Signal Transduction and Kinase Control in Nanodisc-ReconstitutedE. coliAerotaxis Receptor

Abstract Sensing of external chemical gradients is coupled to flagellar motility in bacteria through use, in part, of dimeric transmembrane Methyl-Accepting Chemotaxis Proteins, or MCPs. In E. coli , periplasmic MCP sensory domains convey conformational signals across the inner membrane, through a cytoplasmic HAMP domain and to a coiled-coil Kinase Control Domain (KCD). The MCP KCD modulates the autophosphorylation level of a dedicated histidine kinase CheA; subsequent phosphotransfer to a secondary messenger CheY transmits the chemotactic signal directly to the flagellar motor and affects rotation. The MCP Kinase Control Domain affects CheA autophosphorylation through complex structural and dynamical changes and also undergoes reversible adaptive methylation at conserved residues mediated by methyltransferase CheR and methylesterase CheB that aids in tracking chemical gradients. Here, we used Double Electron-Electron Resonance Pulse Dipolar ESR experiments to probe dynamical and structural differences in the Kinase Control Domain of Aer, the E. coli aerotaxis receptor, between its kinase-on and kinase-of signaling states. The evidence presented here suggests that the Aer kinase-off signaling state is characterized by ejection of the C-terminal region of the C-terminal Kinase Control Domain Helix, tied with complex dynamical changes along the KCD axis. Furthermore, Mass Spectrometry analysis of Aer grown in CheR and CheB knockout E. coli strains demonstrates that Aer undergoes methylation, contrary to previous work, and suggests different patterns of methylation for the Aer N- and C-terminal Kinase Control Domain helices.