Histidine kinase receptors respond to diverse signals and mediate signal transduction across the plasma membrane in all prokaryotes and certain eukaryotes. Each receptor is part of a two-component system that regulates a particular cellular process. Organisms that use trimethylamine-N-oxide (TMAO) as a terminal electron acceptor typically control their anaerobic respiration through the TMAO reductase (Tor) pathway, which the TorS histidine kinase activates when sensing TMAO in the environment. We have determined crystal structures for the periplasmic sensor domains of TorS receptors from Escherichia coli and Vibrio parahaemolyticus, as well as crystal structures of the TorT-TorSS complex from V. parahaemolyticus in the presence and absence of TMAO. TorS sensor domains have a novel fold consisting of a membrane-proximal right-handed four-helical bundle and a membrane-distal left-handed four-helical bundle whereas TorT is structurally a periplasmic binding protein. They form a 2:2 heterotetramer arranged so that the two protomers of TorSS associate along their long axis with the two protomers of TorT associating with the membrane distal domains of both TorSS protomers but make no contact with each other. Structural differences between the different bound states are subtle but the end result resembles a mix of the perpendicular rotation and the piston type displacement models. Through a series of genetic and biochemical experiments we determined the residues that bind TMAO, the importance of a flexible loop near the binding cleft of TorT, the effect of TMAO on the stability of the TorT-TorS complex, and generated a chimera composed of the NarX-TorS chimera that is sensitive to nitrate.
|School Location:||United States -- New York|
|Source:||DAI-B 71/02, Dissertation Abstracts International|
|Keywords:||Histidine kinase, Trimethylamine oxide|
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