GPCR Lifecycle and Pharm Chaperones

Question 1

Improperly folded proteins are…

Answer 1

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

Question 2

Signal hypothesis

Answer 2

N-terminal sequence is an ER signal sequence and directs ER import of the protein containing it
The protein has to be integrated into the membrane before the rest of the protein can be synthesized
Also can be a cleavage signal to cause a protein to stay in the ER

Question 3

Functions of molecular chaperones

Answer 3

Assist proteins during their maturation
Help with folding
Cover interaction domains while they are being synthe sized
Promote folding to allow proper disulphide bonds to form
Act as enzymes for the quality control cycle

Question 4

Why glycosylation?

Answer 4

Addition of oligosaccharides in the ER serves as a tag to mark the state of protein folding

Question 5

3 modifications needed to make a GPCR

Answer 5

Glycosylation
Palmitoylation
Disulphide bridges

Question 6

5 GPCR dimerization functions (in general, what is possible with dimers)

Answer 6

Ontogeny
Ligand-promoted regulation
Pharmacological diversity
Signal transduction
Internalization

Question 7

SNARE proteins

Answer 7

Facilitate recognition and catalyze fusion of transport vesicles with the target membrane
At least 20 different ones
Each is associated with a specific membrane-encolsed organelle involved in the secretory or endocytic pathway

Question 8

Rab GTPases

Answer 8

Rabs regulate docking and tethering of the transport vesicle to the target membrane
Rabs facilitate matching of v-SNAREs with t-SNAREs

Question 9

Early endosomes

Answer 9

Have lowered pH which can release the receptor and ligand

Can be recycled from here

Question 10

Late endosomes

Answer 10

Formed as the pH continues to drop
Degrade many proteins and lipids but may not be able to digest all the material
Can sometimes be recycled from here

Question 11

Lysosomes

Answer 11

End product of endocytosis

Once here, cannot be recycled - only getting chopped up into parts

Question 12

Degradation

where does it occur, and what does it occur to

Answer 12

In lysosome
Occurs for receptors that require cleavage during activation
And for receptors bound to irreversible ligands that were not removed by low pH
Also for proteins that are not recycled back to plasma membrane

Question 13

Cystic fibrosis

1. Protein affected
2. Molecular defect

Answer 13

1. Cystic fibrosis transmembrane regulator

2. Misfolding and retention in the ER, leading to degradation

Question 14

Pharmacological chaperones

Answer 14

Bind to misfolded proteins and stabilize them in the right conformation so that molecular chaperones can come and fix them completely