Geometric rules of channel gating inferred from computational models of the P2X receptor transmembrane domain

J Mol Graph Model. 2015 Sep;61:107-14. doi: 10.1016/j.jmgm.2015.06.015. Epub 2015 Jul 9.

Abstract

The P2X receptors are trimeric ATP-gated ion channels and mediate chemical communication between eukaryotic cells. Each P2X subunit contains two transmembrane helices, M1 and M2, and the M2 helix packs around an ion conduction pore. Here, I have reconstructed the three-dimensional models of the zebrafish P2X4 transmembrane domain using spatial restraints on helical packing. The models are stable in lipid bilayers during molecular dynamics simulation and adopt different conformations depending on bilayer hydrophobic thickness. Comparison of these conformations shows that the pore-lining residues L340, A344 and A347 each have multiple packing sites that define the pore configurations. Shift of L340 packing between different sites alters the side-chain orientation that occludes the pore or removes this occlusion. L340, A344 and A347 also gate the pore by expansion-contraction mechanism based on their packing patterns. Finally, pore expansions at the L340 and A344 levels are mutually exclusive, so the P2X gating may involve sequential pore opening at L340 and A344 levels to allow ion conduction. In summary, the current study shows that the computational assembly of the helical membrane protein is not only possible, but also necessary to provide insights into the mechanisms of channel gating.

Keywords: Channel gating; Helical packing; Ion channel; Molecular dynamics; P2X; Transmembrane helix.

MeSH terms

  • Adenosine Triphosphate / chemistry*
  • Amino Acid Motifs
  • Animals
  • Binding Sites
  • Crystallography, X-Ray
  • Hydrophobic and Hydrophilic Interactions
  • Ion Channel Gating*
  • Kinetics
  • Lipid Bilayers / chemistry*
  • Molecular Docking Simulation*
  • Molecular Dynamics Simulation
  • Molecular Sequence Data
  • Phosphatidylcholines / chemistry
  • Protein Binding
  • Protein Multimerization
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Receptors, Purinergic P2X / chemistry*
  • Thermodynamics
  • Zebrafish

Substances

  • Lipid Bilayers
  • Phosphatidylcholines
  • Receptors, Purinergic P2X
  • 1,2-linoleoylphosphatidylcholine
  • 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine
  • Adenosine Triphosphate
  • 1-palmitoyl-2-oleoylphosphatidylcholine