Lecture 13 - Protein trafficking in epithelia 2 (TBC)

Question 1

How can Genetic polymorphisms or mutations alter protein trafficking pathways?

Answer 1

Genetic polymorphisms or mutations alter protein trafficking pathways to reduce or increase cell surface populations disrupting ion transport pathways

Question 2

What difference in epithelial protein trafficking causes cystic fibrosis?

Answer 2

Very little DF508-CFTR reaching the apical membrane

Question 3

How is protein trafficking in epithelia affected by Liddle’s syndrome?

Answer 3

In Liddle’s syndrome ENaC endocytosis is inhibited causing severe hypertension.

Question 4

What signal does proteins destined for the ‘secretory pathway’ (e.g. ER/Golgi/cell surface/lysosomes) contain?

Answer 4

a hydrophobic signal sequence, located at the N-terminus or further into a protein.

Question 5

Where do ENaC, CFTR and Na+/K+-ATPase have internal signal sequences?

Answer 5

In their transmembrane domains

Question 6

What amino acid sequence do ER localised proteins contain for protein trafficking signalling?

Answer 6

ER localised proteins contain the amino acid sequence: KDEL (K=lysine, D=aspartic acid, E=glutamic acid, L=leucine).

Question 7

What sets up topology (orientation) of membrane proteins?

Answer 7

Hydrophobic and positive stretches of amino acids set up topology (orientation) of membrane proteins

Question 8

Which is the correct order for entry of secretory pathway proteins into the endoplasmic reticulum (ER)?
A. Signal peptide cleaved -> protein enters via translocon -> binding of ribosome to ER
B. Protein enters via translocon -> signal peptide cleaved –> SRP (signal recognition particle) binds signal sequence
C. SRP binds signal sequence -> ribosome docks on ER -> protein enters via translocon

Answer 8

B. Protein enters via translocon -> signal peptide cleaved –> SRP (signal recognition particle) binds signal sequence

Question 9

What does glycosylation in post translational modifications in the ER aid?

Answer 9

Aids protein folding

Question 10

What can glycosylphosphatidylinositol (GPI) anchors replace?

Answer 10

GPI anchors may replace transmembrane domains

Question 11

Where are GPI anchors usually found?

Answer 11

On apical proteins

Question 12

What are the steps of folding and assembly in post-translational modifications occuring in the ER?

Answer 12

1.Disulfide bridges/bonds formed in α, β and γENaC subunits.
2. Correct folding mediated by molecular chaperone proteins.
3.Assembly of subunits into multiprotein complexes.

Question 13

What is the ER quality control system?

Answer 13

ER recognises whether proteins are ‘ready’ to move onto the Golgi, need to stay in the ER longer, or whether they need to be destroyed.

Question 14

What is ERAD?

Answer 14

ERAD is a Endoplasmic Reticulum Associated Degradation protein responsible for the recognition and clearance of terminally misfolded proteins in the ER

Question 15

What is the role of chaperones in the ER Quality Control System?

Answer 15

Chaperones determine if a protein is incorrectly folded or misassembled. These proteins are sent for degradation (ERAD).

Question 16

What does the most common mutation causing cystic fibrosis (DF508-CFTR) prevent?

Answer 16

CFTR reaching the apical membrane. DF508-CFTR protein can’t be folded into the correct structure so gets stuck in the ER and does not move to golgi.
- instead is tagged by the ubiquitin pathway

Question 17

Assertion question:
Misfolded proteins are targeted for degradation in the lysosome
BECAUSE ERAD determines whether proteins are ’ready’ to move further through the secretory pathway

Answer 17

E – Both false
Proteasome not lysosome
Chaperones not ERAD

Question 18

How do ENaC, CFTR and Na+/K+ ATPase complexes
move to plasma membrane?

Answer 18

The constitutive pathway

Question 19

What occurs during Post translational processing in the Golgi?

Answer 19

1. Modification of sugars/N-linked glycosylation occurs sequentially through the Golgi stacks.
2. Addition of sugars to serine/threonines of proteins =
   O-linked glycosylation.
3. Sulfation of sugars and some tyrosines.