Abstract
Cyanobacteria harbor many putative GAF-containing photoreceptors that may bind a linear tetrapyrrole as a chromophore (cyanobacteriochrome). Previously, we reported novel properties of a tetrapyrrole-binding GAF domain of TePixJ of Thermosynechococcus elongatus BP-1 that was expressed in Synechocystis. Purified protein showed reversible photoconversion between the 433nm and 531nm-absorbing forms. Molecular mass of the chromophore was identical to phycocyanobilin (PCB) but spectral properties were slightly different. Here, we report detailed denaturation analysis of TePixJ and Synechocystis phytochrome Cph1. After denaturation with acidic urea, both chromophores showed photoconversion without protein, however, the spectra of TePixJ chromophore were clearly different from those of Cph1 PCB. Global analysis of time-resolved spectral changes revealed several distinct intermediates in both pathways of photoconversion in TePixJ. These results suggested that the tetrapyrrole of TePixJ isomerizes between the ring C and D upon photoconversion like phytochrome but configuration in the other positions may be stereochemically distinct from each other.
