title: Characterization of the subdomains in the N-terminal region of histidine kinase Hik33 in the cyanobacterium Synechocystis sp. PCC 6803.
abstract: Histidine kinase Hik33 responds to a variety of stress conditions and regulates the expression of stress-inducible genes in the cyanobacterium Synechocystis sp. PCC 6803. However, the mechanisms of response and regulation remain unknown. Generally, a histidine kinase perceives a specific signal via its N-terminal region. Hik33 has two transmembrane helices, a periplasmic loop, and HAMP and PAS domains in its N-terminal region, all of which might be involved in signal perception. To investigate the functions of these subdomains in vivo, we expressed a chimeric histidine kinase (Hik33n-SphSc) by fusing the N-terminal region of Hik33 with the C-terminal region of a sensory histidine kinase that is activated under phosphate-deficient conditions, SphS. Hik33n-SphSc responded to several stimuli that are perceived by intact Hik33 and regulated expression of the phoA gene for alkaline phosphatase, which is normally regulated under phosphate-deficient conditions by SphS. We introduced genes for modified versions of Hik33n-SphSc into Synechocystis and monitored expression of phoA under standard and stress conditions. Hik33n-SphSc lacking either the transmembrane helices or both the HAMP and PAS domains had no kinase activity, whereas Hik33n-SphSc lacking the HAMP or the PAS domain enhanced expression of phoA. Moreover, variants of Hik33n-SphSc, in which the membrane-localizing region was replaced by those of other histidine kinases, also responded to stress conditions. Thus, transmembrane helices, regardless of sequence, appear to be essential for the function of Hik33, while the HAMP and PAS domains play important roles in regulating kinase activity in vivo.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Shimura
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shiraiwa
authors.forename: Iwane
authors.initials: I
authors.lastname: Suzuki
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015152:Blotting, Northern; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D057075:Enzyme Assays; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D000071677:Histidine Kinase; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D011494:Protein Kinases; C116037:PAS domain kinases; D017346:Protein Serine-Threonine Kinases; D000071677:Histidine Kinase; D000469:Alkaline Phosphatase