Abstract
AppA is a novel blue-light receptor controlling photosynthesis gene expression in purple bacteria.
The crystal structure of the light-sensing domain called BLUF shares some homology with acyl phosphatase. Other types of blue-light receptors, such as cryptochrome or phototropin, autophosphorylation is associated with their activity. These observations imply that BLUF also transmits a light signal through phosphorylation. Here we found that AppA BLUF domain has a light-dependent autophosphorylation activity. By the site-directed mutagenesis study, the phosphorylated residue was determined to be T30, and R32 was shown to assist the stability of the autophosphorylation reaction. A Q63L mutant protein lacking photo-cycle reaction lost the light dependence of the autophosphorylation reaction, indicating that the autophosphorylation activity is controlled by the light-dependent conformational change around Q63. We also showed that AppA regulates a sensor kinase activity through the phosphoryl-transfer reaction.
