Through and out of the golgi

Question 1

What are the 2 models for movement of proteins through and out of the golgi?

Answer 1

• Cisternal maturation
• Vesicle Transport

Question 2

What is the cisternal maturation model of protein movement through the golgi?

Answer 2

• Golgi cisternae mature as they migrate through the stack and cargo moves with them
• The cargo is then sorted and budded off at TGN
• Golgi enzymes are transported back by COPI vesicles

Question 3

Why is it important that golgi enzymes are returned back by COPI vesicles?

Answer 3

To maintain important compartment identity and function

Question 4

What is the vesicle transport model of protein movement through the golgi?

Answer 4

• Golgi cisternae are static components and the enzymes are maintained in specific compartments
• Cargo move forward in vesicles

Question 5

How are proteins modified with mannose-6-phosphate sorted by the TGN?

Answer 5

• Collected in clathrin coated vesicles and diverted via endosomes to lysosomes

Question 6

Give an example of a protein with a mannose-6-phosphate that is sorted by TGN

Answer 6

Acid-hydrolase responsible for lysosomal degradation

Question 7

What occurs in the default pathway of the TGN?

Answer 7

• Delivers material to the plasma membrane in a non-specialised manner
• Likely involves accumulation of cargo in specific regions of TGN

Question 8

How are proteins with specialised secretory signals sorted by TGN?

Answer 8

Packaged into vesicles for regulated secretion

Question 9

Where are acid hydrolases modified with an M6P tag?

Answer 9

In the golgi

Question 10

How are acid hydrolases at TGN selected?

Answer 10

• Lumenal domain of M6P receptor binds to M6P tag
• Cytosolic domain sorting signals are recognised by clathrin adaptor complexes

Question 11

How are acid hydrolases at TGN moved into lysosomes?

Answer 11

• Clathrin adaptor complexes recruit clathrin coat to package receptors and hydrolase cargo into vesicles and deliver it into early endosomal system
• Trafficked onto lysosomes

Question 12

How is the M6P tag removed from acid hydrolases?

Answer 12

As early endosomes mature, the pH changes and drops which causes a dissociation of M6P from the receptor

Question 13

How is the clathrin coat assembled?

Answer 13

• receptor and lumenal protein encodes particular sorting motifs and are recognised by adaptor proteins
• Adaptor complexes come together and collect up cargo receptors and clathrin assembles in triskelion to generate membrane curvature
• Proteins involved in membrane bending pinch off vesicle

Question 14

Where on clathrin serves as a binding site for many adaptor proteins?

Answer 14

Globular domain

Question 15

What does adaptor sorting motif recognition co-operate with for co-incidence detection?

Answer 15

Binding of membrane phospholipids

Question 16

How is AP2 released from locked conformation?

Answer 16

• Binds to PIP2
• Triggers a conformational rearrangement that makes sorting motif binding sites accessible

Question 17

How can AP2 selectively function at the plasma membrane?

Answer 17

• in order to intract with sortng motifs to initiate coat formation it must be activated by binding to PIP2 which is found at the plasma membrane

Question 18

What does the AP1 complex recongise at the golgi in order to allow it to function at a specific site?

Answer 18

PI(4)P

Question 19

What is the function of dynamin?

Answer 19

‘pinches off’ clathrin coated vesicles

Question 20

What is the structure of dyamin?

Answer 20

• Large modular GTPase
• Self-assembles into tubular polymers which undergo a conformational change to promote scission

Question 21

Where are clathrin adaptor complexes employed?

Answer 21

The late secretory and endocytic pathways