Membrane Fusion (Exam 3)

Question 1

A transport vesicle fusion involves many coordinated steps. First it needs to be delivered to the fusion site via help of ____ that move along ______.

Answer 1

molecular motor proteins; actin or microtubule tracks

Question 2

Once A transport vesicle is delivered to the appropriate destination it needs to fuse with the target membrane. That is achieved by a help of a set of cellular proteins known as ____.

Answer 2

SNARE (Soluble NSF Attachment protein receptor)

Question 3

There are three main classes of SNAREs:

Answer 3

1. syntaxins
2. VAMPs (vesicle associated membrane protein)
3. SNAPs (synaptosome associated protein)

Question 4

____ is located in transport vesicle, while ____ and____ are located in target membrane.

Answer 4

VAMP; syntaxin, SNAP

Question 5

_____ is what drives membrane fusion.

Answer 5

The formation of the highly stable SNARE complex

Question 6

Once fusion has occurred, the cell needs to recycle the SNARE proteins. Since SNARE complexes are highly stable, the cell has a set of proteins, namely ____ and ______to disassemble SNARE complex. The NSF hydrolysis ____ (uses/does not use) ATP.

Answer 6

NSF (N-ethyl-maleimide sensitive fusion protein); αSNAP (soluble NSF attachment protein); uses (6 ATP)

Question 7

After disassembly of SNARE complex, the SNARE proteins need to be refolded to the active conformation. That is achieved by the ____ protein, which binds and changes ____ into the active conformation.

Answer 7

Sec1; syntaxin. Sec 1 serves as a regulatory molecule to prevent excessive release of vesicles.

Question 8

Regarding VIRAL MEDIATED MEMBRANE FUSION, the SNARE complex analog encoded by viruses contains two domains; a ______ domain that ________, and a _____ domain that is usually _______. Upon receiving a specific signal (ie change of pH for influenza) the fusion domain is exposed and inserted into the _______, which is followed by the refolding of the fusion protein which brings the membranes together.

Answer 8

transmembrane domain that inserts into the viral membrane; fusion domain that is usually hidden within the viral protein; target cell membrane.

Question 9

How does the Botulism toxin work?

Answer 9

Inactivates synaptic release of neurotransmitter by cleaving the SNARE proteins.

Question 10

Describe the processes by which vesicle fusion occurs. Use VAMP, Syntaxin, SNAP, and the domains each uses to accomplish this task.

Answer 10

VAMPs are found in the membrane of the incoming vesicle. SNAPs and syntaxins are found in the target membrane. The three classes of SNARE proteins vary in structure but have one important commonality: the presence of at least one alpha-helical domain, which forms
coiled-coils. When the alpha-helical domains of the SNARE proteins come into contact, they zipper together and form a highly stable complex of coiled-coils. The zippering of the SNARE proteins bridges the two membranes, allowing for fusion. Because the complex is highly stable, the repulsive forces between the membranes are overcome and water molecules between the membranes are forced out.

Question 11

Drugs against enveloped viruses can target which two processes?

Answer 11

Inhibit fusion

Inhibit activation of viral particles that mediate fusion