Lecture 6 (Drug Targets) Flashcards
To types of drug targets?
1) receptors
2) enzymes
What are receptors responsible for?
transmitting a signal to a cell
What are enzymes responsible for?
catalyze biochemical reactions
List example of receptors
- GPCR’s (G-protein couple receptors)
- voltage gated ion channels
- ligand gated ion channels
- nuclear hormone receptors
List some different kinds of enzymes
- soluble enzymes
- transmembrane or membrane bound enzymes
How do voltage gated ion channels work?
- depolarization causes ion channel to open
- hyper polarization causes ion channel to close
How do drugs typically affect a voltage-gate ion channel?
A drug binds to the ion channel and typically inhibits its function
T or F: binding can occur on intracellular or extracellular part of the ion channel (voltage gated)
True
T of R: binding can not occur on the inside of the pore
False
binding can occur within the pore of the channel itself or on the outside
List some examples of binders to voltage gated ion channels
- local anesthetics
- calcium channel blockers
- class 1 and 3 antiarrhythmics
How do ligand gated ion channels work?
a ligand binds to the channel and triggers a conformational change which opens the ion channel
Where is the receptor binding site normally found for ligand gated ion channels?
on the outside of the membrane
Examples of agonists (ligands) that bind to ligand gated ion channels
nicotine
acetylcholine
GABA A
AMPA receptors
Explain how nuclear hormone receptors work
- ligand diffuses across cell membrane
- diffuses into nucleus
- binds to nuclear hormone receptor
-then it binds to RE (response element which is some specific sequence of DNA)-this is the promoter of the gene so therefore transcription of the gene will change
**obvs these ligands have to be lipophilic because they have to cross lipid membranes
Describe the two parts to nuclear receptors:
DBD (DNA binding domain) - binds to DNA
LBD (ligand binding domain) - binds to nuclear hormone (ligand)
Receptor for estradiol
estrogen receptor (ER)
receptor for testosterone
androgen receptor
receptor for progesterone
progesterone receptor
receptor for cortisol
glucocorticoid receptor
Other receptor:
mineralocorticoid receptor
receptor for aldosterone
mineralocorticoid receptor
Other receptor: glucocorticoid receptor (weak)
receptor for Vitamin A
retinoic acid receptor
receptor for Vitamin D
vitamin D receptor
thyroid hormone
thyroid hormone (T3, T4) receptor
Describe transmembrane enzymes
-these are a group of receptors that have an extracellular ligand binding domain and an intracellular enzymatic domain within the same protein.
examples of transmembrane enzymes ?
- EGF (epidermal growth factor)
- insulin receptors which contain intrinsic tyrosine kinases in the cytoplasmic domain
What does tyrosine kinase do?
adds phosphate to tyrosine
What does EGFR do?
it’s a transmembrane receptor tyrosine kinases which is needed for the growth and differentiation of epithelial cells.
over expression of EGFR is found in epithelial cancers.
What can phosphotyrosine bind to?
proteins with an SH2 doamins
What does RAS activate?
RAS activates a protein kinase cascade called the mitogen-activated protein kinase pathway (MAPK)
What does the kinase result in?
it results in phosphorylation of a number of transcription factors in the nucleus, including the cAMP response element-binding protein (CREB)
*see slide 14
For enzymes the equivalent of an antagonist is an ____
inhibitor
The equivalent of an agonist would be another ____
substrate
**although this is almost never the goal of drug discovery
______ help catalyze rxns from substrate to product
enzymes
What does GPCR stand for?
G-protein coupled receptor
Describe GPCRs
- probably the most important group of receptors
- target for about 45% of drugs on the market
What are the 3 components of GPCRs?
- receptor on outside of membrane binds ligand
- G-protein on inside of membrane senses signal from ligand-receptor interaction
- effector protein - binds G-protein and produces or inhibits production of a second messenger
Describe the structure of a GPCR
- large protein that spans the membrane
- 7 alpha helices that cross membrane = 7 transmembrane helix receptors
- ligand binding on extracellular sie
- g-protein (signalling protein) is on intracellular side
What can the G-protein bind?
GDP
GTP
What 3 subunits does a G-protein have?
alpha
beta
gamma
understand slide 18
okay
G alpha s (stimulatory)
it activates AC (adenylate cyclase) and opens calcium channels leading out of the cell
G alpha s (stimulatory)
second messenger?
cAMP produced
G alpha i (inhibitory)
inhibits AC (adenylate cyclase) and opens K+ channels
G alpha i (inhibitory)
second messenger?
cAMP inhibited
Go
activates receptors that inhibit calcium ion channels leading out of the cell
*inhibit calcium ion channels
G alpha q
actives PLC B (phospholipase C beta)
G alpha q
second messenger?
DAG and IP3 produced
look at slide 20
okay
adenylate cyclase (AC) produces what?
Ppi and cAMP
The active site of AC is blocked until ?
G alpha s binds (which allows ATP to enter)
What are some effects of AC activity
increased glucose
decreased glycogen synthesis
increased lipolysis
*slide 22
(all through phosphorylation)
Describe G alpha i
- cAMP production is being inhibited.
- therefore PKA remains inactive
*then the beta gamma subunits also opens a K+ channel which results in hyper polarization of membrane (K can leave the cell)
Describe G alpha q
membrane bound PLC B binds G alpha q and PLC B is activated
PLC B hydrolyzes phosphatidylinositol diphosphate (PIP2) to second messengers diacylglycerol (DAG) and inositol triphosphate (IP3)
*PLC B activated
which turns
PIP2 into
DAG and IP3
____ is bound to the membrane
PLC B
___ is a phospholipid found in membrane
PIP2
___ being hydrophobic stays in the membrane
DAG
___ is a hydrophilic molecule and stays in cytosol
IP3
Gaq results in an increase in ?
intracellular calcium
What does the calcium produced do?
calcium also binds to calmodulin (CaMCa) and stimulates PDE which hydrolyzes cAMP to 5’AMP
*this counteracts the signal from G alpha s
see slide 26 for diagram
AC and G alpha s ___ intracellular calcium
decrease!!!
What does the decrease in intracellular calcium do?
it counteracts the effects of G alpha q
