Kageyama Hakuto, Nishiwaki Taeko, Nakajima Masato, Iwasaki Hideo, Oyama Tokitaka, Kondo Takao
Division of Biological Science, Graduate School of Science, Nagoya University and CREST & SORST, Japan Science and Technology Corporation, Furo-cho 1, Chikusa, Nagoya 464-8602, Japan.
Mol Cell. 2006 Jul 21;23(2):161-71. doi: 10.1016/j.molcel.2006.05.039.
KaiA, KaiB, and KaiC are essential proteins of the circadian clock in the cyanobacterium Synechococcus elongatus PCC 7942. The phosphorylation cycle of KaiC that occurs in vitro after mixing the three proteins and ATP is thought to be the master oscillation governing the circadian system. We analyzed the temporal profile of complexes formed between the three Kai proteins. In the phosphorylation phase, KaiA actively and repeatedly associated with KaiC to promote KaiC phosphorylation. High levels of phosphorylation of KaiC induced the association of the KaiC hexamer with KaiB and inactivate KaiA to begin the dephosphorylation phase, which is closely linked to shuffling of the monomeric KaiC subunits among the hexamer. By reducing KaiC phosphorylation, KaiB dissociated from KaiC, reactivating KaiA. We also confirmed that a similar model can be applied in cyanobacterial cells. The molecular model proposed here provides mechanisms for circadian timing systems.
KaiA、KaiB和KaiC是聚球藻属蓝细菌（Synechococcus elongatus PCC 7942）生物钟的必需蛋白。在将这三种蛋白质与ATP混合后体外发生的KaiC磷酸化循环被认为是控制生物钟系统的主要振荡。我们分析了这三种Kai蛋白之间形成的复合物的时间分布。在磷酸化阶段，KaiA与KaiC积极且反复地结合，以促进KaiC磷酸化。高水平的KaiC磷酸化诱导KaiC六聚体与KaiB结合，并使KaiA失活，从而开始去磷酸化阶段，这与六聚体中单体KaiC亚基的重排密切相关。通过降低KaiC磷酸化，KaiB从KaiC上解离，使KaiA重新激活。我们还证实了类似的模型可应用于蓝细菌细胞。这里提出的分子模型为生物钟计时系统提供了机制。
