The archaeal cofactor F0 is a light-harvesting antenna chromophore in eukaryotes

Archae possess unique biochemical systems quite distinct from the pathways present in eukaryotes and eubacteria. 7,8-Dimethyl-8-hydroxy-5deazaflavin (F₀) and F₄₂₀ are unique deazaflavin-containing coenzyme and methanogenic signature molecules, essential for a variety of biochemical transformations associated with methane biosynthesis and light-dependent DNA repair. The deazaflavin cofactor system functions during methane biosynthesis as a low-potential hydrid shuttle F₄₂₀/F₄₂₀H₂. In DNA photolyase repair proteins, the deazaflavin cofactor is in the deprotonated state active as a light-collecting energy transfer pigment. As such, it converts blue sunlight into energy used by the proteins to drive an essential repair process. Analysis of a eukaryotic (6-4) DNA photolyase from Drosophila melanogaster revealed a binding pocket, which tightly binds F₀. Residues in the pocket activate the cofactor by deprotonation so that light absorption and energy transfer are switched on. The crystal structure of F ₀ in complex with the D. melanogaster protein shows the atomic details of F₀ binding and activation, allowing characterization of the residues involved in F₀ activation. The results show that the F₀/F₄₂₀ coenzyme system, so far believed to be strictly limited to the archael kingdom of life, is far more widespread than anticipated. Analysis of a D. melanogaster extract and of a DNA photolyase from the primitive eukaryote Ostreococcus tauri provided direct proof for the presence of the F₀ cofactor also in higher eukaryotes.