CT-Pharm Lecture slides 3_2024NOW

Understanding G-Protein Coupled Receptors (GPCRs)

  • GPCRs are a large family of cell surface receptors that play crucial roles in transmitting signals from outside the cell to its interior.

  • They are involved in various physiological processes, including sensory perception, immune responses, and neurotransmission.

Learning Outcomes

At the end of this session, you should:

  • Understand the structure and function of GPCRs.

  • Be able to describe the activation signal transduction pathways of GPCRs.

  • Explain methods to study GPCR dimerization.

Techniques to Study GPCR Dimerization

Biochemical Techniques

  • Differential Epitope Tagging: Used to study specific interactions and dimerization involving receptors.

    • Example: β2-adrenoceptor tagged with various epitopes.

Biophysical Techniques

  • Bioluminescence Resonance Energy Transfer (BRET): Monitors protein interactions in live cells.

    • Useful for detecting β2-adrenergic receptor dimers in real-time.

  • Fluorescence Resonance Energy Transfer (FRET): Similar approach using fluorescent proteins to measure proximity.

  • Bimolecular Fluorescence Complementation (BiFC): Used to visualize receptor interactions in cells by reconstituting the fluorescent protein.

  • Bimolecular Luminescence Complementation (BiLC): Combines luminescence and fluorescence techniques.

Generation of Expression Plasmids

  • Constructing Plasmids:

    • Incorporate sequences for epitope tags (e.g., HA tag) into the β2-AR plasmid.

    • Cut using restriction enzymes and ligate to create expression plasmids.

  • Transfection Process: Cells are transfected with plasmids to express epitope-tagged receptors, allowing for observation of receptor interactions.

TMVI Peptide Role in Dimerization

  • TMVI Peptide: Sequence from the β2-adrenergic receptor that can influence its dimerization.

    • The peptide contains a transmembrane domain crucial for receptor interactions.

  • Study Findings:

    • Application of TMVI peptide reduces dimerization and receptor activation, indicating its inhibitory role.

Analysis of β2AR Dimerization

  • Homodimerization vs. Monomers: Research studies show how the β2AR can exist as homodimers or separate monomers and the effects of ligand binding (e.g., isoproterenol) on this dynamic.

Techniques for Visualization of GPCR Dimers

BRET and FRET

  • BRET: Involves transferring energy between luciferase (donor) and fluorescent protein (acceptor), providing insight into GPCR interactions.

  • FRET: Uses variations of fluorescent proteins like YFP and CFP to detect close proximity of GPCRs, allowing for visualization of dimerization.

Experimental Considerations

  • Important to check pharmacology and signaling properties when using constructs like β2-AR fused with luminescent proteins.

  • Distance between donor and acceptor proteins affects the efficiency of BRET; typically needs to be between 10-100 Å.

Homodimerization and Agonist Activity

  • Agonists can lead to different levels of homodimerization, impacting various GPCRs such as the β2-adrenergic receptor, which is necessary for Gs coupling and signaling.

Suggested Reading

  • Key references include publications by Hebert et al. exploring the roles of GPCR dimerization, methods for studying GPCRs, and pharmacological implications of receptor interactions.

Questions for Reflection

  1. Describe the methods SDS-PAGE, Western blotting, and immunoprecipitation.

  2. Discuss the significance of differential epitope tagging in GPCR research.

  3. Explain the relevance of BRET and FRET techniques in studying GPCR dimerization.