Phosphatidylinositol 3,4,5-trisphosphate and Ca2+/calmodulin competitively bind to the regulators of G-protein-signalling (RGS) domain of RGS4 and reciprocally regulate its action

Biochem J. 2005 Jan 1;385(Pt 1):65-73. doi: 10.1042/BJ20040404.


RGS (regulators of G-protein signalling) are a diverse group of proteins, which accelerate intrinsic GTP hydrolysis on heterotrimeric G-protein a subunits. They are involved in the control of a physiological behaviour known as 'relaxation' of G-protein-gated K+ channels in cardiac myocytes. The GTPase-accelerating activity of cardiac RGS proteins, such as RGS4, is inhibited by PtdIns(3,4,5)P3 (phosphatidylinositol 3,4,5-trisphosphate) and this inhibition is cancelled by Ca2+/calmodulin (CaM) formed during membrane depolarization. G-protein-gated K+ channel activity decreases on depolarization owing to the facilitation of GTPase-activating protein activity by RGS proteins and vice versa on hyperpolarization. The molecular mechanism responsible for this reciprocal control of RGS action by PtdIns(3,4,5)P3 and Ca2+/CaM, however, has not been fully elucidated. Using lipid-protein co-sedimentation assay and surface plasmon resonance measurements, we show in the present study that the control of the GTPase-accelerating activity of the RGS4 protein is achieved through the competitive binding of PtdIns(3,4,5)P3 and Ca2+/CaM within its RGS domain. Competitive binding occurs exclusively within the RGS domain and involves a cluster of positively charged residues located on the surface opposite to the Ga interaction site. In the RGS proteins conserving these residues, the reciprocal regulation by PtdIns(3,4,5)P3 and Ca2+/CaM may be important for their physiological regulation of G-protein signalling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / pharmacology
  • Amino Acid Sequence
  • Amino Acid Substitution / genetics
  • Animals
  • Binding, Competitive
  • Calcium / metabolism*
  • Calcium / pharmacology
  • Calmodulin / metabolism*
  • Calmodulin / pharmacology
  • Cattle
  • Circular Dichroism
  • Electric Conductivity
  • Electron Spin Resonance Spectroscopy
  • GTP-Binding Protein alpha Subunits / metabolism
  • Lysine / genetics
  • Lysine / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Oocytes / drug effects
  • Oocytes / metabolism
  • Phosphatidylinositol Phosphates / metabolism*
  • Potassium Channels / metabolism
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Tertiary
  • RGS Proteins / chemistry*
  • RGS Proteins / metabolism*
  • Substrate Specificity
  • Xenopus


  • Calmodulin
  • GTP-Binding Protein alpha Subunits
  • Phosphatidylinositol Phosphates
  • Potassium Channels
  • RGS Proteins
  • phosphatidylinositol 3,4,5-triphosphate
  • RGS4 protein
  • Lysine
  • Acetylcholine
  • Calcium