Biochemical characterization of the major adenylyl cyclase, Cya1, in the cyanobacterium Synechocystis sp. PCC 6803.

We report herein the biochemical properties of an adenylyl cyclase, Cya1, from the cyanobacterium Synechocystis sp. PCC 6803. Heterologously expressed Cya1 catalyzed cyclic AMP formation with a Km for ATP of approximately 2.2 microM at pH 7.5. Although cellular Cya1 activity is increased by blue light illumination [Terauchi and Ohmori, Mol. Microbiol. 52 (2004) 303], purified Cya1 did not contain any chromophores, and the activity was light-insensitive. This suggests that an unknown blue light-responsive factor interacts with the N-terminal regulatory domain of Cya1 to control its adenylyl cyclase activity. Finally, our results show that the sensor of blue light using FAD (BLUF) protein, Slr1694, does not appear to be involved in the regulation of Cya1-mediated cAMP signal transduction in this bacterium.