1. Chapter 5 Detection of Extracellular signals: the role of receptors

2. Objectives What are the main types of receptors How to those receptors function in general Why is ligand binding important How do we measure ligand binding

3. Role of the Receptor Specificity, only one signal detected High affinity, usually low concentrations 10 -8 M Must propagate message Must turn off

4. Types of Receptors - G-protein Coupled Receptors GγGγ GβGβ GαGα Signal propagation Extracellular Intracellular

5. –PP– Types of Receptors – Enzyme Activity Extracellular Intracellular

6. Types of Receptors – Ligand Gated Channel Extracellular Intracellular acetylcholine sodium

7. GCPR β2 Adrenergic Receptor

8. GPCR 7 Transmembrane helices Signal through heterotrimeric G-proteins or associated proteins Mediate signaling for hormones, neuropeptides, light, smell, and taste Can involve phosphorylation

9. Ligand Gated Receptors Usually 5 membrane helices Create a channel for ions Rapid open / close Function in neuronal signaling

10. Enzyme Receptors Largest Group Receptor Tyrosine Kinases – Autophosphorylation – Dimers to be active Some Receptors phosphorylate other proteins

11. Intracellular Receptors NPC Hsp56 Hsp70 Hsp 90 Promotor DNA Nucleus Cytosol Extracellular

12. Ligand binding to Receptors Agonist – ligand that binds and activates a receptor Antagonist – ligand that binds receptor but does not activate it Constitutively Active – a receptor that is active in the absence of ligand Consider Ligand/Receptor binding as very similar to Ligand/Protein binding

13. Ligand binding to Receptors Equations:

14. Ligand binding to Receptors How to measure [LR] – Fluorescence labeling Hard to quantify – Radioisotope 131 I, 125 I, 3 H – Influences Time, pH, temperature, other ligands present…

15. Ligand binding to Receptors How much ligand binds nonspecifically – Compete with unlabeled ligand – Subtract K d Total binding Specific binding Nonspecific binding

16. Scatchard Plot

17. Scatchard Plots

18. Receptor Sensitivity Receptor Density – More receptors = better chance of detection – Less receptors = desensitization Clathrin coated vesicles and endocytosis Refractory Response – Homologous desensitization – Heterologous desensitization

19. Homologous desensitization