lecture 3 Flashcards
how many molecules do GPCR ligands encompass/recognize
huge variety
examples of ligands GPCRs recognize
peptides, steroid hormones, smell, sight, etc.
how many times does GPCR pass thru membrane
7 times
describe inactive receptor
not bound to anything; no kinase, no enzymatic characteristics
describe heterotrimeric G proteins
not bound to receptor, hanging out in the vicinity b/c bound to each other
what has lipid anchors
2 members of heterotrimeric complex; so anchored to plasma membrane
why are they anchored to memrbane
close proximity to receptor
what happens when GPCR is activated
signaling molecule binds it
what does molecule binding to receptor cause
conformational change in G receptor allowing it to bind to heterotrimeric complex
what specific part of heterotrimeric complex does G receptor bind to
G alpha
what does activation of G alpha cause
heterotrimeric G protein to dissociate (it’s active now)
what happens to G protein
dissociates, moves along plane of plasma membrane to activate downstream proteins
what is brown blob
adenylyl cyclase (enzyme, now activated)
what do trimeric G proteins do
relay signals from GPCRs
where are trimeric G proteins associated
w/ inner leaflet of plasma membrane
describe inactive form of heterotrimeric G complex
only G alpha is bound to GDP
what does G alpha bound to GDP repesent
inactive form; GDP means off
where is G alpha anchored
plasma membrane
where is G gamma anchored
plasma membrane
where is beta
helps hold alpha and gamma together in off form
what happens when GPCR is activated
it acts like a GEF and triggers activation of its associated G protein
what happens when signaling molecule arrives
conformational change in GPCR
example of conformational change
loop on cytoplasmic face unfolds; activation dependent conformational change
what does activation dependent conformational change allow
allows it to bind and activate G alpha
what is that activation
GPCR is gonna act as a guanine exchange factor
what is above mechanism
mechanism of activation of G alpha
what does GEF do
kicks off GDP, replaces it with GTP
what happens to alpha when activated
G alpha dissociates from beta gamma, floats freely
what happens to beta and gamma
remain stuck together; they are also activated
what happens to GPCR
remains activated; if any other copies of inactive form of heterotrimeric G protein complex its gonna bind and activate them until ligand is gone / pathway desensitized
where is the signaling happening at this step of pathway
at plasma membrane (b/c GPCR is in plasma membrane)
what does phosphorylated mean
activated
what do lipid anchors do
hold proteins at certain locations
what do some G proteins do
regulate production of cyclic AMP
what happens after G alpha becomes activated by exchanging GDP for GTP
it activates adenylyl cyclase
what does adenylyl cyclase do
converts ATP into a cyclized version called cyclic AMP
KNOW
adenylyl cyclase is responsible for converting ATP to cAMP
what does cAMP act as
second messenger; binds and activates downstream proteins to propagate signal further into cell
is cAMP a protein or chemical
chemical
how do we get rid of cAMP
phosphodiesterase; converts cyclic AMP to AMP
why does converting cAMP to AMP work
AMP is nolonger capable of signaling
what does adenylyl cyclase do
converts ATP to cAMP
what does cAMP do
allows signal propagation
what does phosphodiesterase do
destroys cAMP & turns off pathway
what mediates most of the effects of cyclic AMP
cyclic AMP dependent protein kinase (PKA)
describe cAMP molecule
small, water soluble; good at diffusing thru cytoplasm but can’t cross lipid bilayers
what part of step is at lipid membrane
GPCR (transmembrane protein), G alpha and beta-gamma (cuz of lipid anchor) adenylyl cyclase
how does adenylyl cyclase meet G alpha
they’re all stuck at plasma membrane so that’s where they meet
where does cAMP go
free to diffuse into cytoplasm [departure point from membrane]
what is cAMP’s target
protein kinase A / PKA
describe inactive PKA
cytoplasmic protein (not associated w/ membranes)
describe structure of PKA
tetramer: 2 regulatory subunits, 2 catalytic subunits
what do PKA regulatory subunits do
when bound to catalytic subunits, they regulate them and hold them off –> PKA off
describe PKA off
2 regulatory subunits bound to catalytic subunit
what does cAMP do when diffuses through cytoplasm
binds to catalytic subunit
how many molecules of cAMP needed to activate 2 copies of PKA
4 molecules of cAMP to activate 2 copies of PKA
describe this signaling step
reduction instead of amplification
give examples of amplification in steps
one GPCR activates several g alpha proteins which activate several adenylyl cyclases, create hundreds of thousands of copies of cAMP [each step gets more and mroe abundant]
what happens when cAMP binds to regulatory subunit
activates pKA, releases it from regulatory subunits
what does activated PKA do
phosphorylates downstream targets in nucleus
what do Gs proteins do
generation of cyclic AMP and PKA activation
describe transport in and out of nucleus
highly regulated, activation dependent
what does activation of PKA do for nucleus
represents mechanism to get signaling across nuclear pore and into nucleus & change gene transcription
where does PKA go when activated
enters nucleus thru nuclear pore
what is end goal of PKA
change gene transcription
how many copies of PKA enter nucleus
2 copies
what does PKA do when in nucleus
phosphorylates creb protein
what does phosphorylation of CREB do
when activated CREB initiates transcription of target gene
what is output of PKA pathway
change in gene regulation
how does PKA changing gene regulation happen
g alpha activates adenylyl cyclase, converts ATP to cAMP, activates PKA, enters in nucleus, phosphorylates CREB and activates it which activates target gene transcription
what was the Gs subunit dependent on
adenylyl cyclase
name another GPCR pathway
some G proteins signal via phospholipids
what happens when GPCR becomes activated
G alpha protein is activated
what does activated G alpha do
binds and activates phospholipase c-B
what does phospholipase c-B do
cleaves PI 4,5-bisphosphate into diacylglycerol and IP3 (inositol 1,4,5-trisphosphate)
where does diacylglycerol remain
embedded in plasma membrane
describe structure of diacylglycerol
head group is polar and water soluble
where does IP3 go
into endoplasmic reticulum
what G protein is for adenylyl cyclase pathway
G alpha S
what G protein is for phospholipase pathway
G alpha q
how do we distinguish these two pathways
by the specific G protein being activated
why is calcium kept in ER and out of cytoplasm
very potent second messenger; kinda like cAMP would just bind and activate shit
describe structure of IP3
polar head group of PIP2
what happens once IP3 when cleaved
nothing holds it to plasma membrane so it diffuses to cytoplasm
what does IP3 see in cytoplasm
ion gated receptor activated by ligand binding in ER membrane
what happens when IP3 binds channel
its a calcium channel, so when IP3 binds it floods calcium from ER into cytoplasm & triggers signaling
what does IP3 do w/ DAG
cooperates w/ diacylglycerol to activate protein kinase C, further downstream steps
what do all GPCRs activate
Galpha subunits to trigger downstream signaling
what can GPCRs do to target gene transcriptoin
activate cAMP production
what can GPCRs do for calcium
open IP3 gated channels in ER to trigger calcium signaling
