Structure and dynamics of the E. coli chemotaxis core signaling complex by cryo-electron tomography and molecular simulations

C. Keith Cassidy et al. use cryo-electron tomography and subtomogram averaging to examine the structure of the core-signalling units of E. coli chemotaxis arrays at subnanometer resolution. They find multiple distinct conformations of the critical CheA kinase domain, offering new insights into CheA signalling. To enable the processing of chemical gradients, chemotactic bacteria possess large arrays of transmembrane chemoreceptors, the histidine kinase CheA, and the adaptor protein CheW, organized as coupled core-signaling units (CSU). Despite decades of study, important questions surrounding the molecular mechanisms of sensory signal transduction remain unresolved, owing especially to the lack of a high-resolution CSU structure. Here, we use cryo-electron tomography and sub-tomogram averaging to determine a structure of the Escherichia coli CSU at sub-nanometer resolution. Based on our experimental data, we use molecular simulations to construct an atomistic model of the CSU, enabling a detailed characterization of CheA conformational dynamics in its native structural context. We identify multiple, distinct conformations of the critical P4 domain as well as asymmetries in the localization of the P3 bundle, offering several novel insights into the CheA signaling mechanism.