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 (k ) 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.

Determinants of Photolyase’s DNA Repair Mechanism in Mesophiles and Extremophiles

“…30 However, the change in local environment that is produced by the DNA presence may influence, both geometrically and energetically, a potential ET step from the flavin to the adenine. Furthermore, recent experiments, using photolyases with adenine-modified FAD, 31 support the possible occurrence of two-step hopping, but a radical anion intermediate of the modified adenine was not observed. Electronic structure calculations by Weber et al found that the protein environment surrounding the FADH anion favors strong electronic overlap between the flavin radical and the adenine moiety 32 (and therefore a large electronic coupling between them 33 ).…”

Thiophene-fused boron dipyrromethenes as energy efficient near-infrared photocatalysts for radical polymerizations

“…S10 †), which were selected as effective co-initiators based on our prior reports. 14,25 A Rehm-Weller analysis 34 was performed to identify the most likely mechanism for photoredox catalysis with the present 3-component system. Excited-state oxidation (E * ox ) and reduction (E * red ) potentials for the thiophene-fused BODIPYs were estimated using the singlet excited state energy, E S1 , calculated from the crossover in absorption and uorescence (emission) proles, in combination with ground state redox potentials obtained from cyclic voltammetry (Table 1 and Fig.…”

Measuring electronic structure properties of flavins and flavoproteins by electronic Stark spectroscopy

“…For the past 20 years, we have been focused on the light-driven function of photoflavoproteins (Gindt et al, 2016;Kodali, Siddiqui, & Stanley, 2009;Lee, Kodali, Stanley, & Matsika, 2016;MacFarlane IV & Stanley, 2001Narayanan, Singh, Kodali, Moravcevic, & Stanley, 2017;Pauszek, Kodali, Siddiqui, & Stanley, 2011Stanley & MacFarlane IV, 2000), and flavin dyads Yu et al, 2012). In either case, it is not the ground state electronic structure that is of interest but, rather, the excited electronic states.…”