Membrane Fusion

Question 1

What are the 3 types of SNARE proteins?

Answer 1

1. Syntaxins
2. SNAP-25
3. VAMP

Question 2

What unique physical characteristic does SNAP 25 have that Syntaxins and VAMP do not?

Answer 2

They get palmitylated (or modified with a fatty acid).

The palmityl FA then anchors the protein in the membrane.

Question 3

What is the H-domain (or SNARE domain)?

Answer 3

It is a amphipathic alpha helix domain that can form coiled coils.

Question 4

What is responsible for “unwinding” SNARE complexes? How many ATPs are required to unwind?

Answer 4

• NSF (Hexomeric ATPase) and
• Alpha-SNAP(acts as an adapter for NSF)

6 ATPs

Question 5

What does n-sec1 do?

Answer 5

After NSF unwinds the SNARE complex, the proteins are basically denatured and non-functional. nsec1 has activator and inhibitor functions

Activator- need n-SEC1 to fold syntaxin into an active form.

Inhibitor-Binds syntaxin and prevents binding. Its like a trigger.

Question 6

How does viral membrane fusion work?

Answer 6

They form a coiled coil which brings the 2 membranes together (this is how they overcome repulsion). Specificity comes from conformational changes of viral proteins when interacting with certain cells/conditions

Question 7

How many alpha helices form a SNARE?

Answer 7

4 parallel alpha helices.

Question 8

What is the difference in viral binding between HIV and Influenza?

Answer 8

HIV is receptor binding dependent (CD4 receptor).

Flu is pH dependent.

Question 9

Where do most HIV entry inhibitors bind?

Answer 9

Pocket binding site. It is currently too difficult to get binding specificity to amphipathic alpha helices.