GPCR

Question 1

Improperly folded proteins have the following effects (5)

Answer 1

Aggregation-prone
Bind chaperones
Non-functional (improper interactions or non-productive interactions)
Targeted to degradation
Resource Drain : energy and material

Question 2

What is the ER signal sequence?

Answer 2

Protein sequence on the N-terminal that allows ER import

Question 3

How does the GPCR have so many loops inside the membrane?

Answer 3

multiple stop and start sequences

Question 4

General role of molecular chaperones

Answer 4

Assist proteins during their maturation

Question 5

What do the molecular chaperones bind to on the protein so assure proper maturation?

Answer 5

Hydrophobic segments that could potentially bind to these same segments on other proteins

Question 6

If hydrophobic segments from different proteins bind, what does this cause?

Answer 6

aggregation

Question 7

3 functions of chaperones

Answer 7

General folding helpers
Formation of disulfide bridges
Enzymes of the quality control cycle

Question 8

Example of a chaperone that helps folding, what does it do?

Answer 8

BiP : prevents premature and incorrect folding of segments that arrive in ER lumen

Question 9

Example of chaperone that helps the formation of disulfide bridges

Answer 9

Protein Disulfide Isomerase (PDI)

Question 10

Two enzymes of the quality control cycle? what do they do?

Answer 10

Calnexin (membrane)
Calreticulin (soluble)

They bind to glucosylated oligosaccharides of incompletely folded proteins and prevent aggregation until PDI arrives

Question 11

What is glycosylation?

Answer 11

Addition of oligosaccharides

Question 12

The addition of oligosaccharides (glycosylation) serves as what?
The presence of sugars is used to monitor the _____ state of a protein

Answer 12

a tag to mark the state of protein folding

folded

Question 13

What enzyme does glycosylation?

Answer 13

Oligosaccharyl transferase

Question 14

Quality control cycle:

What happens after addition of sugars? This leaves what as a substrate? What chaperone acts on that substrate?

Answer 14

Trimming in the ER (removal of 2-3 outer chain glucose)
Leaves one glucose
Calnexin acts on glucose

Question 15

Quality control cycle:

After action of calnexin on the single glucose substrate, which enzyme comes into play and what is their role?

Answer 15

Glucosidase

Removes remaining glucose and allows the protein to continue folding

Question 16

Quality control cycle:

What happens if the protein is incompletely folded after already going through a quality control cycle?

Answer 16

A single terminal glucose is readded by glucosyl transferase and a calnexin is regenerated. This is repeated until protein is properly folded.

Question 17

4 modifications to create a functional receptor

Answer 17

Glycosylation
Palmitoylation
Disulfide bridges
Dimerization

Question 18

Which chaperone is important for dimerization of GPCR?

Answer 18

Dimer-probing chaperone

Question 19

Where does dimerization of GPCR happen?

Answer 19

Membrane of ER

Question 20

What happens to unfolded and monomeric GPCRs?

Answer 20

Degraded by ER-associated degradation pathway

Question 21

After GPCR dimerization at ER, GPCRs are matured in the ____

Answer 21

Golgi

Question 22

After maturation of GPCR at Golgi, GPCR homodimers go to the ____________ where they interact with ______

Answer 22

plasma membrane

heterotrimeric G protein

Question 23

5 GPCR dimerization functions

Answer 23

Ontogeny
Ligand-promoted regulation
Pharmacological diversity
Signal transduction
Internalization

Question 24

3 ER retention motifs?

Answer 24

KDEL
KKXX
RXR

Question 25

which proteins have KDEL motif?

Answer 25

ER luminal chaperone proteins (BiP + PDI)

Question 26

with proteins have KKXX motif?

Answer 26

type I integral membrane proteins

Question 27

Role of KDEL and KKXX motifs?

Answer 27

Recycling proteins from Golgi back to ER

Question 28

RXR motif found where?

Answer 28

several GPCRs

Question 29

Role of RXR motif?

Answer 29

Precludes exit of proteins from the ER

Question 30

Two proteins involved in trafficking

Answer 30

SNARE proteins | Rab GTPases

Question 31

Role of SNAREs?

Answer 31

Recognition and catalyze fusion of transport vesicles with target membrane

Question 32

Role of Rab GTPases?

Answer 32

Regulate docking and tethering of the transport vesicle to the target membrane.

Question 33

Rabs in GDP-bound state are ____ and at ______

Answer 33

inactive | cytosol

Question 34

Rabs in GTP-bound state are _____ and at _____

Answer 34

active | membrane of an organelle or transport vesicle

Question 35

True or False | Each different Rab protein controls a different transport pathway between the ER and plasma membrane

Answer 35

True, different proteins control different pathways

Question 36

True or False : | Each Rab protein has a specific SNARE protein that will target them

Answer 36

True

Question 37

GPCRs can ______ or bind to ______

Answer 37

dimerize | G protein

Question 38

GPCR's final destination is the ________

Answer 38

plasma membrane

Question 39

3 steps in signal transduction regulation

Answer 39

Desensitization Sequestration Recycling/Downregulation

Question 40

What is desensitization and why does it happen?

Answer 40

Removal of receptor so it cannot accept more hormone/signal

Question 41

What happens in the desensitization step of signal transduction regulation?

Answer 41

Phosphorylation of receptor by GRK2 Arrestin recruitment Clathrin recruitment and coats plasma membrane Dynamin surrounds neck of vesicle and pinches it off

Question 42

Sequestration : two classes of GPCRs?

Answer 42

Class A | Class B

Question 43

Sequestration : what does the Class A GPCR do?

Answer 43

Removal of arrestin and hormone so the receptor can be reused

Question 44

Sequestration : what does the Class B GPCR do?

Answer 44

Slow recycling? | Degradation

Question 45

Recycling/Downregulation : what is the mechanism?

Answer 45

Dephosphorylation of receptor by PP2A | Removal from it's ligand

Question 46

True or False : | Receptor localization is static

Answer 46

False

Question 47

The vesicle that gets pinched off to eventually get recycled is called the ________

Answer 47

early endosome

Question 48

Clathrin-coated pits internalization: | What are to components involved in the coat nucleation and assembly?

Answer 48

``` AP-2 AP180 Clathrin Synaptotagmin PIP2 Cargo ```

Question 49

Clathrin-coated pits internalization: | What are the components involved in the coated pit maturation?

Answer 49

Dynamin Endophilin Amphiphysin Actin

Question 50

Clathrin-coated pits internalization: | What are the components involved in Fission of the vesicle?

Answer 50

Dynamin | Endophilin

Question 51

Clathrin-coated pits internalization: | What are the componentsa involved in uncoating?

Answer 51

Hsc70 Auxilin Synaptojanin Stoned B

Question 52

Do early endosomes have lower or higher pH and why?

Answer 52

Lower so it can release the receptor and ligand

Question 53

What are the markers in the early endosome?

Answer 53

EEA-1 proteins | rab5-GDP

Question 54

Role of recycling endosomes?

Answer 54

Return the receptor to the cell surface by binding to the plasma membrane

Question 55

Marker for recycling endosome?

Answer 55

Rab4-GDP

Question 56

Late endosomes : low or high pH

Answer 56

Low

Question 57

Markers for late endosomes

Answer 57

rab7-GDP LBPA MPR+

Question 58

Can late endosomes digest all materials? If not, what do they do? What is the marker for this?

Answer 58

No Fusion to lysosome LAMPs

Question 59

Enzymes in the lysosome

Answer 59

``` Acid hydrolases Lipases Carbohydrases Proteases Nucleases Phosphoric acid monoesters ```

Question 60

Markers for the lysosome

Answer 60

LAMP+ Acid hydrolases MPR negative

Question 61

Why would a receptor have to be degraded rather than recycled? (3)

Answer 61

If it requires cleavage during activation If it is bound to irreversible ligands Proteins that are not recycled back to plasma membrane, coming from the endocytic pathway

Question 62

If there is accumulation of proteins in the cytosol, what does this affect?

Answer 62

Transport to ER

Question 63

If there is accumulation of protein in the rough ER, what does this affect?

Answer 63

Budding of vesicles from rough ER

Question 64

If there is accumulation of protein in the ER-to-Golgi transport vesicles, what does this affect?

Answer 64

Fusion of transport vesicles with Golgi

Question 65

If there is accumulation of protein in the Golgi, what does this affect?

Answer 65

Transport from Golgi to secretory vesicles

Question 66

If there is accumulation of protein in the secretory vesicles, what does this affect?

Answer 66

Transport from the secretory vesicles to the cell surface

Question 67

What are the two fates of misfolded proteins?

Answer 67

Ubiquitination and degradation by proteasome Molecular chaperones remodel the protein

Question 68

Which diseases cause misfolding? (4)

Answer 68

CF Marfan Syndrome Nephrogenic Diabetes Insipidus Alpha-1-Antitrypsin Deficiency

Question 69

Which diseases cause retention in the ER?

Answer 69

CF Nephrogenic Diabetes Insipidus Alpha-1-Antitrypsin Deficiency

Question 70

Which disease cause aggregation in the brain after protein release?

Answer 70

Creutzfeldt-Jakob Disease | Alzheimer's

Question 71

Phamacological chaperones role?

Answer 71

Stabilize protein conformation so it can redirected to the plasma membrane rather then to the proteasome/lysosome for degradation

Question 72

Lack of proper folding results in what? (3)

Answer 72

Aggregation Intracellular retention of proteins that shouldn't be there Destruction of proteins that should be expressed

Question 73

Mistrafficking provokes ______ and ______ of essential proteins

Answer 73

Intracellular retention | Degradation