Molecular Insights into the Signaling Mechanism of the Histidine Kinase CheA within an Intact Bacterial Chemosensory Array

Abstract

The chemotactic response in bacteria relies on the formation of large, highly ordered complexes of sensory proteins, known as chemosensory arrays, which mediate the transduction and regulation of signals that ultimately control cellular motility. Although, a coarse representation of the array's extended organization has recently been sketched out, an outstanding problem concerns the detailed description of the molecular events occurring within the array during signaling. Progress in this area necessitates a high-resolution understanding of the intact chemosensory array structure. Utilizing cryo-electron tomography and 3D subvolume averaging, we have derived density maps of a resolution sufficient for the construction and refinement of an atomic model of the chemosensory array's core structure. Large-scale, all-atom molecular dynamics (MD) simulations of an atomic model of the array unit cell, 1.2 million atoms in size, have revealed the molecular details of the interaction interfaces between the receptor, CheA, and CheW proteins, as well as a distinctive conformational change in CheA kinase domain. Mutagenesis and chemical cross-linking studies have further confirmed the important roles of specific residues at these critical interaction interfaces.