title: The inner membrane histidine kinase EnvZ senses osmolality via helix-coil transitions in the cytoplasm.
abstract: Two-component systems mediate bacterial signal transduction, employing a membrane sensor kinase and a cytoplasmic response regulator (RR). Environmental sensing is typically coupled to gene regulation. Understanding how input stimuli activate kinase autophosphorylation remains obscure. The EnvZ/OmpR system regulates expression of outer membrane proteins in response to osmotic stress. To identify EnvZ conformational changes associated with osmosensing, we used HDXMS to probe the effects of osmolytes (NaCl, sucrose) on the cytoplasmic domain of EnvZ (EnvZ(c)). Increasing osmolality decreased deuterium exchange localized to the four-helix bundle containing the autophosphorylation site (His(243)). EnvZ(c) exists as an ensemble of multiple conformations and osmolytes favoured increased helicity. High osmolality increased autophosphorylation of His(243), suggesting that these two events are linked. In-vivo analysis showed that the cytoplasmic domain of EnvZ was sufficient for osmosensing, transmembrane domains were not required. Our results challenge existing claims of robustness in EnvZ/OmpR and support a model where osmolytes promote intrahelical H-bonding enhancing helix stabilization, increasing autophosphorylation and downstream signalling. The model provides a conserved mechanism for signalling proteins that respond to diverse physical and mechanical stimuli.
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore, Singapore.
authors.forename: Loo Chien
authors.initials: LC
authors.lastname: Wang
authors.forename: Leslie K
authors.initials: LK
authors.lastname: Morgan
authors.forename: Pahan
authors.initials: P
authors.lastname: Godakumbura
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Kenney
authors.forename: Ganesh S
authors.initials: GS
authors.lastname: Anand
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D003593:Cytoplasm / Q000737:chemistry / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D006639:Histidine / Q000378:metabolism; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009994:Osmolar Concentration; D017433:Protein Structure, Secondary / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D012965:Sodium Chloride / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D012965:Sodium Chloride; D006639:Histidine; D013395:Sucrose; C057843:envZ protein, E coli