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 ?-FAD, respectively) were used to reconstitute apo-PL, giving e-PL and ?-PL respectively. The reconstitution yield of e-PL was very poor, suggesting that the hydrophobicity of the ethano group prevented its uptake, while ?-PL showed 50% reconstitution yield. The substrate binding constants for ?-PL and rPL were identical. ?-PL showed a 15% higher steady-state repair yield compared to FAD-reconstituted photolyase (rPL). The acceleration of repair in ?-PL is discussed in terms of an ?-Ade radical intermediate vs superexchange mechanism.

SUBMITTER: Narayanan M 

PROVIDER: S-EPMC7350397 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature