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Biochemistry Pulmonology > ER/Golgi transport > Flashcards

ER/Golgi transport Flashcards

1
Q

Golgi order

A
  1. Cis-network
  2. Cis
  3. Medial
  4. Trans
  5. Trans-network (TGN)
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2
Q

Possible destination from the Trans-Golgi-Network (TGN)

A

—> late endosome —> lysosome

—> constitutive secretion

—> regulated secretion

(Retrograde) to trans-Golgi and beyond

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3
Q

As the golgi cisternae move to their new location…the mature through ?

A

Retrograde movement of enzymes needed for an earlier compartment

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4
Q

Anterograde movement =

Retrograde movement =

A
  1. Cisternal maturation

2. Retrograde vesicles

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5
Q

Three different types of vesicles

A
  1. COPII (anterograde)
  2. COPI (retrograde)
  3. Clathrin/adapter protein (TGN —> endosome/lysosome & plasma membrane —> endosome)
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6
Q

GTPase for COPII vesicles

A

Sar1

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7
Q

GTPase for COPI vesicles

A

ARF

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8
Q

GTPase for all non-COPII vesicles

A

ARF

= COPI + all clathrin vesicles

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9
Q

Trans-golgi —> endosome

Adapter protein?

A

Clathrin + AP1 complexes (or GGA)

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10
Q

Plasma membrane —> endosome

Adapter proteins?

A

Clathrin + AP2 complexes

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11
Q

Golgi —> lysosome, melanosome, or platelet vesicles

Adapter proteins?

A

AP3 complexes

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12
Q

How are integral proteins carried in COPII vesicles from ER —> cis-Golgi

Soluble proteins?

A

Integral = inserted in the vesicle membrane

Soluble = bind to specific ER membrane-bound receptors

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13
Q

What does the COPII coat protein bind to?

A

The cytosolic domains of the integral membrane cargo

The receptor for the soluble cargo

The cytosolic domains of the ER membrane…curved nature gives the vesicle a round shape

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14
Q

What happens once the formation of COPII vesicle is complete and pinches off the ER?

A

The vesicle starts to de-coat (lose the COPII proteins)

Exposes the v-SNAREs proteins in the vesicle membrane

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15
Q

Role of the v-SNAREs

ER —> cis-golgi

A

Bind to t-SNAREs (target SNAREs)

Mediating vesicle fusion

At this point…

The integral cargo is now integral to the cis-membrane

The soluble cargo is bound to its receptor, bound to the cis-membrane

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16
Q

COPI transport

A

Same mechanism as COPII

Just in reverse direction and different coat protein

Still uses v and t-SNAREs

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17
Q

GTPase function in vesicle transport

A
  • binds GTP and hydrolyzes the GTP —> GDP

COPI = ARF

COPII = Sar1

Two important functions

  1. Vesicle formation
  2. De-coating
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18
Q

GTP-bound form of GTPase (Sar1 or ARF)

A

N-tail of protein extends into the vesicle membrane (hydrophobic interactions)

Can interact with coat proteins (COPI/II)

Therefore…Sar1 or ARF aids in

  1. The binding of the coat proteins
  2. Recruitment of cargo (indirectly)
  3. Inherent curvature of vesicle
19
Q

GTP hydrolysis by GTPase

A

Promotes conformational change of GTPase

Retracts N-tail out of membrane

Lessens the coat proteins association with the vesicle membrane

Mediates coat dissassmebly

20
Q

Processing of N-linked oligosaccharide complex

Cis golgi vs. trans golgi

A

Cis = high mannose glycosylation

Trans = complex glycosylation

**proteins can be hybrids of both

21
Q

High mannose modifications can be enable proteins to be targeted by ?

A

Lysosomes

22
Q

High mannose gylcosylation

A

(Man)8(GlcNAc)2 —> (Man)5(GlcNAc)2

**lose 3 mannose

23
Q

In TGN,

To get proper cargo into the correct type of transport vesicle…

A

The adapter protein (AP) binds a cytosolic domain sorting signal on the cargo (or cargo receptors)

The AP also interactes with the coat protein (usually Clathrin)

24
Q

What transport from the TGN would not have clathrin as the coat protein?

A

Retrograde from the TGN —> trans-golgi

COPI

25
Q

Cargo signal for TGN —> lysosome transport

A

Mannose-6-phosphate (M6P)

26
Q

I-Cell Disease

General/symptoms

A

General theme: mis-targeting of proteins from the TGN

Symptoms: 1yr old coarse facial features, craniofacial abnormalities, psychomotor retardadtion, stunted growth

27
Q

M6P modification sorting signal

TGN —> lysosome transport

A

Occurs on one of the mannose sugars on the N-linked oligosaccharyl high mannose complex

28
Q

TGN —> lysosome transport

Steps

A
  1. M6P lysosomal proteins packaged into AP3 containing vesicles (M6P receptor)
  2. De-coats

2A. Clathrin and AP3 are recycled back

  1. Uncoated vesicle fuses with late endosome/lysosome
  2. Low pH in lysosome, acid hydrolase (M6P protein) now active

4A. M6P receptor is recycled back to TGN

  1. Or to the plasma membrane…in case a hydrolase is accidently released out of cell
29
Q

Mechanism of I-cell Disease

A

Lysosomal proteins are not tagged with M6P

Therefore…all of lysosomal proteins are do not go to lysosomes…but instead are constitutively secreted out of the cell

Now lysosomes cannot break down substrates

30
Q

How the M6P cargo signal is created in the cis-golgi

A

UDP-GlcNAc (substrate) used to add GluNAc-phosphate to one of the mannose sugars

Enzyme #1 = GlcNAc phosphotransferase

Then GlcNAc is removed to leave the M6P sorting signal

Enzyme #2 = phosphodiesterase

31
Q

What enzyme is blocked by I-Cell Disease

A

GlcNAc phosphotransferase

Prevents any M6P from being made

Causes a build up of multiple types of inclusion bodies within the lysosome (mainly carbs and lipids)

32
Q

what is I-cell disease referred to as ?

A

Mucolipidosis (ML-II)

Characteristics of mucopolysaccharidoses and sphingolipidoses (both types of LSDs)

33
Q

ML-I

A

Sialidase deficiency

34
Q

ML-III

A

Pseudo-Hurler Polydystrophy

Less severe case of I-cell disease (same enzyme)

35
Q

What is the root cause of most LSD? And why are ML-II/III different

A

Single defective hydrolase…so get a buildup of a single class of molecule

ML-II/III have a problem in the targeting part of a lysosomal formation…so many types of molecules build up

36
Q

MPS-I

A

Name = Hurler-Scheie syndrome

Enzyme = alpha-L iduronidase

37
Q

MPS-II

A

Hunter syndrome

Iduronate-2-sulphatase

38
Q

MPS-III

A

Sanfilippo syndrome

Heparan-N-sulphatase

Alpha-N-acetlyglucoaminidase

AcetlyCoA:N-acetyltransferase

N-acetylglucosamine 6 sulphatase

39
Q

Gaucher disease

A

Beta-glucosidase

40
Q

Gangliosidosis type I

A

Tay Sachs disease

Beta-hexosaminidase A

41
Q

Gangliosidosis type II

A

Sandhoff disease

Beta-hexoaminidase A and B

42
Q

Lysosome pH range

A

5.0-6.0

43
Q

Cytosolic pH

A

7.2-7.4

44
Q

Endocytosis

A

Plasma membrane invaginates to form small endocytic vesicles (endosomes)

Biochemistry Pulmonology (12 decks)

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