Structure and Dynamics of the E. coli Chemotaxis Core Signalling Complex

Abstract

Chemotactic bacteria, including numerous human and plant pathogens, navigate their habitats using large, multi-component protein arrays. Through the binding of environmental chemical ligands, these sophisticated arrays transduce highly-cooperative sensory signals over large distances, giving rise to an intracellular phosphorylation cascade that ultimately affects cell swimming pattern. The basic building block of the array, known as the core-signalling unit (CSU), comprises six transmembrane chemoreceptors, a dimeric histidine kinase, and two coupling proteins, which together span over 30 nm and have a molecular weight of more than 900 kDa. Despite considerable effort over the years, the large size and dynamic nature of the CSU have thwarted the determination of a high-resolution structure, rendering detailed molecular descriptions of array function difficult to resolve. Here, we present recent integrative modelling work, combining cryo-electron tomography structures of the E. coli CSU derived separately from reconstituted monolayer arrays and a newly-characterized minicell strain, to produce the first atomistic model of a complete, transmembrane CSU. This model, combined with all-atom molecular dynamics simulation, allows for a detailed investigation of kinase conformational dynamics, identifying multiple conformations of the critical catalytic and dimerization domains and highlighting residue-level features of their differential stabilization. In addition, Martini-based coarse-grained simulations provide insights into the previously-unresolved membrane-proximal regions of the CSU, characterizing key protein-lipid interactions as well as inter-receptor dynamics within the bilayer. These results provide a structural and methodological basis for testing and understanding molecular signalling mechanisms broadly within bacterial chemosensing