Membrane Fusion

Question 1

Is membrane fusion thermodynamically favorable or unfavorable?

Answer 1

Unfavorable - highly inefficient

- need machinery!

Question 2

Name 2 molecular motor proteins and where they direct vesicles

Answer 2

dynein - to golgi
kinesin - away from golgi

helps deliver vesicle to fusion site via actin/tubule tract

Question 3

What proteins aid membrane fusion?

Answer 3

SNARE (soluble NSF attachment protein receptor)

Question 4

3 classes of SNARE proteins and where they are located

Answer 4

1. syntaxin
   
   • target membrane
2. (VAMPS) - vesicle associated membrane protein
   
   • transport vesicle
3. (SNAPS) - synaptosome associated protein
   
   • target membrane

all 3 associate (coiled coil) during membrane fusion

Question 5

structure of:
1. syntaxin
2. VAMPS
3. SNAPS
(recall figure from lecture)

Answer 5

1. 3 amphipatic helices, huge helical domain, transmembrane domain
2. 2 huge helical domains sandwiched by CCCC
3. huge helical domain, transmembrane domain

Question 6

Describe the disassembly of SNARE complex

Answer 6

after fusion, cell needs to recycle SNARE proteins for more fusion events

NSF binds to complex, uses 6 ATP hydrolysis to disassemble 1 SNARE complex (unwinds coiled coil)

Question 7

Sec1 protein function

Answer 7

after disassembly of SNARE complex, proteins needs to be unwound and changed into active conformation

Question 8

Viral mediated membrane fusion steps

Answer 8

enveloped virus uses membrane fusion to infect cells

1. prefusion
2. extended intermediate
3. collapse of intermediate
4. hemifusion
5. fusionpore (post fusion)

Question 9

structure of viral fusion proteins

Answer 9

1 transmembrane domain (inserted into viral membrane)

1 hydrophobic fusion domain (hidden in viral protein)
- inserted into target cell membrane and collapses with signal and fusion

Question 10

What causes viral fusion of influenza?

Answer 10

Drop in pH = viral envelop fuse