Surface Receptors

Question 1

four main types of surface receptors based on structure/function

Answer 1

1. 7 transmembrane domain
2. growth factor receptors
3. cytokine receptors
4. guanylyl cyclase receptors
   (5.) novel cell surface receptor

Question 2

GPCR N terminus

Answer 2

extracellular domain
- recognizes and binds to ligand, causes conformational change

Question 3

GPCR C terminus

Answer 3

intracellular domain
- c terminus; hydrophilic; transduce signal via G proteins (interacts w G protein timer, always in cytosol)

Question 4

what are the 7 hydrophobic segments that span the membrane of GPCR’s also called

Answer 4

serpentine receptors

Question 5

GPR disease

Answer 5

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

Question 6

pindolol

Answer 6

is a nonselective beta blocker
- receptor antagonist

Question 7

iodocyanopindolol

Answer 7

is a b1 adrenoreceptor antagonist and a serotonin receptor antagonist

Question 8

Gαs-AC Coupled Signaling step 1

Answer 8

1) Epinephrine binds
β-adrenergic
receptor with Gαs

Question 9

Gαs-AC Coupled Signaling step 2

Answer 9

2) AC activated to produce cAMP

Question 10

Gαs-AC Coupled Signaling step 3

Answer 10

3) cAMP binds to inhibitory
subunit of protein kinase A
(PKA) and releases enzyme

Question 11

Gαs-AC Coupled Signaling step 4

Answer 11

4) PKA phosphorylates substrates

Question 12

Gαs-AC Coupled Signaling step 5

Answer 12

5) CREB = cAMP response

Question 13

Specific Disease of G Protein

Answer 13

Specific Disease of G Protein
Signalling: Cholera toxin
(bacterium Vibrio cholerae) blocks
GTPase activity of alpha subunit
and so cAMP stimulation constant

Question 14

__ binds to consensus
___ in basal state, but when
____ is activated
to enhance transcription

Answer 14

CREB binds to consensus
CRE in basal state, but when
phosphorylated is activated
to enhance transcription

Question 15

GTP

Answer 15

= guanosine triphosphate

Question 16

GDP

Answer 16

GDP= guanosine diphosphate + free phosphate
(Pi = inorganic phosphate)

Question 17

G proteins

Answer 17

• 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

Question 18

G protein Signaling General Mechanism step 1

Answer 18

1) Inactive complex
(associated
with receptor in
membrane)

Question 19

G protein Signaling General Mechanism step 2

Answer 19

2) Ligand binds inducing
conformation change in
receptor

Question 20

G protein Signaling General Mechanism step 3

Answer 20

3) Receptor-G protein
complex forms and
GDP dissociates from
alpha subunit

Question 21

G protein Signaling General Mechanism step 4

Answer 21

4) GTP binds (GTP 10x>GDP in cytosol)

Question 22

G protein Signaling General Mechanism step 5

Answer 22

5) Gα-GTP dissociate
from receptor and
beta/gamma subunits

Question 23

G protein Signaling General Mechanism step 6a

Answer 23

6a) Gα-GTP act on effectors
(depends on alpha subtype
e.g. PLC, AC)

Question 24

G protein Signaling General Mechanism step 6b

Answer 24

6b) beta/gamma may

also act on effectors

Question 25

G protein Signaling General Mechanism step 7

Answer 25

7) Intrinsic GTPase of alpha converts GTP to GDP

Question 26

G protein Signaling General Mechanism step 8

Answer 26

8) Subunits reassociate

Question 27

G protein Signaling General Mechanism Regulated by..

Answer 27

a) GPR-associated protein (GAP) helps inactivate Gα-GTP and acts as scaffold for assembly b) Receptor desensitization (βadrenergic receptor kinase and arrestin)

Question 28

αs Stimulatory (esp. AC) effector

Answer 28

adenylyl cyclase ca channels k channels

Question 29

ai Inhibitory effector

Answer 29

adenylyl cyclase ca channels k channels

Question 30

aq Stimulates PLC effector

Answer 30

PLCb Other ligands for GPCR using alpha q – Angiotensin II, Bradykinin, Acetylcholine

Question 31

Phosphatidylinositol (4,5)-bisphosphate

Answer 31

(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).

Question 32

IP3

Answer 32

IP3 = inositol triphosphate (2nd messenger)

Question 33

DAG

Answer 33

DAG = diacylglycerol (2nd messenger)

Question 34

Gq-PLC-coupled Signaling step 1

Answer 34

1) Ligand (e.g. Angiotensin II) binds receptor with Gαq

Question 35

Gq-PLC-coupled Signaling step 2a

Answer 35

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)

Question 36

Gq-PLC-coupled Signaling step 2b

Answer 36

2b) DAG may come directly from phosphatidylcholine cleavage

Question 37

Gq-PLC-coupled Signaling step 3a

Answer 37

3a) calcium activates protein kinases, promotes secretion, causes contraction

Question 38

Gq-PLC-coupled Signaling step 3b

Answer 38

3b) DAG second messenger activates protein kinase C

Question 39

Gq-PLC-coupled Signaling step 4

Answer 39

4) PKC numerous substrates, some of which involve transcription effects in the nucleus

Question 40

Desensitization of the β-adrenergic receptor in G protein Signalling step 1

Answer 40

1) Activation of receptor and AC

Question 41

Desensitization of the β-adrenergic receptor in G protein Signalling step 2

Answer 41

2) Phosphorylation of receptor by β-adrenergic receptor kinase βARK , a GRK (G proteincoupled receptor kinase)

Question 42

Desensitization of the β-adrenergic receptor in G protein Signalling step 3

Answer 42

3) Inactive AC; arrestin binds when Pylated and blocks association with G protein

Question 43

Desensitization of the β-adrenergic receptor in G protein Signalling step 4

Answer 43

4) Phosphatase removes phosphate from receptor, allows G protein association and activation of AC

Question 44

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 …..

Answer 44

ADP-ribosylation of Gαs = inhibits GTPase activity – AC active longer – In gut = increase water and salt secretion

Question 45

pertussis toxin is a protein-based AB5-type exotoxin produced by the bacterium Bordetella pertussis – it also causes…..

Answer 45

ADP-ribosylation of Gαi & Gαo prevents G protein binding HR – inactive GDP-bound G protein

Question 46

Genetic disorders in α subunits – Eg. Pseudohypoparathyroidism type Ia (PHP-Ia)

Answer 46

Target cell resistance to PTH, with ↑ [PTH]

Question 47

In Growth Factor Receptors enzyme tyrosine kinase is part of receptor (2)

Answer 47

1) adds phosphate to substrates that recruit other proteins = signaling complexes 2) adds phosphate to proteins that are also kinases = phosphorylation cascades

Question 48

Growth Factor Receptors - Signaling Complexes Step 1

Answer 48

1) Typically dimers form upon ligand binding (but not shown here)

Question 49

Growth Factor Receptors - Signaling Complexes Step 2

Answer 49

2) Autophosphorylation

Question 50

Growth Factor Receptors - Signaling Complexes Step 3

Answer 50

3) recruitment of accessory proteins (SH2 domains recognize phosphorylated tyrosines; SH3 domains recognize proline rich sequences)

Question 51

Growth Factor Receptors - Signaling Complexes Step 4

Answer 51

4) SH3 proteins also have Tyr phosphorylation

Question 52

Growth Factor Receptors - Signaling Complexes Step 5

Answer 52

5) Very large complexes may form with complicated signalling

Question 53

SH2

Answer 53

– src homology domain (type 2)

Question 54

SH3

Answer 54

sh3 type 3