adenine dinucleotide (FADH-) is the critical cofactor in DNA photolyase (PL) for the repair of cyclobutane pyrimidine dimers (CPD) in UV-damaged DNA. The initial step involves photoinduced electron transfer from *FADH-to the CPD. The adenine (Ade) moiety is nearly stacked with the flavin ring, an unusual conformation compared to other FAD-dependent proteins. The role of this proximity has not been unequivocally elucidated. Some studies suggest that Ade is a radical intermediate, but others conclude that Ade modulates the electron transfer rate constant (kET) through superexchange. No study has succeeded in removing or modifying this Ade to test these hypotheses. Here, FAD analogs containing either an ethano- or etheno-bridged Ade between the AN1 and AN6 atoms (e-FAD and ε-FAD, respectively) were used to reconstitute apo-PL, giving e-PL and ε-PL respectively. The reconstitution yield of e-PL was very poor, suggesting that the hydrophobicity of the ethano group prevented its uptake, while ε-PL showed 50% reconstitution yield. The substrate binding constants for ε-PL and rPL were identical. ε-PL showed a 15% higher steady-state repair yield compared to FAD-reconstituted photolyase (rPL). The acceleration of repair in ε-PL is discussed in terms of an ε-Ade radical intermediate vs superexchange mechanism.
authors.affiliation: Department of Natural Sciences, Mercy College, Dobbs Ferry, NY.
authors.forename: Madhavan
authors.initials: M
authors.lastname: Narayanan
authors.affiliation: Postdoctoral Fellow at the Department of Nanoscience and Engineering, Indian Institute of Science, Bangalore, India.
authors.forename: Vijay R
authors.initials: VR
authors.lastname: Singh
authors.affiliation: Merck & Co., Inc., West Point, PA.
authors.forename: Goutham
authors.initials: G
authors.lastname: Kodali
authors.affiliation: Large Molecule Analytical Development, Janssen Research & Development, LLC, Horsham, PA.
authors.forename: Katarina
authors.initials: K
authors.lastname: Moravcevic
authors.forename: Kimberly Jacoby
authors.initials: KJ
authors.lastname: Morris
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Stanley
mesh_terms: D000225:Adenine / Q000737:chemistry / Q000378:metabolism*; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000378:metabolism*; D019281:Dimerization; D004583:Electrons; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D011487:Protein Conformation; D011740:Pyrimidine Dimers / Q000378:metabolism*; D013379:Substrate Specificity; D014466:Ultraviolet Rays
chemical_list: D011740:Pyrimidine Dimers; D005182:Flavin-Adenine Dinucleotide; D004255:Deoxyribodipyrimidine Photo-Lyase; D000225:Adenine