Introduction to Receptors

1. Introduction to Receptors Tim Bloom, Ph.D. Room 206 Maddox Hall 893-1712 bloom@campbell.edu www.campbell.edu/faculty/bloom

2. Lecture Overview • History of receptors • Receptor theory • Biochemistry of receptors • Examples of common receptor types

3. Pharmacokinetics Absorption Distribution Metabolism Excretion Pharmacodynamics Receptors Signaling Pharmacology

4. Berthold and the Roosters • Effects of castration • Secondary sex characteristics • Behavior • Effects of transplant • Observation and hypothesis

5. flow in flow out Isolated Muscle Setup rise in tension rise in tension rise in tension nicotine

6. Langley and the Frogs • In vitro study with leg muscle strips • Muscle stimulation by • Electricity • Nerve • Nicotine • Effect of curare on animals • Effect of curare on in vitro muscle stimulation • Electricity into nerve • Nicotine • Electricity into muscle

7. Ehrlich and the Parasites • Organic chemist making clothing dyes • Saw dyeing of cells with selective stains • Staining a cell type is dye-dependent • Small changes in chemical alter staining • “Receptive substance” on cells • Use as target for selective drugs • Attach toxin to selective dye

8. Sum of History • Chemicals affect tissues • Some chemicals interfere with others • Chemical structure impacts action • Cells produce chemicals that affect other cells • Therefore, cells can detect chemicals

9. Receptor Theory • Core of pharmacodynamics • Cells have “receptors” • Act as targets for “ligands” (drugs, hormones, neurotransmitters, etc.) • Required for biological effect of above agents • Sensitive to small changes in ligand structure • Mediate action of ligand • NO RECEPTOR = NO RESPONSE

10. Biochemistry of Receptors • Chemical receptors • Non-specific • Bind via one or two chemical bonds • Examples are stomach acid, heavy metals • Macromolecular receptors • Detect specific molecules • Require multiple chemical bonds • Rely on 3-D shape of ligand for recognition • These are of interest to pharmacologists

11. Molecules as Receptors • DNA • Alkylating chemicals as cancer chemotherapy • DNA damage gives therapeutic result • Structural proteins • Colchicine • Interferes with tubulin polymerization • Enzymes • NSAIDs • Inhibit cyclo-oxygenase

12. Molecules as Receptors • Ion channels • Nicotine • Allow ions to cross cell membranes • Transcription factors • Steroid hormones • Alter rates of gene expression up or down • Plasma membrane signaling proteins • Insulin or adrenaline • Binding results in a signal detected inside cell

13. Importance of Bonds • Chemical bonds are formed between a receptor and its ligand(s) • Hydrogen bonds • Hydrophobic interactions • Van der Waals forces • Ionic bonds • (covalent bonds)

14. Bonds for Activity • Ability to create proper bonds is vital • Proper bonds possible with proper shape • Bonds allow “proper” interactions • Small modifications can have large effect • Weak bonds = temporary binding

15. Receptor Functions • Most common is to generate a “signal” • Alters some facet of cell balance • “Signal” results in some cellular change • Basal cell at rest has certain features: • Stable pH and electrical charge (ion concentrations) • Stable transcription rates • Stable levels of signaling molecules • Stable levels of protein modifications • Stable metabolic rate

16. Signaling Receptor Classes • Four major classes of signaling receptors • Cytoplasmic transcription factors • Ion channels • Transmembrane signaling enzymes • G-protein coupled receptors

17. Cytoplasmic Transcription Factors • Inactive at rest • Bound to inhibitor protein • Ligand removes inhibitor • L-R complex moves to nucleus • Transcription is altered

18. Ion Channels • Made up of subunits • Group forms a pore • Gate blocks ions • Ligand binding affects gate behavior • Some ligands activate channel, let ions flow

19. Transmembrane Enzymes • Receptor is single protein • Dimerization required for activity • Inactive at rest, activated by ligand • Most common type is tyrosine kinase

20. Tyrosine Kinases • Kinases transfer phosphates (phosphorylation) • From ATP to proteins • Addition to serine, threonine or tyrosine • Modifies substrate protein activity • Activate • Inactivate • Alters interactions with other proteins

21. Kinase Receptors • These receptors have tyrosine kinase activity • Phosphorylate substrate proteins, including other receptor in dimer • Receptor phosphorylation makes it active: even without ligand!

22. Kinase receptors • Phosphorylated receptors also act as ligands • “SH2 proteins” recognize Tyr-P and bind • Binding activates SH2 proteins • Creation of signaling complex

23. substrate product Example PLC-g kinase P04 SH2 protein

24. G protein-coupled Receptors • Largest class of receptors • Wide range of ligands • Wide range of binding “methods”

25. Differ from other classes Seven transmembrane domains All act through combination of G protein and effector protein G protein-coupled Receptors E G R B A

26. Made of three subunits: a, b, g a has three functions: Detects ligand-bound receptor (gets active) Activates effector Turns itself off G Proteins a b g GDP

27. Activated by ligand- bound receptor Swaps GDP for GTP Loses b,g subunits Activates effector Hydrolyzes GTP to GDP- is inactivated Rebinds b,g subunits Cycle of the a Subunit R* a bg GDP a GTP a GDP E a GTP

28. Effectors • Enzymes • Synthesize product when activated • Modify proteins when active • Ion channels • Ions flow down gradient • Change in electrical state • Activated effectors produce effects

29. Review • Cells respond to substances via receptors • Receptors provide two functions • Detect ligand presence • Generate a signal in response to ligand • (signal = change) • Signaling through receptor modifies cell • Most cellular molecules can be a receptor

30. Review • Many receptors are in one of four classes • Ion channels • Transcription factors • Membrane-associated enzymes • G-protein coupled receptors • Normal function of a receptor determines the nature of its signal