Abstract
We studied the photoreaction of the BLUF domain of TePixD protein of Thermosynechococcus elongatus. The Tyr8 residue was modified to phenylalanine or alanine residues (Y8F or Y8A, respectively) by the site-directed mutagenesis. At room temperature, illumination induced the red shift of the absorption in the wild type (WT) protein, but not in the Y8F and Y8A mutant proteins as reported. However, the illumination at 80 K accumulated the red shifted forms both in the WT and mutant proteins. The illumination of Y8F protein at 80 K induced the red-shifted form to the extent at 1/2 of that in the WT protein at a 43 times slower rate. Upon the illumination at 150 K, the Y8F proteins did not accumulate the red-shifted forms, but accumulated the flavin anions. It is concluded that the photoconversion occurs even without Tyr8 residue, and that Tyr8 is necessary to enhance the photoconversion efficiency.
