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Method for Efficient Refolding and Purification of Chemoreceptor Ligand Binding Domain
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Tuning a bacterial chemoreceptor with protein-membrane interactions.

Roger R Draheim1, Arjan F Bormans, Run-Zhi Lai

  • 1Department of Biology, 3258 TAMU, Texas A&M University, College Station, Texas 77843, USA.

Biochemistry
|December 6, 2006
PubMed
Summary

Residue repositioning in Escherichia coli chemoreceptors fine-tunes signaling. Specific aromatic residues in transmembrane helix 2 modulate receptor activity, with larger changes overwhelming cellular adaptation mechanisms.

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • Chemoreceptors in Escherichia coli are transmembrane proteins crucial for sensing environmental stimuli and controlling flagellar motility.
  • These receptors possess periplasmic domains for chemoeffector binding and cytoplasmic domains for signal transduction and adaptation.
  • The second transmembrane helix (TM2) links these domains and contains aromatic residues interacting with the membrane interface.

Purpose of the Study:

  • To investigate the role of specific aromatic residues (Trp-209 and Tyr-210) in the TM2 helix of the aspartate chemoreceptor (Tar).
  • To determine how repositioning these residues affects the receptor's baseline signaling state and its response to stimuli.
  • To understand the limits of the cellular adaptation system in compensating for altered receptor signaling.

Main Methods:

  • Site-directed mutagenesis was used to reposition the Trp-209/Tyr-210 residue pair in single-residue increments.
  • The baseline signaling activity of the modified receptors was assessed.
  • The ability of adaptive methylation/demethylation to compensate for signaling changes was evaluated.

Main Results:

  • Small, incremental shifts of the Trp-209/Tyr-210 pair (WY-2 to WY+1) predictably modulated the receptor's baseline signaling.
  • These modulations could be compensated by the cell's adaptive methylation system.
  • Larger displacements (WY-3, WY+2, WY+3) resulted in significant receptor bias towards either inhibition or stimulation, exceeding the compensation capacity of the adaptation system.

Conclusions:

  • The precise positioning of aromatic residues within the TM2 helix is critical for maintaining normal chemoreceptor signaling.
  • The cellular adaptation system has limits in compensating for drastic alterations in receptor signaling.
  • Analogous aromatic residues in other chemoreceptors and sensor kinases likely play similar regulatory roles.