Cross-scale Analysis of Temperature Compensation in the Cyanobacterial Circadian Clock System

Abstract

Clock proteins maintain constant enzymatic activity regardless of temperature, even though thermal fluctuation is accelerated as temperature increases. We investigated temperature influences on the dynamics of KaiC, a temperature-compensated ATPase in the cyanobacterial circadian clock system, using quasielastic neutron scattering. The frequency of picosecond to sub-nanosecond incoherent local motions in KaiC was accelerated very slightly in a temperature-dependent manner. Our mutation studies revealed that internal motions of KaiC include several contributions of opposing temperature sensitivities. To take advantage of this balancing effect, the motional frequency of local dynamics in KaiC needs to exceed ∼0.3 ps-1. Some of the mutation sites may be in a pathway through which the motional frequency in the C-terminal domain of KaiC is fed back to the active site of ATPase in its N-terminal domain. The temperature-compensating ability at the dynamics level is likely crucial for circadian clock systems, into which the clock proteins are incorporated, to achieve reaction- or even system-level temperature compensation of the oscillation frequency.

Role of the reaction-structure coupling in temperature compensation of the KaiABC circadian rhythm

“…A possible test of the thermal weakening of the CI-CII structural coupling is to measure the temperature dependence of the thermal fluctuations of the interface residue with NMR or other spectroscopic methods. The model predicts that the temperature dependence of fluctuations should be anti-correlated with the Q 10 of the period, and such an anti-correlation was suggested from the recent neutron scattering data 68 .…”

“…Assumption of ∆E fs-gs > 0 should affect the binding kinetics of KaiB, and we call this assumption Rule 2. The other assumption corresponds to the temperature insensitivity of the ATPase reactions as observed in experiments 23,68 . We assume the temperature-insensitive ATPase reactions by imposing ∆ 0 ADP (T ) = ∆ 0 ADP (T 0 ) and f hyd (T ) = f hyd (T 0 ), where ∆ 0 ADP (T ) is a constant to determine the lifetime of the ADP bound state (Eq.…”

“…This result suggests that the strategy to keep the specific constraint has been avoided in evolutionary design. Instead, the more general strategy of the temperature-insensitive ATPase reactions might have been evolutionarily realized in KaiC 23,68 as in the TTO regulator, CKIε/δ , in mammals 22 .…”