Abstract
AppA is a member of a sensor of blue light using FAD (BLUF) protein family. In this study, effects of W104A mutation on spectroscopic properties of the AppA BLUF domain (AppA126) were investigated. The W104A mutant showed a nearly normal redshift in the UV-visible absorption of FAD upon illumination. However, the light state as revealed by the upshifted absorption relaxed to the dark state at a rate 150 times faster in the mutant than in the wild-type AppA126. The mutation led to 2cm-1 upshift of the C4=O stretch bands in the light-induced Fourier transform infrared (FTIR) spectrum. Notably, prominent protein bands assigned to the light-induced change of the β-sheet structure were markedly affected by the mutation to be eliminated and/or modified. These results indicate that Trp104 is responsible for transforming the light signal into a specific β-sheet structure change for the signaling state in the apoprotein of AppA BLUF domain.
