G protein coupled receptor

Description of GPCR
structure
second messenger pathway
recent advances

1. G-PROTEIN COUPLED RECEPTOR Moderator Dr . Dilshad Ali Rizvi Fardan Qadeer JR II

2. OVERVIEW: WHAT ARE RECEPTORS TYPES OF RECEPTORS G PROTEIN COUPLED RECEPTORS STRUCTURE OF GPCR SINGNAL TRANSDUCER MECHANISM SECOND MESSENGERS RECENT ADVANCES

3. RECEPTOR: Any target molecule with which a drug molecule has to combine in order to elicit its specific effect A major group of drug receptors consists of proteins that normally serve as receptors for endogenous regulatory ligands.

4. Type 1: ligand-gated ion channels Type 2: G-protein-coupled receptors Type 3: receptor kinases Type 4: nuclear receptors Location Membrane Membrane Membrane Intracellular Effector Ion channel Channel or enzyme Protein kinases Gene transcription Time frame Milliseconds Seconds Hours Hours Examples Nicotinic acetylcholine receptor, GABA A receptor Muscarinic acetylcholine receptor, adrenoceptors Insulin, growth factors, cytokine receptors Steroid receptors Structure Oligomeric assembly of subunits surrounding central pore Monomeric or oligomeric assembly of subunits comprising seven transmembrane helices with intracellular G-protein-coupling domain Single transmembrane helix linking extracellular receptor domain to intracellular kinase domain Monomeric structure with separate receptor- and DNA-binding domains

5. Humans express over 800 GPCRs that make up the third largest family of genes in humans. Majority of these are involved in sensory perception and the remaining receptors regulate various physiological functions including nerve activity, tension of smooth muscle, metabolism, rate and force of cardiac contraction, and the glandular secretion. GPCRs are the targets for many drugs; perhaps half of all non-antibiotic prescription drugs act at these receptors.

6. Netter’s illustrated pharmacology Selected G Protein Coupled Receptor/Ligands Hormones Thyroid hormone Parathyroid hormone FSH Vasopressin LH ACTH Glucagon Autocoids: Histamine 5-HT Leukotrienes Bradykinin Autonomic Nervous Control: Muscarinic Cholinergic Receptors Epinephrine Others: Angiotensin Melatonin Adenosine Dopamine Glutamate Neuropeptide Y GABA Somatostatins Opioids

7. Structure: GPCRs share a common structural signature of seven hydrophobic transmembrane segments , with an extracellular amino terminus and an intracellular carboxyl terminus Netter’s illustrated pharmacology

8. Netter’s illustrated Pharmacology

9. A:Rhodopsin family: Short extracellular (N terminal) tail. Ligand binds to transmembrane helices (amines) or to extracellular loops (peptides) The largest group. Receptors for most amine neurotransmitters, many neuropeptides , purines prostanoids cannabinoids

10. B:Secretin/glucagon receptor family: Receptors for peptide hormones secretin glucagon calcitonin Intermediate extracellular tail incorporating ligand-binding domain

11. C:Metabotropic glutamate receptor/ calcium sensor family Smallest group Metabotropic glutamate receptors GABA B receptors Ca 2 + -sensing receptors Long extracellular tail incorporating ligand-binding domain

12. The transducer mechanism Ligand receptor interaction Second Messenger pathway Protein activation

13. Rang et al: Rang & Dale’s Pharmacology 7e

14. G-protein subunits with second messenger β γ α G s G i G q cAMP stimulation β receptor Histamine Serotonin Dopamine cAMP inhibition α 2 receptor M 2 receptor Opioid receptor D 2 receptor 5HT 1 receptor PLC (IP 3 & DAG) α 1 M 1 AT 1 5HT 2 Vasopressin Activate potassium channels • Inhibit voltage-gated calcium channels • A ctivate mitogen-activated protein kinase cascade .

15. The adenylyl cyclase system cAMP is a nucleotide Synthesized within the cell from ATP by membrane-bound, adenylyl cyclase Produced continuously Inactivated by hydrolysis to 5´-AMP, by the Phosphodiesterase Common mechanism, namely the activation of protein kinases

16. Effect of Glycogen on the muscle cell Rang et al: Rang & Dale’s Pharmacology 7e

17. Netter’s illustrated pharmacology

18. Phosphodiesterase Theophylline Caffine Rolipram Sildenafil

19. Phospholipase-c signaling system PIP 2 IP 3 DAG Release of Ca +2 from ER  intracellular C a +2 Along with C a +2 Activate Protein Kinase-C Cellular functions- Proliferation, differentiation, apoptosis, cytoskeletal Remodeling, vesicular trafficking, ion channels conductance, neurotransmission PLC

20. C Ca

21. Targets that act through PLC and IP3 Acetylcholine M1 Glutamate Platelet derived growth factor Angiotensin II Vasopressin Serotonin 5 HT 2C Oxytocin Histamine H1 GnRH α 1 Adrenergic agonist Rang et al: Rang & Dale’s Pharmacology 7e

22. Effect of Toxins Gα s Activated by cholera toxin which blocks GTPase activity Gα i Blocked by pertussis toxin and prevents dissociation of αβϒ complex Gα o? Blocked by pertussis toxin Rang et al: Rang & Dale’s Pharmacology 7e

23. G protein gated Ion Channels G-protein-coupled receptors can control ion channel function directly. Typically , the activated effector protein begins a signaling cascade which leads to the eventual opening of the ion channel. The GTP-bound α-subunit i n some cases can directly activate the ion channel. In other cases, the activated βγ-complex of the G protein may interact with the ion channel.

24. Increase Ca++ Decrease Ca++ Increase K+ Adrenergic β 1 ( Heart) Dopamine D2 Adrenergic α 2 Adenosine A1 Muscarinic M2 GABA-B Dopamine D2 Somatostatin 5-HT 1A Opioid K GABA B

25. Receptor desensitization Often, the effect of a drug gradually diminishes when it is given continuously or repeatedly change in receptors translocation of receptors exhaustion of mediators increased metabolic degradation of the drug physiological adaptation active extrusion of drug from cells

26. Rang et al: Rang & Dale’s Pharmacology 7e

27. Recent advances

28. Orphan GPCRs 200 or so known GPCRs whose endogenous ligands and functions are not known Attempts have been made to deorphanise these receptors Evidence that some recently deorphanised GPCRs, such as orexin receptor, may dimerise or associate with more classical GPCRs

29. British Journal of Pharmacology (2008) 153 S339–S346

30. GPCR mutations, disease and novel drug discovery Loss of function mutations in GPCRs involved in the control of endocrine systems G ain of function mutations in GPCRs also cause disease  Mutations in GPCRs could be responsible for variations in drug sensitivities among different populations

31. mAbs 2:6, 594-606; November/December 2010; © 2010 Landes Bioscience