Abstract
In the cyanobacterium Synechocystis sp. PCC 6803, we identified that one of the histidine kinase, Hik33, responds to multiple stimuli, such as cold, salt, hyperosmotic, and oxidative stress. Recently, it was reported that a novel protein, SipA interacts with a homolog of Hik33, NblS, from the cyanobacterium Synechococcus sp. PCC 7942.
In this study we examined biochemical functions of Hik33 and Ssl3451, which is a homolog of SipA from Synechocystis. The purified Ssl3451 dramatically enhanced the activity of autophosphorylation of Hik33 in vitro. We substituted the highly conserved hydrophilic amino acid residues among the homologous proteins from cyanobacteria and higher plants with alanine. The modified Ssl3451 dramatically decreased the ability of activation of Hik33, suggesting that these residues in Ssl3451 might have important functions to activate Hik33. We also analyzed phenotypes of a strain in which the ssl3451 gene was disrupted and will discuss roles of the protein in vivo.
