PPT 2 Flashcards
Unit 1
What are the 3 factors in receptor concept
- Receptors determine relations between dose/concentration of drug and pharmacologic effects (receptor affinity (Kd) determines dose)
- Receptors are responsible for selectivity of drug action
- Receptors mediate actions of agonists and antagonists
What are orphan receptors?
Receptors that have been identified but we don’t know what binds to it (no known endogenous ligand)
What are the 3 components of cell signaling?
- Signal
- Receptor
- Effector
If secondary messaging - also has signal transduction proteins and secondary messengers
What are the 2 consequences of hormones regulating gene expression?
Lag period - time it takes to make new proteins
Persistence (effects can continue for hours-days)
Where can receptor proteins be located?
In the cell or cell membrane
Define coupling
the overall transduction process that links drug occupancy of receptors and pharmacologic response
How is the efficiency of coupling determined?
Conformational change, downstream cellular response, and dose response (number of receptors bound - linear, or strength of signal transduction cascade - multiplied response)
Describe the phosphorylation cascade
Ligand binding → Receptor activation (change of conformation) → First protein (kinase) activation → Subsequent protein (kinase) activation (amplification) → Effector protein activation → Cellular response
What are the 5 mechanisms of transmembrane signaling?
- Lipid soluble - intracellular
- Enzymatic activity allosteric
- Catalytic
- Ion channels
- GPCRs
What binds to the alpha portion of the G protein ?
Guanine nucleotide (GTP) - active or GDP (inactive)
What makes G-proteins trimeric?
3 different amino acid strands that function together to form G-protein
Alpha - binds to GDP (inactive) or GTP (active)
Beta and gamma - help binding to receptor itself
What receptors are intracellular?
Lipid soluble - uncharged
Gasses - easily diffuses through membrane
What is the motif of every GPCR?
Have 7 trans-membrane alpha helices
What are the steps to the GPCR cascade?
- Drug binds to receptor - activates alpha subunit of G protein (conformation change)
- G protein releases GDP and binds GTP
- G protein activates effector protein
- Secondary messenger cascade or ion conductance
What makes a GPCR response fast vs slow?
Fast - rapid desensitization, metabotropic ion channels
Slow - secondary messenger (transcription factor activation)
What is the most important part of the G protein?
Alpha subunit - activates effector
Differentiate between desensitization and resensitization
- When first give agonist, response jumps up, peaks, then declines (muted response with same amount of agonist) - desensitization
- Stop giving agonist, then wait, then give agonist again → see same response - resensitization
Describe the steps to the desensitization process
- Drug binds to receptor → promotes receptor interaction with G proteins in cytoplasm (closed → open conformation)
- Agonist-activated receptors phosphorylated by G protein-coupled receptor kinase (GPK), preventing receptor interaction with G protein → attracts beta-arestin (B-Arr)
- B-Arr receptor complex binds to coated pits, promoting receptor internalization
- 2 possibilities:
Possibility 1 - resensitization (Drug falls off receptor→ phosphatase dephosphorylates receptor and receptor recyles back to cell membrane)
Possibility 2 → degradation (Can’t get drug off of receptor → lysosome merges with drug/receptor complex → enzymes from lysosome degrade receptor)
Why would a receptor be degraded instead of resensitized (recycled)?
Repeated or prolonged exposure of cells to agonist favors degradation → promoting receptor down-regulation rather than resensitization
How does beta-arestin work?
Beta-arestin is a protein that binds to -OH groups when receptor in open conformation for long time (prolonged binding - i.e. covalent bonds) and binds to coated pits, preventing G protein from rebinding
How does the coated pit engulf the receptor complex?
Clathrin coated pit (endocytosis) drags whole receptor with bound drug and beta-arestin into cell
Differentiate between kinase and phosphatase
Kinase attaches phosphate group to protein
Phosphatase strips away phosphate group from protein
How do RTKs work?
Receptor tyrosine kinases:
1. Ligands bind to receptors, cause conformation change, and dimerization of 2 receptors
2. RTK activated by dimers and phosphorylates tyrosines on receptor dimer from ATP
3. Docking sites for downstream signaling molecules activated
How many ATP are necessary for RTK phosphorylation?
6 - or as many as OH groups
