体外KaiC磷酸化的昼夜节律振荡机制
Mechanism of robust circadian oscillation of KaiC phosphorylation in vitro
摘要：
通过将三种蓝藻蛋白KaiA、KaiB和KaiC的混合物与ATP在体外孵育，Kondo和他的同事重建了KaiC磷酸化水平的强大昼夜节律（Science，308; 414-415（2005））。这一发现表明，蛋白质相互作用和相关的ATP水解足以产生昼夜节律。已经提出了几种理论模型来解释这种“仅蛋白质”系统中产生的节律，但尚不清楚区分不同可能机制的明确标准。在本文中，我们讨论了一个模型的基础上的两个基本假设：一个KaiC六聚体的变构转换的假设和KaiC六聚体之间的单体交换的假设。该模型显示了KaiC磷酸化水平的稳定节律振荡，这对Kai蛋白浓度的变化是稳健的。我们表明，这种鲁棒性提供了一个线索，以区分不同的可能机制。我们还讨论了振动对系统大小变化的鲁棒性。细胞或亚细胞大小的系统的行为应该阐明蛋白质相互作用在体内昼夜节律振荡中的作用。
英文摘要：
By incubating the mixture of three cyanobacterial proteins, KaiA, KaiB, and KaiC, with ATP in vitro, Kondo and his colleagues reconstituted the robust circadian rhythm of the phosphorylation level of KaiC (Science, 308; 414-415 (2005)). This finding indicates that protein-protein interactions and the associated hydrolysis of ATP suffice to generate the circadian rhythm. Several theoretical models have been proposed to explain the rhythm generated in this "protein-only" system, but the clear criterion to discern different possible mechanisms was not known. In this paper, we discuss a model based on the two basic assumptions: The assumption of the allosteric transition of a KaiC hexamer and the assumption of the monomer exchange between KaiC hexamers. The model shows a stable rhythmic oscillation of the phosphorylation level of KaiC, which is robust against changes in concentration of Kai proteins. We show that this robustness gives a clue to distinguish different possible mechanisms. We also discuss the robustness of oscillation against the change in the system size. Behaviors of the system with the cellular or subcellular size should shed light on the role of the protein-protein interactions in in vivo circadian oscillation.
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