Biology subjects

Terauchi, K.

Publications and source records attributed to Terauchi, K..

3 recordsLinked to original sources

bioRxiv2026

Nucleotide-driven KaiC dynamics coordinate the core properties of the cyanobacterial circadian clock

Circadian clocks generate stable [~]24-h rhythms with a defined period, temperature compensation, and entrainment to external cues that set phase. However, the molecular reactions that generate these features are not fully understood. In cyanobacteria, timekeeping is driven by the hexameric ATPase KaiC, which consists of two homologous domains, CI and CII, and whose enzymatic turnover underlies rhythmic phosphorylation. Here we identify ADP release as the rate-limiting step in the KaiC ATPase cycle and demonstrate that the KaiC ATPase nucleotide cycle integrates core properties of the circadian clock. Across KaiC period mutants, increased ADP occupancy is associated with longer periods. Elevated temperature shifts KaiC toward an ADP-bound state, offsetting the thermal acceleration of ATP hydrolysis. KaiB reinforces this ADP-bound conformation by inhibiting nucleotide exchange, thereby strengthening inhibition of CI ATPase activity of KaiC and tuning oscillation amplitude in a temperature-dependent manner. In contrast, KaiA accelerates ADP-to-ATP exchange within the KaiB-KaiC complex, thereby stimulating CI ATPase activity and promoting KaiB-KaiC dissociation prior to KaiC phosphorylation. Phosphorylation begins only after this transition, indicating that KaiC nucleotide-bound state sets the phase of the phosphorylation cycle. Collectively, these results establish the nucleotide cycle of KaiC ATPase as a unifying mechanism that connects molecular reactions to the defining properties of the cyanobacterial circadian clock.

biochemistry↗

bioRxiv2021

Regulation Mechanisms of the Dual ATPase in KaiC

KaiC is a dual ATPase, with one active site in its N-terminal domain and another in its C-terminal domain, that drives the circadian clock system of cyanobacteria through sophisticated coordination of the two sites. To elucidate the coordination mechanism, we studied the contribution of the dual ATPase activities in the ring-shaped KaiC hexamer and these structural bases for activation and inactivation. At the N-terminal active site, a lytic water molecule is sequestered between the N-terminal domains, and its reactivity to ATP is controlled by the quaternary structure of the N-terminal ring. The C-terminal ATPase activity is regulated mostly by water-incorporating voids between the C-terminal domains, and the size of these voids is sensitive to phosphoryl modification of S431. The N-terminal ATPase activity inversely correlates with the affinity of KaiC for KaiB, a clock protein constitutes the circadian oscillator together with KaiC and KaiA, and the complete dissociation of KaiB from KaiC requires KaiA-assisted activation of the dual ATPase. Delicate interactions between the N-terminal and C-terminal rings make it possible for the components of the dual ATPase to work together, thereby driving the assembly and disassembly cycle of KaiA and KaiB. Significance StatementKaiC, a core clock protein in the cyanobacterial circadian clock system, hydrolyzes ATP at two distinct sites in a slow but ordered manner to measure the circadian time scale. We used biochemical and structural biology techniques to characterize the properties and interplay of dual ATPase active sites. Our results show that the N-terminal and C-terminal ATPases communicate with each other through an interface between the N-terminal and C-terminal domains in KaiC. The dual ATPase sites are regulated rhythmically in a concerted or opposing manner dependent on the phase of the circadian clock system, controlling the affinities of KaiC for other clock proteins, KaiA and KaiB.

biochemistry↗

bioRxiv2019

Synechocystis KaiC3 displays temperature and KaiB dependent ATPase activity and is important for viability in darkness

Cyanobacteria form a heterogeneous bacterial group with diverse lifestyles, acclimation strategies and differences in the presence of circadian clock proteins. In Synechococcus elongatus PCC 7942, a unique posttranslational KaiABC oscillator drives circadian rhythms. ATPase activity of KaiC correlates with the period of the clock and mediates temperature compensation. Synechocystis sp. PCC 6803 expresses additional Kai proteins, of which KaiB3 and KaiC3 proteins were suggested to fine-tune the standard KaiAB1C1 oscillator. In the present study, we therefore characterized the enzymatic activity of KaiC3 as a representative of non-standard KaiC homologs in vitro. KaiC3 displayed ATPase activity, which were lower compared to the Synechococcus elongatus PCC 7942 KaiC protein. ATP hydrolysis was temperature-dependent. Hence, KaiC3 is missing a defining feature of the model cyanobacterial circadian oscillator. Yeast two-hybrid analysis showed that KaiC3 interacts with KaiB3, KaiC1 and KaiB1. Further, KaiB3 and KaiB1 reduced in vitro ATP hydrolysis by KaiC3. Spot assays showed that chemoheterotrophic growth in constant darkness is completely abolished after deletion of{Delta} kaiAB1C1 and reduced in the absence of kaiC3. We therefore suggest a role for adaptation to darkness for KaiC3 as well as a crosstalk between the KaiC1 and KaiC3 based systems.

microbiology↗