Lecture 11 - SNAREs 2: Membrane fusion machinery in health & disease

Question 1

What do SNAREs drive?

Answer 1

SNAREs drive membrane fusion

Question 2

What happens when the SNAREs end on sister complexes?

Answer 2

Taken apart via NSF and ATP hydrolysis

Question 3

What processes occur to drive membrane fusion?

Answer 3

• nucleation
• zippering
• fusion-pore opening
• addition of NSF and SNAPs
• ATP hydrolysis
• budding

Question 4

What happens when you inhibit membrane fusion?

Answer 4

The warming of flies leads to paralysis, however if you cool them back down, they are normal again. This is because the recycling of SNAREs after membrane fusion is allowed and the proteins becomes functional again in the permissive temperature.

Question 5

What phenotype is seen with a mutation in the VAMP2 gene in mice?

Answer 5

die at birth, loss of synaptic transmission

Question 6

What phenotype is seen with a mutation in the Syntaxin1A gene in mice?

Answer 6

No gross abnormalities. Subtle defects in synaptic transmission

Question 7

What phenotype is seen with a mutation in the Synataxin1B gene in mice?

Answer 7

Die after birth. Reduced synaptic transmission

Question 8

What phenotype is seen with a mutation in the SNAP25 gene in mice?

Answer 8

Die at birth. Loss of synaptic transmission

Question 9

What disease arises from a mutation in VAMP in humans?

Answer 9

Neurodevelopmental disorder with hypotonia (reduced muscle tone) and autistic features with or without hyperkinetic movements

Question 10

What disease arises from a mutation in SNAP25b in humans?

Answer 10

Neurodevelopmental disorder with seizures, intellectual disability, severe speech delay, and cerebellar ataxia (problems with movement)

Question 11

What disease arises from a mutation in SNAP29 in humans?

Answer 11

Cerebral dysgenesis, neuropathy, ichthyosis, and CEDNIK syndrome (palmoplantar keratoderma syndrome)

Question 12

What disease arises from a mutation in Syntaxin11 in humans?

Answer 12

Familial haemophagocytic lymphohistiocytisis (type4)

Question 13

What type of mutation in VAMp2 causes a serious neurodevelopmental disorder?

Answer 13

Heterozygous mutations

Question 14

What is the effect of S75P mutation?

Answer 14

slows the rate of liposome fusion

Question 15

What is familial haemophagocytic lymphohistiocytosis?

Answer 15

• rare disease of the immune system
• predominantly effects infants
• over proliferation of T cells, natural killer cells, B cells & microphages
• life threatening condition (cytokine storm)
• caused by mutation in several different genes
• patients can die from infection die to defective killing in T-cells

T-cells kill infected cells by secreting cytotoxic granules

Question 16

What does a mutation in syntaxin11 causes?

Answer 16

FHL4
- STX11 is a Q-SNARE that doesn’t have a transmembrane domain
- Patients with FHL4 have significantly reduced levels of STX11
- Loss of STX causes defective degranulation from cytotoxic T-cells by an unclear mechanism

Question 17

What does a mutation in Munc18-2 cause?

Answer 17

Munc18-2 causes FHL5 and reduces the levels of STX11

Question 18

What are clostridial neurotoxins?

Answer 18

Clostridial neurotoxins are a group of potent toxins produced by bacteria of the Clostridium genus. These toxins primarily affect the nervous system, leading to various types of neurological disorders.

The most well-known clostridial neurotoxins are produced by Clostridium botulinum and Clostridium tetani, which cause botulism and tetanus.

Question 19

Describe the global trend of global tetanus deaths

Answer 19

Decrease from 300,000 (1990) to 50,000 (2017)
- mainly in under 5

Question 20

What is the most common form of botulism?

Answer 20

Babies <6 months most susceptible - floppy baby syndrome

Question 21

What are toxins dependent on?

Answer 21

Toxins are zinc dependent proteases

Question 22

Are clostridial toxins taken up by all neurons?

Answer 22

They are only taken up neurons

Question 23

Do clostridial neurotoxins cleave the same SNAREs?

Answer 23

no - different SNAREs

Question 24

What is the difference between Tetanus & Botulinum toxins?

Answer 24

They have a similar mode of action but intoxicate different neurons

Question 25

Describe Botulinum neurotoxins and their clinical uses

Answer 25

• Cosmetic uses
• Strabismus, blepharospasm, hemifacial spasm, cervical dystonia, axillary hyperhidrosis, over active bladder, GI tract disorders, sialorrhea, temporomandibular disorder and limb spasticity
• most products are based around Botulinum A and target SNAP25
• Treatment last for several months
• can’t make medicines based around tetanus as everybody is vaccinated against the toxin.

Due to their high efficacy, tolerance, longevity and satisfactory safety profile, BoNTs are now the most widely used therapeutic proteins

Question 26

What is the Botulinum market currently valued at?

Answer 26

nearly 5 billion dollars

Question 27

What can Botulinum A be used to treat?

Answer 27

Strabismus (cross-eyes)

Question 28

What can Botulinum B be used to treat?

Answer 28

cervical dystonia

Question 29

Summarise SNAREs 2

Answer 29

• disruption of SNARE function causes severe defects in neurotransmission and other physiological processes that require membrane fusion
• inherited SNARE based diseases are relatively rare
• botulinum and tetanus toxins have a conserved protein structure
• botulinum and tetanus toxins are potent inhibitors of SNARE function
• botulinum toxins can be used to treat neurological conditions associated with neuronal hyperactivity