Segmental Helical Motions and Dynamical Asymmetry Modulate Histidine Kinase Autophosphorylation

Histidine kinases (HKs) are dimeric receptors that participate in most adaptive responses to environmental changes in prokaryotes. Although it is well established that stimulus perception triggers autophosphorylation in many HKs, little is known on how the input signal propagates through the HAMP domain to control the transient interaction between the histidine-containing and ATP-binding domains during the catalytic reaction. Here we report crystal structures of the full cytoplasmic region of CpxA, a prototypical HK involved in Escherichia coli response to envelope stress. The structural ensemble, which includes the Michaelis complex, unveils HK activation as a highly dynamic process, in which HAMP modulates the segmental mobility of the central HK α-helices to promote a strong conformational and dynamical asymmetry that characterizes the kinase-active state. A mechanical model based on our structural and biochemical data provides insights into HAMP-mediated signal transduction, the autophosphorylation reaction mechanism, and the symmetry-dependent control of HK kinase/phosphatase functional states.组氨酸激酶（Histidine kinases, HKs）是一类二聚化受体，参与原核生物绝大多数针对环境变化的适应性应答过程。尽管学界已明确，刺激感知可触发多数组氨酸激酶的自磷酸化反应，但目前对于催化过程中，输入信号如何通过HAMP结构域（HAMP domain）传播，以调控含组氨酸结构域与ATP结合结构域之间的瞬时相互作用，仍缺乏深入认知。本研究解析了CpxA完整胞质区的晶体结构，CpxA是参与大肠杆菌（Escherichia coli）包膜应激应答的典型组氨酸激酶。该结构集合包含米氏复合物（Michaelis complex），其揭示组氨酸激酶的激活是一个高度动态的过程：在此过程中，HAMP结构域可调控组氨酸激酶中央α螺旋的节段运动性，进而促成强烈的构象与动态不对称性，这正是激酶激活状态的典型特征。基于本研究的结构与生化数据构建的力学模型，可为HAMP介导的信号转导、自磷酸化反应机制，以及组氨酸激酶激酶/磷酸酶功能状态的对称性调控提供新的理论视角。