Dynamic Clustering of the Bacterial Sensory Kinase BaeS

Several bacterial sensory-kinase receptors form clusters on the cell membrane. However, the dynamics of sensory-kinase clustering are largely unclear. Using measurements of fluorescence anisotropy and time-lapse imaging of Escherichia coli cells, we demonstrate that copper ions trigger self-association of BaeS receptors and lead to rapid formation of clusters, which can be reversibly dispersed by a metal chelator. Copper ions did not trigger self-association of other fluorescently tagged sensory kinases, and other divalent metal ions could not elicit self-association of BaeS. The histidine residues in the BaeS periplasmic domain are essential for copper binding in vitro and are important for the copper-induced BaeS responses in vivo. BaeS clustering was triggered also under conditions that directly triggered BaeS-dependent transcriptional responses. Thus, clustering of sensory kinase receptors can be dynamic and context dependent and can be triggered by specific environmental cues.多种细菌的传感激酶受体可在细胞膜上形成簇集结构，但目前学界对传感激酶簇集的动态变化机制仍知之甚少。本研究通过对大肠杆菌（Escherichia coli）细胞开展荧光各向异性（fluorescence anisotropy）检测与延时成像（time-lapse imaging）分析，证实铜离子可诱导BaeS受体发生自缔合，进而快速形成簇集结构，且该簇集可被金属螯合剂可逆解离。铜离子无法诱导其他荧光标记传感激酶发生自缔合，而其他二价金属离子也无法引发BaeS的自缔合反应。BaeS周质结构域内的组氨酸残基是体外（in vitro）结合铜离子的必需位点，同时对体内（in vivo）铜离子诱导的BaeS响应至关重要。在可直接触发BaeS依赖型转录响应的实验条件下，同样可观察到BaeS的簇集现象。综上，传感激酶受体的簇集是动态且依赖于环境背景的过程，可由特定环境信号触发。