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Related Concept Videos

G-protein Coupled Receptors01:21

G-protein Coupled Receptors

G-protein coupled receptors are ligand binding receptors that indirectly affect changes in the cell. The actual receptor is a single polypeptide that transverses the cell membrane seven times creating intracellular and extracellular loops. The extracellular loops create a ligand specific pocket which binds to neurotransmitters or hormones. The intracellular loops holds onto the G-protein.
GTPases and their Regulation02:14

GTPases and their Regulation

Guanine nucleotide-binding proteins (G-proteins), also known as GTPases, are a superfamily of proteins that regulate many cellular processes, such as cell signaling, vesicular transport, and the regulation of cell shape and motility. Mutation or dysfunction of these proteins can lead to disease. There are around 40,000 known G-proteins that can broadly be classified into two groups ‒  small G-proteins consisting of a single domain and large multi-domain G-proteins.
Large G-proteins, also known...
GTPases and their Regulation02:14

GTPases and their Regulation

Guanine nucleotide-binding proteins (G-proteins), also known as GTPases, are a superfamily of proteins that regulate many cellular processes, such as cell signaling, vesicular transport, and the regulation of cell shape and motility. Mutation or dysfunction of these proteins can lead to disease. There are around 40,000 known G-proteins that can broadly be classified into two groups ‒  small G-proteins consisting of a single domain and large multi-domain G-proteins.
Large G-proteins, also known...
G Protein-coupled Receptors01:15

G Protein-coupled Receptors

G Protein-Coupled Receptors or GPCRs are membrane-bound receptors that transiently associate with heterotrimeric G proteins and induce an appropriate response to sensory stimuli such as light, odors, hormones, cytokines, or neurotransmitters.
GPCRs are also called heptahelical, 7TM, or serpentine receptors, and consist of seven (H1-H7) transmembrane alpha-helices that span the bilayer to form a cylindrical core. The transmembrane helices are connected by three extracellular loops and three...
Activation and Inactivation of G Proteins01:22

Activation and Inactivation of G Proteins

Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, beta, and gamma. They remain GDP-bound or GTP-bound inside the cells and switch between inactive/active states. The Gα subunit possesses the nucleotide-binding pocket that binds guanine nucleotides and switches between GDP or GTP-bound states. In contrast, the Gꞵ and Gγ subunits are always bound together with high affinity and are together...
GPCRs Regulate Adenylyl Cylase Activity01:09

GPCRs Regulate Adenylyl Cylase Activity

Some GPCRs transmit signals through adenylyl cyclase (AC), a transmembrane enzyme. AC helps synthesize second messenger cyclic adenosine monophosphate (cAMP). AC catalyzes cyclization reaction and converts ATP to cAMP by releasing a pyrophosphate. The pyrophosphate is further hydrolyzed to phosphate by the enzyme pyrophosphatase, which drives cAMP synthesis to completion. However, cAMP is rapidly degraded to 5′ AMP by the enzymes phosphodiesterase (PDE), preventing overstimulation of cells.
Two...

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Comparing the Affinity of GTPase-binding Proteins using Competition Assays
10:37

Comparing the Affinity of GTPase-binding Proteins using Competition Assays

Published on: October 8, 2015

Kinetics versus equilibrium: the importance of GTP in GPCR activation.

I Waelbroeck1

  • 1Laboratoire de Chimie Biologique et de la Nutrition, Faculté de Médecine de l'Université Libre de Bruxelles, Bât. G/E, CP 611, 808 Route de Lennik, B - 1070 Brussels, Belgium. mawaelbro@ulb.ac.be

Trends in Pharmacological Sciences
|December 22, 1999
PubMed
Summary
This summary is machine-generated.

A new steady-state model for G-protein-coupled receptors (GPCRs) explains how agonist potency and efficacy vary with G-protein concentration. This model links agonist efficacy to increased receptor affinity for G proteins, offering a more realistic view of receptor function.

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Last Updated: Jul 8, 2026

Comparing the Affinity of GTPase-binding Proteins using Competition Assays
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Comparing the Affinity of GTPase-binding Proteins using Competition Assays

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Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding
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A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
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A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators

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Area of Science:

  • Biochemistry
  • Pharmacology
  • Molecular Biology

Background:

  • G-protein-coupled receptors (GPCRs) mediate cellular signaling by facilitating GDP-GTP exchange on G proteins.
  • The ternary complex model adequately describes GPCR binding but not their catalytic function.
  • Understanding GPCRs' catalytic role is crucial for drug development and disease research.

Purpose of the Study:

  • To introduce a more realistic steady-state model for agonist-bound GPCRs.
  • To describe the catalytic effect of agonist-bound receptors on G-protein activation.
  • To explain the tissue-specific variations in agonist potency and efficacy.

Main Methods:

  • Development of a steady-state kinetic model for GPCR-G protein interactions.
  • Analysis of the model's predictions regarding agonist potency, efficacy, and G-protein concentration.
  • Extension of the model to incorporate receptor affinity for empty G proteins.

Main Results:

  • The steady-state model predicts that agonist potency and efficacy can vary between tissues based on G-protein concentration.
  • The model demonstrates a relationship between an agonist's efficacy and its ability to enhance receptor affinity for G proteins.
  • This provides a more comprehensive understanding of GPCR signaling dynamics.

Conclusions:

  • A steady-state model offers a more accurate description of agonist-bound GPCRs' catalytic function.
  • G-protein concentration is a key determinant of tissue-specific agonist responses.
  • The model elucidates the link between agonist efficacy and receptor-G protein interaction affinity.