Lecture 17 - Signal Transduction Receptors and G Proteins Flashcards
How many genes codre for a G protein coupled receptor in the genome?
Give examples of ligands that bind to receptors involved in G protein signal transduction
True or False: 7 subunit transmembrane G protein receptor has sequence diversity for recognizing different G proteins for binding
over 1000 genes
1) Ca+2
2) Odorants, Pheremones
3) small mols = AAs, amines, nucleotides/(sides), prostaglandins, PAF, peptides
4) Proteins = TSH, LH, FSH, interleukins, chemokines
True
Describe the pathway for G protein signal transductions
Which side of the membrane is the amino terminus and carboxyl terminus?
1) Ligand binds to extracellular receptor
2) conformation change in receptor
3) receptor seeks out G protein and interacts with it
4) G protein is activated
5) G protein binds to effector enzyme and activataes it
6) causes change in [] of 2nd messengers
extracellular side is amino terminus; cytoplasmic side is carboxyl terminus
1) True or False: the G Protein is monomeric
2) What are the subunits of the G Protein?
3) Which subunit shows diversity?
4) Which subunit does GTP bind to?
5) Which subunit binds to the effector mol?
6) True or False: There’s a unique protein/effector mol for each receptor
1) False, the G Protein molecule is heterotrimeric, it has 3 subunits
2) alpha, beta and gamma
3) apha subunit
4) alpha subunit
5) alpha subunit
6) False
Name the diversity within the alpha subunit and which pathways it effects in the cell.
1) alpha i = ion channels, inhibition of cAMP, activation of phospholipases and phosphodiesterases
2) alpha s = increase cAMP
3) alpha q = activate phospholipase C –> degrades phosphotidylinositol –> diacylglycerol and inositol triphosphate
4) alpha I2 = rho GEFs
Describe the steps of the G Protein cycle
1) GDP is attached to inactive G Protein (inactive alpha subunit)
2) receptor interacts with G Protein = promotes conformational change and nucleotide exchange
3) GDP is released and a new GTP binds
4) G protein and alpha subunit is activated and beta and gamma subunits are released
5) G protein does work
6) eventually, alpha subunit (enzyme) performs GTP hydrolysis –> P leaves GTP and G protein is left with GDP on alpha subunit
7) beta and gamma subunits join and G Protein inactivates
What happens if G Protein finishes its cycle and hormone is still bound to the receptor?
G protein will go around the cycle again
Give an example of a protein/enzyme that G Protein activates
what does this activated enzyme do?
What does the 2nd messenger do?
How does this last activation occur?
adenylate cyclase
produce ubiquitous 2nd messenger, cAMP
activates Protein Kinase A (cAMP-dependent protein kinase)
1) increased cAMP activates kinase by binding to R subunits of R2C2 protein complex
2) Rs dissociates from the Cs
3) Free catalytic C subunits go and phosphorylate a limited number of substrate proteins on specific serine or threonine residues
How does adenylate cyclase produce cAMP?
What is cAMP often turned into?
produces cAMP with ATP
AMP –> no longer can degrade cAMP
What does a phosphodiesterase do in relation to cAMP?
What does a phosphoprotein phosphatase do in relation to cAMP?
converts cAMP –> AMP. This removes the intracellular 2nd messenger signal for protein kinase A activation
removes (dephosphorylates) the phosphates from proteins that protein kinase A phosphorylated
What does is the MCIR receptor?
What is the typical pathway involving this receptor?
What do mutations lead to and whats the pathway?
What happens with Agouti?
G protein linked receptor which activates adenylate cyclase
alpha - MSH binds to MCIR receptor –> g protein…… protein kinase activated –> produces eumelanin –> black pigment –> horse is black
red/yellow pigment; mutation in MCIR –> stops normal pathway –> goes to default color (produces pheomelanin)
restricts black pigment synthesis –> stops alpha-MSH hormone from bindign –> bay horse with black marks
What happens in G-Protein Coupled receptors?
same process on both sides –> one adenyl cyclase effector mol –> 2 sets of receptor, hormone and G protein
one side has a stimulatory G Protein –> inc cAMP production
other side has an inhibitory G Protein –> dec cAMP production
How can cAMP regulate gene expression?
1) cAMP activates PKA
2) PKA translocates into nucleus
3) PKA phosphorylates CREB
4) CREB binds with CREB-binding protein to promotor (txn factor)
5) inc txn of protein
How can hormone receptor interactions regulate gene expression?
1) hormone binds to enzyme-linked receptor
2) activates catalytic domain
3) autophosphorylates
4) phosphorylates SMAD regulatory protein
5) activated SMAD dissociates from receptor, binds to a different SMAD and translocates to nucleus
6) binds to promotor region as txn factor where other gene regulatory proteins bind –> inc txn
What is cGMP signal transduction?
guanylate cyclase makes cGMP (for vascular smooth muscle)
cGMP dependent protein kinase (PKG) is activated by cGMP
causes dilation of vessels; increaes in blood flow
cGMP phosphodiesterase removes cGMP (prohibits blood flow)
What does Viagra do?
it is an inhibitor of cGMP phosphodiesterase –> prolongs increased blood flow
Name the three ways receptor signaling can end
Which two aren’t permanent?
1) Receptor inactivation - something binds to base of receptor –> alters structure of receptor so even if hormone is bound, it can’t continue signaling cascade –> desensitized receptor
2) Receptor internalization - recycle parts of membrane with receptors –> remove them –> are isolated in endosome (vessicle) –> can come back to surface and participate again
3) Receptor down-regulation - membrane is isolated in endosome and then fuses with a lysosome and is degraded
receptor inactivation and internalization
