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BIOC2003 > Protein trafficking > Flashcards

Protein trafficking Flashcards

1
Q

2 ways to transport from 1 membrane compartment to another

A
  1. Vesicular transport
    - budding, movement through cytoskeletal -> fusion
  2. Direct fusion
    - hybrid organelle
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2
Q

The function of coats for transport vesicles:

A
  1. structural - form and deform

2. selective of which proteins come in and out

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3
Q

How are clathrin vesicles formed?

A
  • Ligand binds to receptor
  • receptor recognised by adaptor
  • clathrin + adaptor recruit at plamsa membrane + start to bud
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4
Q

What type of structure is formed by clathrin and adaptors?

A

Big lattice like structure

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5
Q

Elaborate on the process of budding

A

Neck is pinched by GTPase -> vesicle -> as soon as coat forms its disassembled by Hsp70
-> clathrin and adaptors forms another vesicle

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6
Q

What are the functions of the two different SNARE proteins?

A

t-SNARE : fusion from target membrane

v-SNARE: fusion from vesicle membrane

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7
Q

Mechanism of fusion in endocytosis

A
  1. Uncoated - V-snare exposed
  2. Targeting recruits Rab proteins
  3. Rab binds to effector
  4. V-snare provides 1 alpha helix + t-SNARE provides 3 helixes
  5. 4 helical bundles fuse -> membrane fuses
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8
Q

Trans-snare pairing

A

Interaction across 2 membranes

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9
Q

Cis-snare pairing

A

if same membrane

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10
Q

Homotypic/ heterotypic fusion

A

fusing same or different things

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11
Q

v-SNARE and t-SNARE for exocytosis

A

vAMP and syntaxin

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12
Q

Mechanism of vesicle docking

A
  1. Rab GTP on vesicle binds to effector
  2. Assembly of snare complex -> V +T + Snap 25
  3. Membrane fusion
  4. cis-SNARE complex contacts a-SNAP on NSF protein
  5. SNARE complex disassembles using ATP
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13
Q

How are some ER proteins resident?

A

When a cop II vesicle buds, it selects proteins it needs but takes some liquid from compartment which contains soluble ER protein.
ER proteins have a KDEL sequence at C-terminal
-> enters golgi 1st compartment (cis-golgi)
-> pH in cis-golgi lower so KDEL receptor binds to protein
-> KDEL receptors part of COP1 protein coat
COP1 transfers vesicles from cis-golgi to ER

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14
Q

How do TM ER proteins stay resident?

A

When in cis-golgi lys-lys-x-x (KKXX) retrieval signal causes TM protein to be part of COP1 membrane

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15
Q

Secretion/ exocytosis from ER

A

A means of protein sorting

  1. Cop II transport vesicle from cis- medial to trans goglgi
  2. From trans either constitutitive secretion by vesicles to plasma membrane
  3. or regulated secretion into secretory vesicles by signal
    e. g. insulin
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16
Q

As proteins move through golgi stack they’re modified, modifications include:

A
  • early : phosphorylation of oligo sach. on lysosomal proteins
  • cis-cist. -> removal of c. sugars
  • medial -> +/-
17
Q

After core glycosylation of a protein….

A

Trimming within the ER into golgi -> further adds proteins + sugars -> complex oligosach

18
Q

Why is Endo H- sensitivity important?

A

Allows us to see at what point along the golgi a protein has reached. There’s a specific point X where proteins become endo-H resistant by golgi man II

19
Q

O-linked glycosylation

A
  • addition of sugars to OH serine/ theoirine by glycosyl transferase enzymes
20
Q

How do proteins get from 1 golgi to another?

A
  1. Small vesicles bud off and fuse -> next -> balanced by backwards transport => net forward
  2. transport via cisternal maturation model
    - > compartment will mature to next type of golgi balanced by vesticular transport through transport to protein compartment
    - > acquires enzymes from next compartment while sending its own enzymes backwards
21
Q

Lysosome

A

Degrades proteins + lipids

  • > fuses with late endosome and reformed
  • acidic pH
22
Q

How proteins recruited get to lysosome?

A
  1. Mannose + lysosomal hydrolase precursor from ER in cis-golgi
  2. P-GlcNAc added to complex
  3. complex travels through golgi
  4. M6P signal uncovered at medial-golgi
  5. Binding to M6P receptor at trans golgi
  6. Clathrin coat forms and vesicle fuses with late endosome
  7. ATP hydrolysis energy used to remove P-GlcNAc
  8. Phosphate removed
  9. Late endosome becomes lysosome
23
Q

If mannose 6-phosphate can’t be added…

A

lysosome hydroxylase secreted

  • > mucolipidsis type II
  • > non-functioning lysosome
24
Q

Yeast screens

A

involved mutagenizing yeast and assaying for secretion of a vacuolar protease

25
Q

Endocytosis of LDL receptor

A
  1. LDL is taken to plasma membrane and binds to LDL receptor
  2. The cytosolic end of the receptor has a endocytosis signal and a coated pit
  3. Vesicle forms + uncoats
  4. Fuses with endosome by signal : FDNPVY
  5. Early endosome becomes late endosome when receptor dissociates
  6. Receptor is transported back to plasma membrane by recycling endosome
26
Q

How does the adaptor recognise the endocytosis signal?

A

Conformational change when ligand binds

27
Q

How was the LDL receptor endocytosis signal discovered?

A

•Joseph Goldstein and Michael Brown were studying
patients with familial hypercholesterolaemia
•One patient had an amino acid change -NPVY- to
-NPVC- in the cytoplasmic domain of the LDL receptor
•LDL still binds the mutant receptor but fails to internalise
•LDL can not be cleared from the blood

28
Q

Endocytosis of EGF

A
  1. EGF binds to receptor at plasma membrane
  2. FYRAL signal trigger ubiquitination
  3. Ubiquitin recognised by escort proteins
  4. Signal to inner membrane of late endosome (multi vesicular body)
  5. Fuses into lysosome
29
Q

Implications of endocytosis of EGF

A
  1. Can’t signal - removes cytosolic protein

2. Fused with lysosome - degraded

30
Q

Transfection methods to study protein trafficking

A
  1. Tag with GFP

2. Transfect into cell

31
Q

Problem with protein trafficking studies

A

Pathways are saturable

-> overexpression -> wrong place

32
Q

Example of viruses exploiting protein trafficking

A

e. g. Influenza
- > endocytosis
- > binds to cellular receptors on csm
- > endosome -> acidification of enosomes
- > HA fusion peptie fuses with endsome membrane due to conformational change

BIOC2003 (13 decks)

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