Surface Receptors Flashcards
Gαs-AC Coupled Signaling
step 1
1) Epinephrine binds
β-adrenergic
receptor with Gαs
Gαs-AC Coupled Signaling
step 2
2) AC activated to produce cAMP
from ATP
Specific Disease of G Protein
Signalling
Specific Disease of G Protein Signalling: Cholera toxin (bacterium Vibrio cholerae) blocks GTPase activity of alpha subunit and so cAMP stimulation constant
Gαs-AC Coupled Signaling
step 3
3) cAMP binds to inhibitory
subunit of protein kinase A
(PKA) and releases enzyme
Gαs-AC Coupled Signaling
step 4
4) PKA phosphorylates
substrates
Gαs-AC Coupled Signaling
step 5
5) CREB = cAMP response
element binding protein
__ binds to consensus
___ in basal state, but when
____ is activated
to enhance transcription
CREB binds to consensus
CRE in basal state, but when
phosphorylated is activated
to enhance transcription
Cell Surface Receptors
4 main types (and one novel) based on structure/function:
1) 7 Transmembrane Domain (7 TMD) – G protein Coupled Receptors
(GPRs) - (adenylyl cyclase (AC) or phospholipase C (PLC))
2) Growth Factor Receptors (tyr kinase domain attached)
3) Cytokine Receptors (tyr kinase separate)
4) Guanylyl Cyclase Receptors (cyclase attached)
5) Novel Cell surface receptors – such as ferroportin
Cell Surface Receptors: 7 Transmembrane Receptor/G Protein
Coupled Receptors
7 hydrophobic segments span
the membrane; also called
“serpentine” receptors
Extracellular domain: N terminus;
recognizes and binds to ligand
Cytoplasmic domain: C terminus;
hydrophilic; transduce signal via
G proteins
GPR DISEASE
Mutations in G protein receptors important
pathology in endocrine disorders; often need
homozygous mutation to have loss of function
since excess receptors; also could have gain of
function, if mutation causes constitutive activation;
a single point mutation may also alter binding
specificity or receptor desensitization
GTP
= guanosine triphosphate
GDP
GDP= guanosine diphosphate + free phosphate (Pi = inorganic phosphate)
G-proteins
• Heterotrimers, subunits = αβγ • G-proteins identified by the α-subunit – αs = stimulation of AC – αi = inhibition of AC – αq/11 = stimulation of PLC • α-subunit has GTPase activity • β/γ act as a dimer
G protein Signaling General Mechanism
step 1
1) Inactive complex
(associated
with receptor in
membrane)
G protein Signaling General Mechanism
step 2
2) Ligand binds inducing
conformation change in
receptor
G protein Signaling General Mechanism
step 3
3) Receptor-G protein
complex forms and
GDP dissociates from
alpha subunit
G protein Signaling General Mechanism
step 4
4) GTP binds (GTP
10x>GDP in cytosol)
G protein Signaling General Mechanism
step 5
5) Gα-GTP dissociate
from receptor and
beta/gamma subunits
G protein Signaling General Mechanism
step 6a
6a) Gα-GTP act on effectors
(depends on alpha subtype
e.g. PLC, AC)
G protein Signaling General Mechanism
step 6b
6b) beta/gamma may
also act on effectors
G protein Signaling General Mechanism
step 7
7) Intrinsic GTPase of alpha
converts GTP to GDP
G protein Signaling General Mechanism
step 8
8) Subunits reassociate
G protein Signaling General Mechanism Regulated by..
Regulated by: a) GPR-associated protein (GAP) helps inactivate Gα-GTP and acts as scaffold for assembly b) Receptor desensitization (βadrenergic receptor kinase and arrestin)
αs
Stimulatory
(esp. AC)
effector
adenylyl cyclase
ca channels
k channels
ai Inhibitory effector
adenylyl cyclase
ca channels
k channels
aq Stimulates PLC effector
PLCb
Other ligands for GPCR using alpha q – Angiotensin II,
Bradykinin, Acetylcholine
Phosphatidylinositol (4,5)-bisphosphate
(PtdIns(4,5)P2 or PIP2
) is a minor
phospholipid component of cell membranes. PtdIns(4,5)P2 is enriched at the plasma
membrane where it is an important substrate for a number of important signalling
proteins. Phospholipase C hydrolyzes the phosphodiester link in PtdIns(4,5)P2
forming inositol 1,4,5-triphosphate (InsP3) and diacylglycerol (DAG).
IP3
IP3 = inositol
triphosphate
(2nd messenger)
DAG
DAG =
diacylglycerol
(2nd messenger)
Gq-PLC-coupled Signaling
step 1
1) Ligand (e.g. Angiotensin II)
binds receptor with Gαq
Gq-PLC-coupled Signaling
step 2a
2a) Phospholipase cleavage: PIP2 to IP3 (2nd messenger) causing release of calcium (2nd messenger) to cytoplasm from the ER and also forms DAG (2nd messenger)
Gq-PLC-coupled Signaling
step 2b
2b) DAG may come
directly from
phosphatidylcholine
cleavage
Gq-PLC-coupled Signaling
step 3a
3a) calcium activates protein
kinases, promotes secretion,
causes contraction
Gq-PLC-coupled Signaling
step 3b
3b) DAG second messenger
activates protein kinase C
Gq-PLC-coupled Signaling
step 4
4) PKC numerous
substrates, some of which
involve transcription effects
in the nucleus
Desensitization of the β-adrenergic receptor in G protein Signalling
step 1
1) Activation of receptor and AC
Desensitization of the β-adrenergic receptor in G protein Signalling
step 2
2) Phosphorylation of receptor by
β-adrenergic receptor kinase
βARK , a GRK (G proteincoupled receptor kinase)
Desensitization of the β-adrenergic receptor in G protein Signalling
step 3
3) Inactive AC; arrestin
binds when Pylated and
blocks association with
G protein
Desensitization of the β-adrenergic receptor in G protein Signalling
step 4
4) Phosphatase removes phosphate
from receptor, allows G protein
association and activation of AC
Cholera toxin – (also known as choleragen and sometimes
abbreviated to CTX, Ctx or CT) is protein complex secreted
by the bacterium Vibrio cholerae. It causes …..
Cholera toxin – (also known as choleragen and sometimes
abbreviated to CTX, Ctx or CT) is protein complex secreted
by the bacterium Vibrio cholerae. It causes ADP-ribosylation
of Gαs = inhibits GTPase activity – AC active longer
– In gut = increase water and salt secretion
Pertussis toxin is a protein-based AB5-type exotoxin
produced by the bacterium Bordetella pertussis – it also
causes…..
Pertussis toxin is a protein-based AB5-type exotoxin
produced by the bacterium Bordetella pertussis – it also
causes ADP-ribosylation of Gαi & Gαo prevents G protein
binding HR – inactive GDP-bound G protein
Genetic disorders in α subunits
– Eg. Pseudohypoparathyroidism type Ia (PHP-Ia)
Target cell resistance to PTH, with ↑ [PTH]
In Growth Factor Receptors enzyme tyrosine kinase is part of receptor (2)
In Growth Factor Receptors enzyme tyrosine kinase is part
of receptor
1) adds phosphate to substrates that recruit other proteins
= signaling complexes
2) adds phosphate to proteins that are also kinases
= phosphorylation cascades
Growth Factor Receptors - Signaling Complexes
Step 1
1) Typically dimers form upon
ligand binding (but not
shown here)
Growth Factor Receptors - Signaling Complexes
Step 2
2) Autophosphorylation
Growth Factor Receptors - Signaling Complexes
Step 3
3) recruitment of accessory proteins (SH2 domains recognize phosphorylated tyrosines; SH3 domains recognize proline rich sequences)
Growth Factor Receptors - Signaling Complexes
Step 4
4) SH3 proteins also have
Tyr phosphorylation
Growth Factor Receptors - Signaling Complexes
Step 5
5) Very large complexes may form
with complicated signalling
SH2
– src homology
domain (type 2)
SH3
SH3 – type 3
Phosphorylation Cascades
e.g., insulin, IGF-1 and epidermal growth factor
GRB2
GRB2 – growth factor
receptor bound protein
SOS
son of sevenless
MEK
mitogen activated
protein kinase
ERK
extracellular
signal-regulated kinase
PI3K
= Phosphoinositide 3-
kinases
PDK
PIP3- dependent kinases
PKB
protein kinase B (AKT)
PI3K/PKB common signalling
pathway plus ___ here
show also ___(PDK)
PI3K/PKB common signalling
pathway plus downstream here
show also phosphodependent
kinases (PDK)
MAPK
MAPK
pathway activated =
mitogen activated
protein kinase
Cytokine Receptors – Tyrosine Kinase Separate
include receptors for cytokines but also same structure (so same family)
for: erythropoietin, colony-stimulating factor, prolactin (PRL), and growth
hormone (GH – not to be confused with Growth Factors and GFR)
2 GH receptors brought together by ___ to signal the recruitment of ___ which is a tyrosine kinase
2 GH receptors brought together by GH to signal the recruitment of JAK2 which is a tyrosine kinase
STAT
= Signal Transducers and Activators of Transcription
SIE, GAS and ISRE are \_\_\_ DNA regulatory elements involved in \_\_\_ control of GH targets ie \_\_\_
SIE, GAS and ISRE are STAT-binding DNA regulatory elements involved in txnal control of GH targets ie IGF-1
JAK2
JAK2 = Janus kinase
Guanylyl Cyclase Receptor: The Fourth of the Main Cell Surface
Receptors
Atrial natriuretic peptide
p.418 Role in
hypertension, because
it’s a powerful vasodilator
Kinase-like domain
regulates catalytic domain
of guanylyl cyclase
When ligand binds, conf.
change removes inhibitory
control of cyclase
Mechanisms by which primary messengers stimulate guanylyl cyclase.
Two major
classes of
guanylyl cyclase
(GC) are known: _____
membranebound and
soluble.
Soluble Guanylyl Cyclase
Cytokines
Cytokines are small secreted proteins which mediate and
regulate immunity, inflammation, and hematopoiesis. They must
be produced de novo in response to an immune stimulus. They generally
act over short distances and short time spans and at very low
concentration.
\_\_\_ and \_\_\_ both activate SOLUBLE guanylyl cyclase (GC) to produce \_\_\_\_ from GTP which in turn activates cGMP-dependent protein kinase (PKG), promoting \_\_\_\_
eNOS and iNOS both activate SOLUBLE guanylyl cyclase (GC) to produce cyclicGMP from GTP which in turn activates cGMP-dependent protein kinase (PKG), promoting vasorelaxation
Hepcidin is a polypeptide hormone that is a ___ regulator of body ___ levels.
Hepcidin is released from the ___ when __ levels are __ and there is
inflammation. Liver Hepcidin release will be inhibited by the need for __ during
____. To control ___ release from the gut, liver and WBCs hepcidin
binds to ____. Hepcidin binding causes ____ degradation. ____
presentation can be controlled in a hepcidin dependent and independent fashion
Hepcidin is a polypeptide hormone that is a negative regulator of body iron levels.
Hepcidin is released from the liver when iron levels are high and there is
inflammation. Liver Hepcidin release will be inhibited by the need for iron during
erythropoiesis. To control iron release from the gut, liver and WBCs hepcidin
binds to ferroportin. Hepcidin binding causes ferroportin degradation. Ferroportin
presentation can be controlled in a hepcidin dependent and independent fashion
