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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Identification of key phosphorylation sites in the circadian clock protein KaiC by crystallographic and mutagenetic analyses
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Identification of key phosphorylation sites in the circadian clock protein KaiC by crystallographic and mutagenetic analyses

机译：通过晶体学和诱变分析鉴定昼夜节律蛋白KaiC中的关键磷酸化位点

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摘要

in cyanobacteria, KaiC is an essential hexameric clock protein that forms the core of a circadian protein complex. KaiC can be phosphorylated, and the ratio of phospho-KaiC to non-phospho-KaiC is correlated with circadian period. Structural analyses of KaiC crystals identify three potential phosphorylation sites within a 10-Angstrom radius of the ATP binding regions that are at the T432, S431, and T426 residues in the KaiCII domains. When these residues are mutated by alanine substitution singly or in combination, KaiC phosphorylation is altered, and circadian rhythmicity is abolished. These alanine substitutions do not prevent KaiC from hexamerizing. Intriguingly, the ability of KaiC overexpression to repress its own promoter is also not prevented by alanine substitutions at these sites, implying that the capability of KaiC to repress its promoter is not sufficient to allow the clockwork to oscillate. The KaiC structure and the mutational analysis suggest that S431 and T426 may share a phosphate that can shuttle between these two residues. Because the phosphorylation status of KaiC oscillates over the daily cycle, and KaiC phosphorylation is essential for clock function as shown here, daily modulations of KaiC activity by phosphorylation at T432 and S431/T426 seem to be key components of the circadian clockwork in cyanobacteria.
机译：在蓝细菌中，KaiC是必不可少的六聚体时钟蛋白，可形成昼夜节律蛋白复合物的核心。 KaiC可以被磷酸化，并且磷酸-KaiC与非磷酸-KaiC的比例与昼夜节律有关。 KaiC晶体的结构分析确定了ATP结合区10埃半径内三个可能的磷酸化位点，它们位于KaiCII域的T432，S431和T426残基处。当这些残基单独或组合地通过丙氨酸取代而突变时，KaiC磷酸化被改变，昼夜节律被消除。这些丙氨酸取代不会阻止KaiC进行六聚化。有趣的是，在这些位点通过丙氨酸取代也不能阻止KaiC过度表达抑制其自身启动子的能力，这意味着KaiC抑制其启动子的能力不足以使发条振荡。 KaiC结构和突变分析表明，S431和T426可能共享一个可以在这两个残基之间穿梭的磷酸盐。因为KaiC的磷酸化状态会在每天的周期中振荡，并且KaiC磷酸化对于时钟功能至关重要，如此处所示，所以通过T432和S431 / T426的磷酸化来日常调节KaiC活性似乎是蓝细菌昼夜节律的关键组成部分。

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