Abstract
Cyanobacteria harbor many photoreceptors (cyanobacteriochromes) that bind a linear tetrapyrroles and respond to a wide range of lights. In this study, we characterized putative photoreceptor Tlr0924 of Thermosynechococcus elongatus. Tlr0924 has the chromophore-binding GAF domain and GGDEF domain that synthesizes cyclic dimeric guanosine monophosphate (c-di-GMP) as a second messenger. It was expected that the activity of Tlr0924 is regulated by light. We prepared full length of Tlr0924 protein, which was expressed in E. coli and Synechocystis. Purified proteins bound a tetrapyrrole chromophore and showed reversible photoconversion between blue light-absorbing form and green light-absorbing form. We measured the diguanylate cyclase activity as accumulation of the by-product pyrophosphate. Detection of c-di-GMP by mass spectrometry is now in progress. In addition, photoregulation of the diguanylate cyclase activity is now being measured. We are also trying to identify the phenotype of the tlr0924 disruptant under various light conditions.
