Slow and temperature-compensated autonomous disassembly of KaiB-KaiC complex

KaiC is the central pacemaker of the circadian clock system in cyanobacteria and forms the core in the heteromultimeric complexes, such as KaiB-KaiC and KaiA-KaiB-KaiC. Although the formation process and structure of the binary and ternary complexes have been studied extensively, their disassembly dynamics have. remained elusive. In this study, we constructed an experimental system to directly measure the autonomous disaembly of the KaiB-KaiC complex under the condition where the dissociated KaiB cannot reassociate with KaiC. At 30 degrees C, the dephosphorylated KaiB-KaiC complex disassembled with an apparent rate of 2.1 +/- 0.3 d(-1), was approximately twice the circadian frequency. Our present analysis using a series of KaiC mutants revealed that the apparent disassembly rate correlates with the frequency of the KaiC phosphorylation cycle in the presence of KniA and KaiB and is robustly temperature-compensated with a Q(10) value of 1.05 +/- 0.20. The autonomous cancellation of the interactions stabilizing the KniB-KaiC interface is one of the important phenomena that provide a link between the molecular-scale and system-scale properties.