Dynamic interplays between three redox cofactors in a DNA photolyase revealed by spectral decomposition.

DNA repair catalyzed by photolyases is accomplished by a light-dependent electron transfer event from a fully reduced flavin adenine dinucleotide to a DNA lesion site. Prokaryotic DNA photolyase, PhrB, possesses a ribolumazine cofactor and a four-iron-four-sulfur cluster in addition to the catalytic flavin, but their functional roles are poorly understood. Here, we employ time-resolved absorption spectroscopy to probe light-induced responses in both solution and single crystals of PhrB. We jointly analyze a large collection of light-induced difference spectra from the wild-type and mutant PhrB obtained under different light and redox conditions. By applying singular value decomposition to 159 time series, we dissect light-induced spectral changes and examine the dynamic interplay between three cofactors. Our findings suggest that these cofactors form an interdependent redox network to coordinate light-induced redox responses. We propose that the ribolumazine cofactor serves as a photoprotective pigment under intense light or prolonged illumination, while the iron-sulfur cluster acts as a transient electron cache to maintain balance between two otherwise independent photoreactions of the flavin and ribolumazine.