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Ligand-Gated Ion Channel Receptor: Gating Mechanism

Ligand-gated ion channels are transmembrane proteins that play a vital role in intercellular communication and functions of the nervous system. They allow the influx of ions across the membrane once the neurotransmitter binds, allowing the subsequent transmission of electrical excitation across the neurons. Other ligand-gated ion channels, like the γ-aminobutyric acid (GABA) receptor, permit anions like chloride into the cells on the binding of the GABA molecule. Their entry into the cell...
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Updated: Jun 5, 2026

Modeling Ligands into Maps Derived from Electron Cryomicroscopy
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Blocking the gate to ligand entry in human hemoglobin.

Ivan Birukou1, Jayashree Soman, John S Olson

  • 1Department of Biochemistry and Cell Biology and the W. M. Keck Center for Computational Biology, Rice University, Houston, Texas 77005, USA.

The Journal of Biological Chemistry
|January 4, 2011
PubMed
Summary

Mutations in human hemoglobin

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • Hemoglobin (Hb) transports oxygen via heme groups.
  • Ligand entry pathways into Hb are crucial for its function.
  • The E7 channel's role in ligand binding remains debated.

Purpose of the Study:

  • To investigate the role of the E7 channel in human hemoglobin (HbA) ligand binding kinetics.
  • To determine the structural basis for altered CO rebinding rates in Hb mutants.

Main Methods:

  • Site-directed mutagenesis of HbA (His E7 to Trp).
  • Laser photolysis and bimolecular CO rebinding kinetics measurements.
  • X-ray crystallography of mutant Hb and myoglobin (Mb) complexes.

Main Results:

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  • His(E7) to Trp substitutions in HbA caused biphasic CO rebinding.
  • Crystal structures revealed Trp at E7 blocks the E7 channel in Hb and Mb.
  • Blocking or closing the E7 channel dramatically slowed CO binding (1000-fold).

Conclusions:

  • The E7 channel is the primary pathway for ligand entry into human hemoglobin, accounting for at least 90% of binding.
  • Structural data confirms the E7 channel's critical role in modulating ligand access.