SNARE Proteins Mediate Fusion Between Vesicles and Target Membranes

Question 1

What is required once a vesicle is formed? for what purpose?

Answer 1

additional proteins are needed to ensure delivery of the vesicle to the appropriate destination

Question 2

What does sorting and targeting of vesicles involve?

what are they? (2) what do they do?

Answer 2

• two families of SNARE (SNAP receptor) proteins
• v and t SNAREs are complimentary molecules that allow recognition between vesicles and their targets
• v-SNAREs (vesicle-SNAP receptors) on vesicles
• t-SNAREs (target-SNAP receptors) on target membranes

Question 3

what happens when a vesicle reaches its destination?

Answer 3

a third family of proteins, Rab GTPases (specific for different destinatins), come into play

Question 4

What do Rab GTPases do?

what does this do?

Answer 4

• lock the complementary SNARE proteins together

- this facilitates membrane fusion

Question 5

what happens following vesicle formation?

Answer 5

N-ethylmaleimide sensitive factor (NSF) and a group of soluble NSF attachment proteins (SNARES) mediate release of the SNARESof the donor and target molecules

Question 6

what does recent research suggest?

what else is there?

Answer 6

SNAREs are not solely responsible for targetting specificity.
-tethering proteins

Question 7

what do tethering proteins do?

Answer 7

act over longer distances and appear to provide specificity by connecting vesicles to their target membranes prior to v-SNARE/t-SNARE interaction

Question 8

what are the main groups of tethering proteins? (2)

Answer 8

1. coiled coil proteins such as golgins

2. multisubunit complexes such as exocyst complex

Question 9

what are coiled coil proteins, such as golgins, important for?

Answer 9

important in recognition and binding of COPI and COPII vesicles to the golgi

Question 10

what are multisubunit protein complexes, such as exocyst complext important for?

Answer 10

important for protein secretion

Question 11

chemical blocking of SNARE complex formation does not…

Answer 11

abolish vesicle-target interaction: all as implicates as initial recognition and specificity of vesicle-target interaction

Question 12

what are some other type of multisubunit protein complexes? (3)

Answer 12

1. COG (conserved oligiomeric golgi) complex
2. GARP (golgi-associated retrograde protein)
3. TRAPP (transport protein particle)