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Related Experiment Video

Updated: Sep 8, 2025

Imaging G-protein Coupled Receptor GPCR-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum
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A chemoreceptor conformational equilibrium controlled by signaling inputs.

Mikaila C Hoffman1, Mingshan Li2, Gerald L Hazelbauer2

  • 1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.

Proceedings of the National Academy of Sciences of the United States of America
|July 9, 2025
PubMed
Summary
This summary is machine-generated.

Bacteria use chemoreceptors for directed movement. This study reveals ligand binding and modification alter receptor geometry, not just switching states, impacting bacterial chemotaxis signaling.

Keywords:
bacterial chemotaxissingle-molecule FRETtransmembrane receptors

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Area of Science:

  • Microbiology
  • Biochemistry
  • Structural Biology

Background:

  • Bacteria navigate chemical gradients via chemotaxis, a process mediated by transmembrane chemoreceptors.
  • Chemoreceptors signal across the cell membrane, controlling downstream pathways and undergoing modifications for adaptation.
  • Current models propose chemoreceptors switch between two distinct signaling states (kinase-off and kinase-on) based on ligand binding and modification.

Purpose of the Study:

  • To investigate the conformational equilibrium of the *Escherichia coli* aspartate chemoreceptor Tar.
  • To determine how ligand occupancy and adaptational modification influence this equilibrium.
  • To clarify the structural basis of transmembrane signaling in bacterial chemotaxis.

Main Methods:

  • Single-molecule Förster resonance energy transfer (smFRET) was employed to monitor helical separations.
  • Measurements focused on the cytoplasmic four-helix coiled coil bundle of the Tar receptor.
  • Conformational changes were analyzed under varying conditions of ligand occupancy and adaptational modification.

Main Results:

  • Two distinct helical separations were observed in each helical pair under all conditions, differing in relative occupancy.
  • Ligand occupancy shifted the bundle from symmetrical to rhomboid packing.
  • Adaptational modification influenced which helical pair occupied the central position within the rhomboid packing.

Conclusions:

  • Chemoreceptor signaling involves dynamic shifts in conformational equilibria rather than a simple two-state switch.
  • Ligand binding alters the collective geometry of the four-helix bundle, impacting signaling.
  • These findings offer new insights into transmembrane receptor function and may apply to other receptor systems.