Surface Receptors Flashcards
four main types of surface receptors based on structure/function
- 7 transmembrane domain
- growth factor receptors
- cytokine receptors
- guanylyl cyclase receptors
(5.) novel cell surface receptor
GPCR N terminus
extracellular domain
- recognizes and binds to ligand, causes conformational change
GPCR C terminus
intracellular domain
- c terminus; hydrophilic; transduce signal via G proteins (interacts w G protein timer, always in cytosol)
what are the 7 hydrophobic segments that span the membrane of GPCR’s also called
serpentine receptors
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
pindolol
is a nonselective beta blocker
- receptor antagonist
iodocyanopindolol
is a b1 adrenoreceptor antagonist and a serotonin receptor antagonist
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
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
Specific Disease of G Protein
Specific Disease of G Protein
Signalling: Cholera toxin
(bacterium Vibrio cholerae) blocks
GTPase activity of alpha subunit
and so cAMP stimulation constant
__ 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
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..
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 …..
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…..
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)
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
