Abstract
In the cyanobacterium Synechocystis sp. PCC 6803, some histidine kinases (Hiks) have been identified as signal sensors. Among them, Hik33 has unique characteristics to respond to several independent stimuli, such as hyperosmotic, salt, cold and oxidative stress. Recently, using yeast two-hybrid screening an accessory protein, Ssl3451, which specifically interacts with the carboxyl-portion of Hik33, has been identified.
In the present study, a truncated form of Hik33, Hik33-c, in which the two transmembrane domains were eliminated, and a full-length Ssl3451 were overexpressed in the cell of Escherichia coli and subsequently both were purified. The purified Hik33-c protein was capable of autophosphorylation in vitro. Interestingly addition of the purified accessory protein to the reaction mixture enhanced the phosphorylation activity of Hik33-c. These results indicated that the accessory protein, Ssl3451, might be involved in regulation of Hik33. This is the first identification of a regulatory component for Hik.
