Structure of the Native Chemotaxis Core Signalling Unit from E-gene lysed E. coli cells
Motile bacteria detect ambient chemical gradients and control their locomotion via conserved chemotaxis signaling networks, enabling cells to locate nutrients, potential hosts and other important biological niches. The sensory apparatus of the chemotaxis pathway is an array of core-signaling units (CSU) composed of transmembrane chemoreceptors, the histidine kinase CheA and an adaptor protein CheW. Although chemotaxis pathways represent the best understood signaling systems, a detailed mechanistic understanding of signal transduction has been hindered by the lack of a complete structural picture of the CSU and extended array. In this study, we present the structure of the complete CSU from phage E-gene lysed E. coli cells, determined using cryo-electron tomography and sub-tomogram averaging to 12 [A] resolution. Using AlphaFold2, we further predict the atomic structures of the CSUs constituent proteins as well as key protein-protein interfaces, enabling the assembly an all-atom CSU model, which we conformationally refine using our cryoET map. Molecular dynamics simulations of the resulting model provide new insight into the periplasmic organization of the complex, including novel interactions between neighboring receptor ligand binding domains. Our results further elucidate previously unresolved interactions between individual CheA domains, including an anti-parallel P1 dimer and non-productive binding mode between P1 and P4, enhancing our understanding of the structural mechanisms underlying CheA signaling and regulation.