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MCB2050 > Unit 4: ER to Golgi > Flashcards

Unit 4: ER to Golgi Flashcards

1
Q

ERES

A

ER exit sites

  • distinct subdomain of the ER
  • located next to cis face of Golgi complex
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2
Q

ERES is enriched with molecular machinery responsible for ____

A
  • formation of budding of membrane bound vesicles destined for Golgi
  • proper packaging of vesicles with the correct lumenal and membrane cargo proteins destined for Golgi
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3
Q

Do resident ER proteins enter the Golgi destined transport vesicles?

A
  • prevented from entering Golgi-destined transport
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4
Q

What are the three major classes of coat proteins?

A
  1. COPII (anterograde) ER to Golgi
  2. COPI (retrograde) Golgi to ER
  3. Clathrin (from Golgi or PM to endosomes)
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5
Q

Where do COPII-coated vesicle assemble?

A

ERES

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6
Q

Transport Vesicle Assembly at the ERES:

Step One

A
  • soluble COPII component Sar1-GDP (Sar1 = Gprotein) recruited from cytosolic surface of the ERES
  • Sar1-GDP binds a guanine-exchange factor, which generates Sar1-GTP
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7
Q

What is GEF?

A

Guanine Exchange factor

- ER integral membrane protein that catalyzes the exhange of GDP for GTP on Sar1

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8
Q

Transport Vesicle Assembly at the ERES:

Step Two

A
  • Sar-1-GTP integrates into the ER outer leaflet at ERES

- Results in membrane curvature of the ERES membrane

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9
Q

Transport Vesicle Assembly at the ERES:

Step Three

A
  • Sar1-GTP recruits other soluble COPII components
  • from cytosol to surface of ERES membrane
  • Sec23 and Sec24
    …
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10
Q

Transport Vesicle Assembly at the ERES:
Step Three
What happens to Sec 23 and Sec 24

A
  • form a dimer to promote further bending ERES membrane
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11
Q

Transport Vesicle Assembly at the ERES:
Step Three
What does Sec24 do?

A
  • Sec24 also binds to cytosolic-facing domains of selected integral membrane including
  • membrane cargo proteins
  • membrane cargo receptors proteins
  • membrane receptor proteins required for trafficking and docking
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12
Q

Transport Vesicle Assembly at the ERES:

Step Four

A
  • additional soluble COPII components recruited to cytosol to surface of growing coated vesicle ‘bud’
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13
Q

Transport Vesicle Assembly at the ERES:
Step Five
What happens after COPII coat assembly?

A
  • vesicle bud pinches off from ERES and vesicle begins to traffic to proper recipient membrane
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14
Q

Transport Vesicle Assembly at the ERES:
Step Five
What happen prior to vesicle fusion with the Golgi?

A
  • COPII coat disassemble
  • SarI-GTP is converted back to Sar1- GDP
  • and released along with all of the other COPII proteins
  • into the cytosol for another round of COPII coat assembly at ERES
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15
Q

What is a Rab protein?

A
  • large family of lipid-anchored membrane proteins
  • located on all transport vesicles and recipient membranes
  • vesicle targeting specificity and unique rabs to different membranes
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16
Q

What does the association of the Rab protein with a membrane require?

A

GTP

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17
Q

Vesicle targeting and fusion at CGN

Step 1

A

Recognition of the incoming vesicle and recipient membranes

18
Q

Vesicle targeting and fusion at CGN

Step 2

A

Tethering of the incoming vesicle to recipient membrane

19
Q

What do GTP-Rabs do?

A
  • complementary membrane bound
  • recruit various recipient factors
  • act like tethering proteins
  • from cytosol to surface of the vesicle and recipient membranes
20
Q

What are tethering proteins?

A
  • highly elongated (fiber-like, rod-shaped)proteins

- or components of large multi-protein complexes

21
Q

What do tethering proteins do?

A
  • form a molecular bridge

- mediate vesicle membrane-recipient membrane contact by bringing the two membranes close together

22
Q

What is step 3 of vesicle targetting and fusion at CGN?

A

docking of the vesicle at recipient membranes

23
Q

What mediates the 3rd step of vesicle targetting?

A
  • SNARE proteins help docking
24
Q

What are SNARE proteins?

A
  • large family of integral membrane-bound proteins located on all transport vesicles AND all recipient membranes
  • specificity (unique vesicle targeting)
25
Q

What is a SNARE motif?

A
  • all SNARE proteins have a SNARE motif
  • cytosolic facing domain that extends from membrane surface
  • SNARE-SNARE protein binding
26
Q

2 main classes of SNARE proteins

A

v snares

t snares

27
Q

Explain v-SNARES

A
  • vesicle membranes
  • incorporated into vesicle membrane at site of budding on donor comparment
  • i.e. at ERES vSNARE incorporated into golgi-destined VESICLE MEMBRANE
28
Q

What are t-SNARES

A
  • target acceptor membranes

- i.e. at the cis Golgi

29
Q

What is the SNARE complex? What mediates it?

A

v-snare + t=SNARE

- cytosolic facing SNARE motif mediates

30
Q

What is step four of vesicle targeting fusion at CGN?

A

fusion of vesicle and acceptor membranes

31
Q

What does the SNARE complex do? (4th step of vesicle targeting and fusion)

A
  • pulls opposing vesicle and recipient membranes together = fusion
32
Q

What does the vesicle-recipient membrane fusion result in?

A
  1. Lateral movement of vesicle membrane proteins (cargo and receptors) into recipient membrane
  2. Release of vesicle soluble ‘cargo’ proteins into the interior lumen of the acceptor organelle
33
Q

What is the fate of vesicle specific proteins or proteins that escape from the ER?

A

returned from the CGN to the ER by specific ER retrieval signals via retrograde transport

34
Q

What is the direction of retrograde transport?

A

cis-Golgi to ER

35
Q

What sequence do most resident soluble ER proteins possess?

A

KDEL sequence

36
Q

What are examples of ER retrieval signals?

A 
KDEL sequence
KKxx sequence (cytosolic facing)
37
Q

What is the role of the KDEL sequence?

A

recognized in the CGN by KDEL receptor

38
Q

What does the KDEL sequence bind to?

A
  • lumenal side - binds KDEL sequence of escaped protein in CGN lumen
  • cytosolic side- binds COPI components
  • releases once reaches ER
39
Q

What is the role of COPI?

A
  • mediates the formation of transport vesicles at the CGN

- return soluble ER protein KDEL receptor complex back to ER

40
Q

What is the role of the KKxx sequence?

A
  • cytosolic facing
  • sequence on escaped ER membrane proteins at the CGN
  • recognized by COP1
  • COP1 coated vesicles return resident ER to ER
41
Q

What else has a KKxx ER retrieval signal?

A

KDEL receptor

MCB2050 (10 decks)

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