G-protein coupled receptors

Definition

G-protein coupled receptors (GPCRs) are a large family of membrane proteins that play a crucial role in cellular signaling by transmitting signals from outside the cell to the inside. These receptors are activated by various ligands, such as hormones, neurotransmitters, and environmental stimuli, which leads to a conformational change in the receptor and activates an associated G-protein. This activation triggers a cascade of intracellular responses, influencing various physiological processes like vision, taste, and immune response.

5 Must Know Facts For Your Next Test

1. GPCRs are the largest family of cell surface receptors, with over 800 different types identified in humans.
2. They are involved in many physiological processes and are the target for around 30% of all modern medicinal drugs.
3. Upon ligand binding, GPCRs activate G-proteins by exchanging GDP for GTP, leading to the dissociation of G-protein subunits that activate downstream effectors.
4. The signaling pathways initiated by GPCRs can involve second messengers like cyclic AMP (cAMP) or inositol triphosphate (IP3), which further amplify the signal inside the cell.
5. GPCRs can also undergo desensitization, where prolonged exposure to a ligand decreases the receptor's responsiveness, helping cells adapt to persistent signals.

Review Questions

• How do G-protein coupled receptors contribute to the process of signal transduction in cells?
  • G-protein coupled receptors initiate signal transduction by binding specific ligands on the cell surface. Once activated by ligand binding, GPCRs undergo a conformational change that activates an associated G-protein by facilitating the exchange of GDP for GTP. This activation causes the G-protein to dissociate into its subunits, which then interact with various intracellular effectors, leading to changes in cellular activity and the generation of second messengers that amplify the signal.
• Discuss the significance of GPCRs as drug targets in modern medicine and how they relate to therapeutic interventions.
  • GPCRs are significant drug targets due to their involvement in numerous physiological processes and their accessibility on cell surfaces. Approximately 30% of modern medicinal drugs target GPCRs to treat various conditions such as hypertension, depression, and allergies. By modulating the activity of specific GPCRs, these drugs can effectively alter signaling pathways associated with diseases, highlighting their importance in developing effective therapeutic interventions and improving patient outcomes.
• Evaluate the impact of GPCR desensitization on cellular signaling and how this mechanism contributes to cellular homeostasis.
  • GPCR desensitization is a crucial mechanism that helps maintain cellular homeostasis by preventing overstimulation from persistent signals. When GPCRs are continuously activated by high levels of ligands, they undergo modifications that reduce their responsiveness. This desensitization ensures that cells can adapt to changing environments and prevents excessive cellular responses that could lead to dysfunction or damage. Understanding this process is essential for developing therapies aimed at modulating GPCR activity in disease contexts.

Related terms

Ligand: A molecule that binds to a receptor, initiating a cellular response. Ligands can be hormones, neurotransmitters, or other signaling molecules.

Second Messenger: Intracellular signaling molecules released in response to receptor activation that amplify the signal and trigger further cellular responses.

Signal Transduction: The process by which a cell converts an external signal into a functional response, often involving multiple steps and signaling molecules.