Abstract
Synechocystis sp. PCC 6803 has been a model organism for molecular analysis of genes involved in such photoresponses. We have shown that SyPixJ1 is blue light receptor essential for positive phototaxis in Synechocystis. Previously, we reported properties of TePixJ_GAF. of T. elongatus that is homologous to the chromophore-binding domain of SyPixJ1. We expressed TePixJ_GAF with a His tag in Synechocystis. Purified TePixJ_GAF showed reversible photoconversion between the 430 nm and 530 nm-absorbing forms which is very similar to SyPixJ1. Here, we report detailed analysis of TePixJ_GAF. We identified a peptide fragment that binds the chromophore by using MALDI/TOFMS. Either spectral form of TePixJ_GAF did not show spontaneous dark reversion. Denaturation of TePixJ_GAF showed that the bound chromophore is significantly different from phycocyanobilin of phycocyanin. Therefore we suggested that structure and binding site of the chromoophore in TePixJ and SyPixJ1 are unique in comparison with plant phytochorome and bacteriophytochrome.
