Functional analysis of the N-terminal region of an essential histidine kinase, Hik2, in the cyanobacteriumSynechocystissp. PCC 6803

Abstract

Histidine kinases are sensory proteins involved in the perception of environmental changes. Here, we characterized one of three essential histidine kinases, Hik2, in the cyanobacterium Synechocystis sp. PCC 6803 by constructing a fused sensor, Hik2n-Hik7c, which has the signal input domain of Hik2 and the kinase domain of the phosphate-deficiency sensor Hik7. The coding region of the hik7 gene was replaced with the fused sensor to evaluate the signalling activity in vivo as the activity of alkaline phosphatase (AP), which is regulated by Hik7. Cells expressing Hik2n-Hik7c had weak AP activities under standard growth conditions. Saline stress by NaCl induced AP activity in a dose-dependent manner. Analysis of the effects of several salt compounds on induction of AP activity indicated that Hik2n-Hik7c responded to Cl concentration. Amino acid substitution in the signal input domain of Hik2 resulted in loss of this responsiveness. These results suggest that the signal input domain of Hik2 responds to environmental Cl concentration in Synechocystis.

A Two-Component Regulatory System in Transcriptional Control of Photosystem Stoichiometry: Redox-Dependent and Sodium Ion-Dependent Phosphoryl Transfer from Cyanobacterial Histidine Kinase Hik2 to Response Regulators Rre1 and RppA

“…Our finding, in contrast, shows that the kinase activity of full-length Hik2 protein is modulated by Na + ions (Figure 3 ), and not by Cl − ions. The reason for an apparent inconsistency between the results presented here with purified proteins (Figure 3 ) and those reported for whole cells (Kotajima et al, 2013 ) may be that additional, unspecified interactions occur in vivo .…”

“…We found that Cl − ions do not affect the autokinase activity of Hik2 (Figure 3A , lane 5). Interestingly, a chimeric sensor kinase, made up of the sensor domain of Hik2 and the kinase domain of Hik7, has been reported to respond to Cl − ions in vivo (Kotajima et al, 2013 ). Our finding, in contrast, shows that the kinase activity of full-length Hik2 protein is modulated by Na + ions (Figure 3 ), and not by Cl − ions.…”

Chlorosis as a Developmental Program in Cyanobacteria: The Proteomic Fundament for Survival and Awakening

“…Among these fast-responding proteins are three histidine kinases from two-component systems: Hik8 (Slr0750), Hik11 (Slr1414), and Hik33 (Sll0698). The gene hik11 is essential, but its product has not yet been characterized (56). Hik8 interacts with the circadian rhythm protein KaiC, thereby regulating transcription of genes encoding enzymes involved in carbohydrate metabolism in response to the day-night cycle.…”

Nitrogen chlorosis in unicellular cyanobacteria – a developmental program for surviving nitrogen deprivation

“…Its orthologue in S. elongatus links circadian clock output to carbohydrate metabolism (Osanai et al, 2015). Of the 47 histidine kinases in Synechocystis, Hik 11 is one of three essential ones (Kotajima et al, 2014). Hik33, the Synechocystis homologue of NblS, mediates responses to diverse abiotic stresses, among them cold, salt and high light stress (Ge et al, 2017).…”