Abstract
Illumination of Slr1694 protein, which has a novel FAD binding fold BLUF induced the changes in UV-Vis absorption , protein structure and FAD isoalloxazine ring at C4=O, C2=O, N1C10a and C4aN5 bonding. Furthermore, illumination induced changes in the state of weakly hydrogen bonded water molecules. The UV-Vis absorption change was normally induced when water content of the sample was reduced despite of somewhat reduced extent. Surprisingly, the structural changes of the protein, the FAD ring and water molecules disappeared at this condition with the exception of the change of FAD ring at C4=O, which was insensitive to reducing water content. Similar tendency was observed at lowering temperatures (- 30 C). The results indicate that the light-induced absorption change of FAD chromophore can be easily decoupled with the other light-induced structural changes, presumably due to disorder of water-involved hydrogen bonding networks in the protein.
