Structure and rearrangements in the carboxy-terminal region of SpIH channels

Structure. 2007 Jun;15(6):671-82. doi: 10.1016/j.str.2007.04.008.


Hyperpolarization-activated cyclic nucleotide-modulated (HCN) ion channels regulate the spontaneous firing activity and electrical excitability of many cardiac and neuronal cells. The modulation of HCN channel opening by the direct binding of cAMP underlies many physiological processes such as the autonomic regulation of the heart rate. Here we use a combination of X-ray crystallography and electrophysiology to study the allosteric mechanism for cAMP modulation of HCN channels. SpIH is an invertebrate HCN channel that is activated fully by cAMP, but only partially by cGMP. We exploited the partial agonist action of cGMP on SpIH to reveal the molecular mechanism for cGMP specificity of many cyclic nucleotide-regulated enzymes. Our results also elaborate a mechanism for the allosteric conformational change in the cyclic nucleotide-binding domain and a mechanism for partial agonist action. These mechanisms will likely extend to other cyclic nucleotide-regulated channels and enzymes as well.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation
  • Amino Acid Substitution
  • Animals
  • Carrier Proteins / metabolism
  • Crystallography, X-Ray
  • Cyclic AMP / chemistry
  • Cyclic AMP / metabolism
  • Cyclic AMP / pharmacology
  • Cyclic GMP / metabolism
  • Cyclic GMP / pharmacology
  • Cyclic Nucleotide-Gated Cation Channels
  • DNA, Complementary / genetics
  • Dose-Response Relationship, Drug
  • Female
  • Hydrogen Bonding
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Ion Channel Gating
  • Ligands
  • Microinjections
  • Models, Biological
  • Models, Chemical
  • Models, Molecular
  • Oocytes / cytology
  • Oocytes / physiology
  • Patch-Clamp Techniques
  • Potassium Channels / agonists
  • Potassium Channels / chemistry*
  • Potassium Channels / genetics
  • Potassium Channels / metabolism*
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • RNA, Messenger / metabolism
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Valine / metabolism
  • Xenopus


  • Carrier Proteins
  • Cyclic Nucleotide-Gated Cation Channels
  • DNA, Complementary
  • Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels
  • Ligands
  • Potassium Channels
  • Protein Subunits
  • RNA, Messenger
  • Recombinant Fusion Proteins
  • Cyclic AMP
  • Cyclic GMP
  • Valine

Associated data

  • PDB/2PTM
  • PDB/2Q0A