Photochemistry of CryB from Rhodobacter sphaeroides

In recent years, a distinct class of prokaryotic DNA photolyases containing a ribolumazine and an iron-sulfur cluster in addition to the catalytically active flavin adenine dinucleotide (FAD) cofactor has been identified: FeS-BCP. Previous studies of the structural, photochemical, enzymatic, and signaling properties have revealed photocatalytic and photoreceptor activities for the FeS-BCP subclade. These findings imply that FeS-BCP functions are coupled to the flavin redox state and modulated by the surrounding micro environment. Here, we employ various spectroscopic techniques to investigate the photochemistry of CryB from Rhodobacter sphaeroides. A combination of time-resolved and steady-state techniques allowed elucidation of the photocycle following light excitation on the nanosecond to minute timescale. An accelerated (<5 ns) deprotonation reaction of the terminal electron donor, tryptophan-338, in comparison to other photolyases and cryptochromes has been found with implications for both biological electron transfer and structure-function relationships while no direct involvement of the aforementioned secondary cofactors could be revealed. The obtained results are substantial for future studies of this distinct subclass and advance our understanding of flavoprotein photochemistry in general.