RTK/GPCR Flashcards
what do receptor tyrosine kinases control
the rate of cell proliferation and growth
what do insulin receptors regulate
glucose homeostasis
which ligands for RTKs are dimers
PDGF - platelet derived
NGF - nerve
VEGF - vascular endothelial
which ligands for RTKS are monomers and what do they cause
EGF - epidermal
cause conformational rearrangement of the receptor and dimerization
what is receptor dimerization
when two receptor subunits come close to each other
their intracellular domains (tyrosine resideues) cross phosphorylate each other
What does the SH2 domain recognize
P-Tyr and 3 AAs on the C terminal side
PTB domain recognizes
the N terminal side of P-Tyr
SH3 domain recognizes
proline rich sequences
PH domain recognizes
lipids: PI bi and triphosphates
=phosphatidylinositol bi and tri’s (PI3, 4P2, & PI3,4,5P3
etc)
RAS is a
low molecular weight GTPase
slow GTPase so it’s inefficient
what does GTPase Activating protein do
it’s a protein cofactor known as GAP that binds to RAS
turns RAS-GTP into RAS GDP and Pi by increasing efficiency of GTP hydrolysis
what does GDP/GTP exchange factor (GEF) do
changes bound GDP to RAS into the active form Ras-GTP so that GTP can be disassociated from RAS
what are the hydrophobic anchors of RAS that attach it to the plasma membrane so that it can participate in signal transaction
farnesyl residue
Fatty Acid
what are the domains of GRB2
which is used to bind to active RTK
which domain is used to bind to SOS
SH3-SH2-SH3
SH2 binds it to RTK
SH3 binds to SOS
RAS is a significant protein in what
cancer with 40% of solid tumors containing a mutation in RAS
what does activation of the MAP kinase pathway control
cell proliferation
in the cytosol, ERK controls translation by doing what
phosphorylating and inhibiting TSC2
TSC2 is a protein that binds to TSC 1
what do mutations in TSC1 and TSC2 lead to
lymphangioleiomyomatosis and tuberous sclerosis complex
-benign tumors in brain, heart, kidneys, skin
TSC2 is a
GTPase activating protein for Rheb (Ras homolog enriched in brain)
Rheb/GTP activates ____
mTORC1
mTORC1 increases
cell growth by stimulating protein synthesis at the level of translation
TSC1/2 complex acts as a ____ and converts ___
GAP for Rheb and converts Rheb-GTP to Rheb-GDP inactivating it
how do mutations in TSC1/2 cause tuberous sclerosis complex
the TSC1/2 complex is not phosphorylated and inhibited
so the Rheb-GTP is NOT converted to Rheb-GDP (inactive)
so Rheb is in active form Rheb-GTP which activates mTORC1
which increase rate of protein syntheis –> incr size of cell (cell growth) –> cell division rate is same –> tumor formation
what is tuberous sclerosis complex and what’s it caused by
autosomal-dominant multisystem disordor
casuses formation of benign tumors all over body
underlying genetic cause: mutation in TSC1 or TSC2 gene
–> overactivation of rapamycin complex (mTORC)
how to treat Tuberous sclerosis complex
mTOR inhibition such as monoclonal antibody Everolimus
mTOR is aka ___ which is used in the clinic as ___
rapamycin complex which is used as an antiproliferative drug in treating TSC and certain cancers
ways to terminate MAPK pathway
hint: 4 ways
spontaneous hydrolysis of GTP to GDP –> inactivates Ras
Ras-GAP (turns Ras-GTP to Ras-GDP) –>inactivates Ras
protein phosphatases (dephosphorylate and deactivate every component of the signaling pathway)
internalization of the receptor (decr concentration of activated receptor to plasma membrane inhibits the signaling)
T/F:
under basal conditions, PI3K type 1A is active
FALSE
it’s inactive during basal conditions
what are the regulatory and catalytic subunits needed for PI3K path
Regulatory subunit p85 (bound to SH2 domain on receptor to allow p110 to be active)
catalytic subunit p110 (bound to Ras-GTP)
activation of PI3K increase the concentration of what, where
incr conc of PIP3 in plasma membrane
how are PDK1 and AKT recruited to the membrane
via their PH domains
how to terminate the PI3K path
protein and lipid (PTEN) phosphatases dephosphorylate PIP3 to make PIP2 –> inhibits AKT path
what happens to AKT when under basal conditions
AKT not active
PH domain binds to it’s Kinase domain –> inhibits activity
what is req’d to get complete activation of AKT
unfolding
recruitment to plasma membrane
1 or 2 independent phosphorylation events
where does TORC2 phosphorylate AKT
on it’s hydrophobic tail
what happens when the concentration of PIP3 in the membrane is high
PH domain of AKT binds to PIP3 in plasma membrane
enzyme unfolds
PH doesn’t inhibit kinase anymore
PDK1 can phosphorylate the kinae domain while mTORC2 phosphorylates the hydrophobic tail
what would happen if there was a mutation of either PTEN or SHIP2
they’re used to termination PI3K signaling
so if disfunctional –> hyperactivation of PI3K path –> malignant transformation of cells
in the phospholipase C gamma pathway it hydrolyzes ___ which produces ___
hydrolyzes PIP2 –> inositol triphosphate (IP3) & diacylglycerol (DAG)
what does IP3 bind to and cause
binds to specific receptors in the ER
releases calcium in the cytosol
what does DAG activate
PKC - protein kinase C
how does overexpression of ERB2 (aka HER2) lead to breast cancer
incr in basal HER2 signaling
incr cell proliferation
incr cell growth
breast cancer
what does a mutation in an N terminal truncation of the Erb or Her receptor result in
dimerization and constant activation of the mutant receptor in the absence of the ligand
what are two therapy’s for breast cancer
monoclonal antibodies
specific inhibitors of the kinase domain
what are G-protein coupled receptors
7 transmembrane domain receptors that act as GTP/GDP exchange factors for assc heterotrimeric G proteins
after ligand binding, the GPCR acts as a
GTP/GDP exchange factor
what happens when GTP is bound to G-alpha
G-alpha dissacosiates from Beta-gamma
what is the difference bn isoform alpha-i vs alpha-s
alpha-i inhibits adenylyl cyclases –> reduces cAMP
alpha-s stimulates adenylyl cyclases –> incr cAMP
what is different in PI3K type 1B compared to type 1A
type 1B has regulatory subunit type p101 while 1A had p85
however, they have the same catalytic subunit p110
what is the general structure of GCPRS
N terminus on outside of cell
C terminus on inside
water-soluble molcs bind to extracellular domains
hydrophobic molcs bind to transmembrane region
which loop does the ligand-occupied GPCR interact w the G protein
via the 3rd intracellular loop usually
what happens when a ligand binds to GPCR
it gets rid of GDP and a GTP enters –> dissociation of alpha from beta-gamma
T/F
the GTP bound GPCR is the resting state
falso this si the active state
resting is when it is GDP bound
how is the beta-gamma SUs attached to the plasma membrane
prenyl group at the C terminus of the gamma SU
what anchors the alpha subunit to the mebrane
FA residue at the N terminus
GPCR acts as a ____ and facilitates the exchange of ____ at the alpha subunit
GTP/GDP exchange factor and exchanges GDP for GTP at the alpha
what is needed for the alpha subunit to hydrolyze the GTP molc
regulator of G protein signaling (RGS) which stimulates the GTPase activity and turns GTP to GDP
what are some of the targets of various alpha SUs
adenylyl cyclase guanylyl cyclase phosphodiesterase phospholipase ion channels
what is the target of the beta-gamma complex
PI3K type 1B which has most of the same effects as type 1A
cAMP activity is mediated by
PKA
cAMP binds to which subunits of PKA
regulatory
binding of cAMP to regulatory subunits of PKA causes
their dissociation from the catalytic SU and phosphorylation of the downstream substrates
what are the PKA targets and what do they regulate
phosphorylase kinase and glycogen synthase phosphorylation by PKA –> regulates glucose metabolism
hormone sensitive lipase phosphorylation –> regulate lipolysis
CREB (cAMP response element binding protein) –> regulate transcription
PLC-Beta is activated by what subunit
alpha-q
activation of PLCB causes
hydrolysis of PIP2 into
DAG and IP3
what does Diacyl glycerol do in PLCB
stays on plasma membrane
where it activates PKC
what does inositol triphosphate do in PLCB
cleaved off the membrane migrates to ER opens the Calcium channels in the ER Calc rushes into cytosol calcium conc increases
how to terminate PLCB signaling
Calcium-ATPases pump calcium outside the cell or back inside the ER
what does calcium bind to
calmodulin
what happens upon calmodulin binding to atoms of clacoim
calmodulin changes its conformation and activates the enzyma Calcium/calmodulin-dependent protein kinase
what can Calcium/calmodulin-dependent protein kinase phosphorylate
phosphorylase kinase like PKA
PKA and PKC can phosphorylate …
the third intracellular loop and the C terminus of GPCR which impairs its interaction w the G protein
ligand bound GPCRs can be phosphorylated on the C terminus by
G protein coupled receptor kinases (GRK) which interact with arrestins
what happens when phosphorylated DRKs interact with arrestins
interfere w binding to G proteins
recruit clathrin and promote internalization of GPCRs
unlike PKA and PKC, GRK can only phosphorylate …
agonist occupied receptors i.e. receptors bound to ligands
signaling mechanism involved in cholera
cholera toxin ADP-ribosylates alpha-s in the interstinal epithelium and inhibits it’s GTPase activity –> rise in cAMP –>disregulates ion channels –> efflux of watetr and electrolytes into the gut –>diarrhea
Bacterial ADP-ribosylating exotoxins (bAREs) covalently transfer…
ADP-ribose moiety of NAD+ to target proteins of infected eukaryotes –> yield nicotinamide and free Hydrogen ion
pertussis toxin is anoth example of bacterial toxin with ADP-ribosyltransferase activity. what happens when it ADP-ribosylates alpha-i
ADP-ribosylates alpha-i in lung –>blocks intxn w GPCR –>adenylyl cyclase not inhibited –>incr cAMP –>loss of fluids and electrolytes –>incr mucus secretion –> whooping cough
what do outer regions of rods habe
membranes with rhodopsin bound to the 11-cis retinal
what happens to rods when exposed to light
light coverts it from 1-cis to all-trans retinal –> conformational change in rhodopsin –> GDP to GTP exchange in the alpha SU of transducin (G protein) –> liberated alpha SU –> activates cGMP PDE –> decr in cGMP –> cGMP gated non-selective cation channels cause –> membrane hyperpolarization –> inhibition of synaptic signaling
in cone cells,retinal is attached to different opsins so that …
cis/trans isomerization happens in response to photons with different energy
aka light w diff wavelengths: blue, green, red
olfactory GPCRsare coupled to
specific g protein: Golf
what does Golf activate
adenylyl cyclase –> incr cAMP conc –> opens cAMP gated Na channels –> depolarized –>signal sent to brain
which two tastes are mediated by a family of three GPCRs that heterodimerize in diff combos
umami and sweet
all taste receptors are coupled to
specific G protein gustducin which activates PLC-beta
