Tetrameric architecture of the circadian clock protein KaiB - A novel interface for intermolecular interactions and its impact on the circadian rhythm
Tetrameric architecture of the circadian clock protein KaiB - A novel interface for intermolecular interactions and its impact on the circadian rhythm
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DOI：
10.1074/jbc.m411284200
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发表时间：
2005-05-13
影响因子：
4.8
通讯作者：
Getzoff, ED
中科院分区：
文献类型：
--
作者：
Hitomi, K;Oyama, T;Getzoff, ED
蓝细菌是最简单的生物体之一，表现出每日的节奏。它们的昼夜节律由各种蛋白质（包括KaiA、KaiB、KaiC和SasA）的定位、相互作用和积累组成。我们已经确定了1.9埃分辨率的结晶结构的蓝藻KaiB时钟蛋白集胞藻。PCC 6803。这种同源四聚体结构揭示了蛋白质-蛋白质相互作用的新型KaiB界面;一个亚基的突出疏水螺旋-转角-螺旋基序适合于相邻亚基的两个β-链之间的凹槽。一个蓝藻突变体，其中的天冬氨酸-赖氨酸盐桥介导这四聚体形成的相互作用被破坏的突变的天冬氨酸甘氨酸，表现出严重受损的节律性（一个短的自由运行期，类似于19小时）。KaiB四聚体形成一个开放的正方形，周边有带正电的残基。KaiB位于富含磷脂的膜上，并易位到胞质溶胶中与其他Kai组分KaiA和KaiC相互作用。KaiB拮抗KaiA对KaiC的作用，并与SasA激酶共享序列同源结构域。基于我们的结构，我们讨论KaiB在生物钟中的功能作用。
Cyanobacteria are among the simplest organisms that show daily rhythmicity. Their circadian rhythms consist of the localization, interaction, and accumulation of various proteins, including KaiA, KaiB, KaiC, and SasA. We have determined the 1.9-angstrom resolution crystallographic structure of the cyanobacterial KaiB clock protein from Synechocystis sp. PCC6803. This homotetrameric structure reveals a novel KaiB interface for protein-protein interaction; the protruding hydrophobic helix-turn-helix motif of one subunit fits into a groove between two beta-strands of the adjacent subunit. A cyanobacterial mutant, in which the Asp-Lys salt bridge mediating this tetramer-forming interaction is disrupted by mutation of Asp to Gly, exhibits severely impaired rhythmicity (a short free-running period; similar to 19 h). The KaiB tetramer forms an open square, with positively charged residues around the perimeter. KaiB is localized on the phospholipid-rich membrane and translocates to the cytosol to interact with the other Kai components, KaiA and KaiC. KaiB antagonizes the action of KaiA on KaiC, and shares a sequence-homologous domain with the SasA kinase. Based on our structure, we discuss functional roles for KaiB in the circadian clock.