Introduction to Receptors

1
Introduction to Receptors

• Tim Bloom, Ph.D.
• Room 104A Hall of Science
• 893-1712
• bloom_at_campbell.edu
• www.campbell.edu/faculty/bloom

2
Lecture Overview

• History of receptors
• Receptor theory
• Biochemistry of receptors
• Examples of common receptor types

3
Pharmacology

• Pharmacokinetics
• Absorption
• Distribution
• Metabolism
• Excretion

• Pharmacodynamics
• Receptors
• Signaling

4
Berthold and the Roosters

• Effects of castration
• Secondary sex characteristics
• Behavior
• Effects of transplant
• Observation and hypothesis

5
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
• Stimulate ion entry into cell
• 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 act as ligands
• SH2 proteins recognize Tyr-P and bind
• Binding activates SH2 proteins
• Creation of signaling complex

23
Signaling Complex
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
G protein-coupled Receptors

• Differ from other classes
• Seven transmembrane domains
• No activity of its own
• All act through combination of G proteins and
  effector proteins

E
G
R
B
A
26
G Proteins

• Made of three subunits a, b, g
• b, g act to inhibit a
• a has three functions
• Detects ligand-bound receptor (gets active)
• Activates effector
• Turns itself off

a
b
g
GDP
27
Cycle of the a Subunit

• 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

R
a
bg
GDP
a
GTP
a
GDP
E
a
GTP
28
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

29
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