Protein trafficking 3

Question 1

Import to ER sequence signal

Answer 1

6-12 hydrophobic amino acids

-> always on end of C terminus

Question 2

Translation for ER imports

Answer 2

Co-translational

Question 3

Mech of ER import

Answer 3

ss on mRNA binds to soluble receptor protein which binds to receptor

• > receptor is a translocin
• > SRP and SRPR receptor displaced when at translocin
• > GTP hydrolysis required for assembly of nascent chain/ translocin complex + release of SRP

Question 4

SRP characteristics

Answer 4

6 proteins and 1 sRNA

Question 5

How is SRP transferred to Sec61 translocin

Answer 5

Ribosome with ss binds to SRP and transfers to sec61

Question 6

Outline co-translational translocation

Answer 6

1. only across 1 membrane -> after translocation, protein is kept unfolded by Hsp70 until it reaches sex 62,63,71/71 receptor complex
2. Through sex61
3. BIP binds to protein lumen uses ATP

Question 7

How to make a ER multi-spanning membrane protein?

Answer 7

1. Ribosome and protein in active transolocator
2. Signal sequence cleaved
3. Releases protein into ER lumen
4. Stop and start (hydrophobic regions) -> want to stay in membrane
5. Reaches another hydrophobic region that spans membrane by # time region allows
   => multi-spanning because it’s built up as translation occurs

Question 8

ER is the site of

Answer 8

Glycolysation

Question 9

Glycolysation helps with X and Y

Answer 9

X - folding

Y - stability

Question 10

Process of glycolysation

Answer 10

Sugar attaches to aspargine in protein by oligosaccharyl transferase
N-X-S / N-X-T

Question 11

ER also site of

Answer 11

Disulphide bridges ( S-S)

Question 12

Outline ERAD

Answer 12

ER associated degradation

• chaperones assist incorrectly folded proteins by polyubiquitination -> degraded by proteosome
• < transported by dislocation out of cytosol by chaperone

Question 13

A co-translational import requires

Answer 13

GTP

Question 14

A post-translational import required

Answer 14

ATP

Question 15

3 ways to study protein trafficking

Answer 15

1. Translocation approach
2. Biochemical approach
3. Genetic approach

Question 16

Outline translocation approach

Answer 16

GFP -> indicates entry -> coincides with known ER protein

Question 17

Outline genetic approach

Answer 17

Yeast as amodel organism

-> screens e.g. sec61

Question 18

For every forward transport step, theres a

Answer 18

backward transport step - balances

Question 19

General mechanism of translocation between compartments

Answer 19

1. vesicle from donor compartment -> target

2. “coat” -< electron dense material copI and copII structural and select

Question 20

COPII

Answer 20

ER - cis golgi

• has an associated GTPase
• made up of sec 23,24.13,31,16

Question 21

COPI

Answer 21

Takes vesicles from golgi to ER

-> through golgi cisternae