Flexibility of the C-terminal, or CII, ring of KaiC governs the rhythm of the circadian clock of cyanobacteria
Flexibility of the C-terminal, or CII, ring of KaiC governs the rhythm of the circadian clock of cyanobacteria
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DOI：
10.1073/pnas.1104221108
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发表时间：
2011-08-30
影响因子：
11.1
通讯作者：
LiWang, Andy
中科院分区：
文献类型：
--
作者：
Chang, Yong-Gang;Kuo, Nai-Wei;LiWang, Andy
在蓝藻昼夜节律振荡器中，KaiA和KaiB以大约24小时的周期交替刺激KaiC的自磷酸化和自去磷酸化。 KaiA 通过选择性捕获 KaiC 暴露位置的 A 环来激活自身磷酸化。 A 环和磷酸化位点（残基 S431 和 T432）位于 KaiC 的 CII 环中。我们发现 CII 环的灵活性控制着 KaiC 自磷酸化和自去磷酸化的节律，是动力学驱动的蛋白质变构的一个例子。 KaiA 诱导的自磷酸化需要 CII 环的灵活性。相比之下，KaiC-KaiB 结合需要刚性，这会诱导 KaiB 发生构象变化，使其能够通过与 KaiA 的接头结合来隔离 KaiA。 CII 环周围的 S431 残基的自磷酸化可稳定 CII 环，使其变得刚性。相反，T432 残基的自磷酸化在一定程度上抵消了 phos-pho-S431 诱导的刚性。在 KaiA 和 KaiB 存在的情况下，KaiC 的 CII 环的动态执行以下昼夜节律：CIIflexibleST -> CIIflexibleSpT -> CIIrigidpSpT -> CIIvery-rigidpST -> CIIflexibleST。显然，这些动态控制着磷酸化模式，ST -> SpT -> pSpT -> pST -> ST。当 CII 环刚性时，可以观察到 CII-CI 环上环堆积，这表明 CI 环的 ATP 酶活性受到节律控制的机制。 SasA 是一种生物钟输出蛋白，与 CI 环结合。因此，有节奏的环堆叠也可以控制时钟输出路径。
In the cyanobacterial circadian oscillator, KaiA and KaiB alternately stimulate autophosphorylation and autodephosphorylation of KaiC with a periodicity of approximately 24 h. KaiA activates autophosphorylation by selectively capturing the A loops of KaiC in their exposed positions. The A loops and sites of phosphorylation, residues S431 and T432, are located in the CII ring of KaiC. We find that the flexibility of the CII ring governs the rhythm of KaiC autophosphorylation and autodephosphorylation and is an example of dynamics-driven protein allostery. KaiA-induced autophosphorylation requires flexibility of the CII ring. In contrast, rigidity is required for KaiC-KaiB binding, which induces a conformational change in KaiB that enables it to sequester KaiA by binding to KaiA's linker. Autophosphorylation of the S431 residues around the CII ring stabilizes the CII ring, making it rigid. In contrast, autophosphorylation of the T432 residues offsets phos-pho-S431-induced rigidity to some extent. In the presence of KaiA and KaiB, the dynamic states of the CII ring of KaiC executes the following circadian rhythm: CIIflexibleST -> CIIflexibleSpT -> CIIrigidpSpT -> CIIvery-rigidpST -> CIIflexibleST. Apparently, these dynamic states govern the pattern of phosphorylation, ST -> SpT -> pSpT -> pST -> ST. CII-CI ring-on-ring stacking is observed when the CII ring is rigid, suggesting a mechanism through which the ATPase activity of the CI ring is rhythmically controlled. SasA, a circadian clock-output protein, binds to the CI ring. Thus, rhythmic ring stacking may also control clock-output pathways.