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The inner membrane histidine kinase EnvZ senses osmolality via helix‐coil transitions in the cytoplasm
Author(s) -
Wang Loo Chien,
Morgan Leslie K,
Godakumbura Pahan,
Kenney Linda J,
Anand Ganesh S
Publication year - 2012
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/emboj.2012.99
Subject(s) - biology , cytoplasm , histidine , helix (gastropod) , histidine kinase , biophysics , microbiology and biotechnology , membrane protein , phosphorylation , biochemistry , membrane , amino acid , zoology , gastropoda
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.