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Chapter 5

Chapter 5. Detection of Extracellular signals: the role of receptors. 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. Role of the Receptor. Specificity, only one signal detected

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Chapter 5

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  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 Extracellular Intracellular Gγ Gα Signal propagation Gβ Signal propagation

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

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

  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 Extracellular Hsp56 Hsp70 Cytosol Hsp90 NPC Nucleus DNA Promotor

  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 • 131I, 125I, 3H • Influences • Time, pH, temperature, other ligands present…

  15. Ligand binding to Receptors • How much ligand binds nonspecifically • Compete with unlabeled ligand • Subtract • Kd Total binding Specific binding Nonspecific binding

  16. Scatchard Plot Plot: vs

  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

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