Abstract
AppA is a novel flavin-based blue-light photoreceptor controlling photosynthesis gene expression in the purple bacterium Rhodobacter sphaeroides. AppA is based on two domains: one is N-terminal flavin-binding domain named BLUF, and the other is C-terminal region where a transcriptional repressor PpsR could associate. Previous spectroscopic analyses have indicated that W104 is necessary for light-induced beta-sheet structural changes in AppA. To get more insight into the role of the amino acid, we biochemically characterized W104A mutant protein, and physiologically analyzed the mutant strain that harbors the W104A mutation on its genome. Obtained results indicated that W104A mutation causes loss of sensitivity of AppA to blue-light for controlling its in vivo and in vitro activity. Together with recent-solved structures of several BLUF proteins, mechanism of photocycle reaction of AppA will be discussed.
