In Situ Conformational Changes of the Escherichia coli Serine Chemoreceptor in Different Signaling States
In Situ Conformational Changes of the Escherichia coli Serine Chemoreceptor in Different Signaling States
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DOI：
10.1128/mbio.00973-19
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发表时间：
2019-07
期刊：
影响因子：
6.4
通讯作者：
Wen Yang;C. K. Cassidy;P. Ames;C. Diebolder;K. Schulten;Z. Luthey-Schulten;J. S. Parkinson;A. Briegel
中科院分区：
文献类型：
--
作者：
Wen Yang;C. K. Cassidy;P. Ames;C. Diebolder;K. Schulten;Z. Luthey-Schulten;J. S. Parkinson;A. Briegel
在大肠杆菌中，膜结合的化学感受器、组氨酸激酶CheA和偶联蛋白CheW形成高度有序的化学感觉阵列。在核心信号复合物中，二聚体的化学受体三聚体在配体结合和感觉适应的诱导下发生构象变化，从而调节激酶的激活。在这里，我们通过低温电子断层扫描表征了大肠杆菌丝氨酸受体在其天然阵列环境中的激酶- on和激酶- off构象。我们发现一个受体三聚体的成员之间存在明显的结构差异，它们在信号单元中与不同的伙伴接触，并且在ON和OFF信号复合物之间存在结构差异。我们的研究结果为化学受体阵列的信号传导机制提供了新的见解，并表明受体分子中先前假设的柔性区域和甘氨酸铰链具有重要的功能作用。Tsr是大肠杆菌中的丝氨酸化学受体，它将信号从质周配体结合位点转导到细胞质尖端，在那里它控制CheA激酶的活性。为了发挥作用，Tsr形成同型二聚体三聚体（TODs），其在体内与CheA激酶和CheW偶联蛋白结合。这些蛋白质一起组装成扩展的六边形阵列。在这里，我们使用低温电子断层扫描和分子动力学模拟来研究Tsr在近天然阵列的背景下，表征其在个体二聚体和三聚体水平上与信号相关的构象变化。特别是，我们发现三聚体中的单个Tsr二聚体表现出不对称的灵活性，这是信号状态的功能，突出了它们在受体尖端的不同蛋白质相互作用的影响。我们进一步揭示了Tsr三聚体的二聚体紧密性在不同的信号状态下发生变化，在甘氨酸铰链处从激酶关闭状态的紧凑构象过渡到激酶打开状态的扩展构象。因此，我们的研究结果支持了甘氨酸铰链的关键作用：允许受体实现不同信号状态所需的灵活性，同时保持膜和扩展阵列结构施加的结构约束。在大肠杆菌中，膜结合的化学感受器、组氨酸激酶CheA和偶联蛋白CheW形成高度有序的化学感觉阵列。在核心信号复合物中，二聚体的化学受体三聚体在配体结合和感觉适应的诱导下发生构象变化，从而调节激酶的激活。在这里，我们通过低温电子断层扫描表征了大肠杆菌丝氨酸受体在其天然阵列环境中的激酶- on和激酶- off构象。我们发现一个受体三聚体的成员之间存在明显的结构差异，它们在信号单元中与不同的伙伴接触，并且在ON和OFF信号复合物之间存在结构差异。我们的研究结果为化学受体阵列的信号传导机制提供了新的见解，并表明受体分子中先前假设的柔性区域和甘氨酸铰链具有重要的功能作用。
In Escherichia coli, membrane-bound chemoreceptors, the histidine kinase CheA, and coupling protein CheW form highly ordered chemosensory arrays. In core signaling complexes, chemoreceptor trimers of dimers undergo conformational changes, induced by ligand binding and sensory adaptation, which regulate kinase activation. Here, we characterize by cryo-electron tomography the kinase-ON and kinase-OFF conformations of the E. coli serine receptor in its native array context. We found distinctive structural differences between the members of a receptor trimer, which contact different partners in the signaling unit, and structural differences between the ON and OFF signaling complexes. Our results provide new insights into the signaling mechanism of chemoreceptor arrays and suggest an important functional role for a previously postulated flexible region and glycine hinge in the receptor molecule. ABSTRACT Tsr, the serine chemoreceptor in Escherichia coli, transduces signals from a periplasmic ligand-binding site to its cytoplasmic tip, where it controls the activity of the CheA kinase. To function, Tsr forms trimers of homodimers (TODs), which associate in vivo with the CheA kinase and CheW coupling protein. Together, these proteins assemble into extended hexagonal arrays. Here, we use cryo-electron tomography and molecular dynamics simulation to study Tsr in the context of a near-native array, characterizing its signaling-related conformational changes at both the individual dimer and the trimer level. In particular, we show that individual Tsr dimers within a trimer exhibit asymmetric flexibilities that are a function of the signaling state, highlighting the effect of their different protein interactions at the receptor tips. We further reveal that the dimer compactness of the Tsr trimer changes between signaling states, transitioning at the glycine hinge from a compact conformation in the kinase-OFF state to an expanded conformation in the kinase-ON state. Hence, our results support a crucial role for the glycine hinge: to allow the receptor flexibility necessary to achieve different signaling states while also maintaining structural constraints imposed by the membrane and extended array architecture. IMPORTANCE In Escherichia coli, membrane-bound chemoreceptors, the histidine kinase CheA, and coupling protein CheW form highly ordered chemosensory arrays. In core signaling complexes, chemoreceptor trimers of dimers undergo conformational changes, induced by ligand binding and sensory adaptation, which regulate kinase activation. Here, we characterize by cryo-electron tomography the kinase-ON and kinase-OFF conformations of the E. coli serine receptor in its native array context. We found distinctive structural differences between the members of a receptor trimer, which contact different partners in the signaling unit, and structural differences between the ON and OFF signaling complexes. Our results provide new insights into the signaling mechanism of chemoreceptor arrays and suggest an important functional role for a previously postulated flexible region and glycine hinge in the receptor molecule.