Inhibition of GDP/GTP exchange on G alpha subunits by proteins containing G-protein regulatory motifs

Biochemistry. 2001 May 1;40(17):5322-8. doi: 10.1021/bi015505w.


A novel Galpha binding consensus sequence, termed G-protein regulatory (GPR) or GoLoco motif, has been identified in a growing number of proteins, which are thought to modulate G-protein signaling. Alternative roles of GPR proteins as nucleotide exchange factors or as GDP dissociation inhibitors for Galpha have been proposed. We investigated the modulation of the GDP/GTP exchange of Gialpha(1), Goalpha, and Gsalpha by three proteins containing GPR motifs (GPR proteins), LGN-585-642, Pcp2, and RapIGAPII-23-131, to elucidate the mechanisms of GPR protein function. The GPR proteins displayed similar patterns of interaction with Gialpha(1) with the following order of affinities: Gialpha(1)GDP >> Gialpha(1)GDPAlF(4)(-) > or = Gialpha(1)GTPgammaS. No detectable binding of the GPR proteins to Gsalpha was observed. LGN-585-642, Pcp2, and RapIGAPII-23-131 inhibited the rates of spontaneous GTPgammaS binding and blocked GDP release from Gialpha(1) and Goalpha. The inhibitory effects of the GPR proteins on Gialpha(1) were significantly more potent, indicating that Gi might be a preferred target for these modulators. Our results suggest that GPR proteins are potent GDP dissociation inhibitors for Gialpha-like Galpha subunits in vitro, and in this capacity they may inhibit GPCR/Gi protein signaling in vivo.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Binding, Competitive
  • Cloning, Molecular
  • Fluorescent Dyes / metabolism
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism
  • GTP-Binding Protein beta Subunits*
  • GTP-Binding Protein gamma Subunits*
  • Guanine Nucleotide Dissociation Inhibitors / chemistry
  • Guanine Nucleotide Dissociation Inhibitors / physiology*
  • Guanine Nucleotide Exchange Factors / antagonists & inhibitors*
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Guanosine Diphosphate / antagonists & inhibitors
  • Guanosine Diphosphate / metabolism*
  • Guanosine Triphosphate / antagonists & inhibitors
  • Guanosine Triphosphate / metabolism*
  • Heterotrimeric GTP-Binding Proteins / metabolism
  • Humans
  • Mice
  • Molecular Sequence Data
  • Neuropeptides / genetics
  • Neuropeptides / isolation & purification
  • Neuropeptides / metabolism
  • Protein Binding
  • Protein Conformation
  • Rats


  • Fluorescent Dyes
  • G-protein Beta gamma
  • GTP-Binding Protein beta Subunits
  • GTP-Binding Protein gamma Subunits
  • Guanine Nucleotide Dissociation Inhibitors
  • Guanine Nucleotide Exchange Factors
  • Neuropeptides
  • Pcp2 protein, mouse
  • Guanosine Diphosphate
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Guanosine Triphosphate
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • Heterotrimeric GTP-Binding Proteins