Lecture 11 - SNAREs II

Question 1

How do SNAREs drive membrane fusion?

Answer 1

1. SNAREs drive membrane fusion by forming a tight complex between the vesicle (v-SNAREs) and target (t-SNAREs) membranes,
2. They pull them close together and catalyse the fusion of their lipid bilayers.
3. The interaction between v-SNAREs and t-SNAREs brings the membranes into close proximity
4. This leads to the formation of a tightly apposed lipid bilayer.
5. The resulting force generated by the assembly of SNARE complexes brings the two membranes close enough to allow their lipids to mix and fuse.
6. This leads to the release of the vesicular contents into the target compartment.

Question 2

What happens when you inhibit
membrane fusion in animals?

Answer 2

In general, inhibition of membrane fusion can interfere with normal cellular processes that rely on the transfer of materials or signals between different compartments, including neurotransmission, hormone secretion, and immune cell function.

Inhibition of membrane fusion can also impair the formation and maintenance of important cellular structures, such as synaptic connections between neurons or the fusion of sperm and egg during fertilization.

Inhibition of membrane fusion can contribute to the pathogenesis of various diseases, such as viral infections, cancer, and neurodegenerative disorders.

Question 3

WHta hapened to the different knock out mice that were generated ti study SNARE function ?

Answer 3

VAMP2 - Die at birth. Loss of synaotic transmission
Syntaxin1A - No gross abnormalities. Subtle defects in synaptic transmission
Syntaxin1B - Die at birth. Reduced synaptic transmission
SNAP25 - Die at birth. Loss of synaptic transmission

Question 4

What disease is caused by mutation of SNAP25b SNARE ?

Answer 4

Neurodevelopmental disorder with seizures, intellectual disability, severe speech delay, and cerebellar ataxia

Question 5

What disease is caused by mutation of VAMP2 SNARE ?

Answer 5

Neurodevelopmental disorder with hypotonia and autistic features with or without hyperkinetic movement

Question 6

What disease is caused by mutation of SNAP29 SNARE ?

Answer 6

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

Question 7

What disease is caused by mutation of Sytaxin11 SNARE ?

Answer 7

Familial hemophagocytic lymphohistiocytosis type 4 (FHL4)

Question 8

What does heterozygous mutations in VAMP2 cause ?

Answer 8

Heterozygous mutations in VAMP2 can cause a rare form of distal arthrogryposis, which is a genetic disorder characterized by the congenital contractures of the limbs, leading to joint stiffness and restricted mobility. This condition is also known as DA5. The mutations in VAMP2 disrupt the function of the protein, which is required for normal muscle development and movement.

Question 9

What does S75P mutation do to liposome fusion ?

Answer 9

The S75P mutation in the SNARE protein syntaxin-1A reduces the efficiency of liposome fusion by impairing the assembly of SNARE complexes. Specifically, this mutation affects the ability of syntaxin-1A to form a ternary SNARE complex with the SNAREs SNAP-25 and synaptobrevin, thereby hindering the formation of the tight and stable SNARE complex necessary for membrane fusion.

It slows down the rate of liposome fusion. It is a negative mutation

Question 10

What is Familial hemophagocytic lymphohistiocytosis (FHL4)?

Answer 10

A rare disease of the immune system

Predominantly effects infants

Overproliferation of T cells, natural killer cells, B cells and macrophages

Life-threatening condition (cytokine storm)

Caused by a mutation in several different genes

Patients can die from infection due to defective killing in T-cells

Question 11

How do T-cells kill infected cells ?

Answer 11

T-cells can eliminate infected or cancerous cells by releasing of cytotoxic granules containing perforin and granzymes. The perforin creates pores in the target cell membrane, allowing granzymes to enter and activate caspases, leading to apoptosis or programmed cell death.

Question 12

How does a mutation in Syntaxin 11 cause FHL4?

Answer 12

STX11 is an unusual Q-SNARE as it does not have a transmembrane domain

Patients with FHL4 have significantly reduced levels of STX11

Loss of STX11 causes defective degranulation from cytotoxic T-cells by an unclear mechanism

Question 13

How does a mutation in Munc18-2 cause FHL5 and reduceS the levels of STX11?

Answer 13

The mutation in Munc18-2 disrupts its interaction with STX11, which is a key regulator of T-cell cytotoxicity. As a result, the levels of STX11 are reduced, leading to impaired T-cell function and the inability to kill infected cells effectively.

Question 14

What are Clostridial neurotoxins ?

Answer 14

Clostridial neurotoxins are a group of potent bacterial toxins produced by various strains of Clostridium bacteria. They are known to cause botulism and tetanus, two serious and potentially fatal diseases. These toxins are composed of a light chain and a heavy chain, which work together to block neurotransmitter release at the neuromuscular junction, leading to paralysis and muscle weakness.

There are several different types of neurotoxins

Question 15

Talk about infant botulism

Answer 15

It is the most common form of the disease
Bbabies under 6 months are more susceptible
Floppy baby syndrome

Question 16

Why and how do clostridial toxins only take up neurons

Answer 16

Clostridial neurotoxins, specifically target and enter neurons because they are taken up by endocytosis
a selective process that occurs mainly in cells that have a synaptic membrane.
This membrane is found only in neurons and is specialized for the release and uptake of neurotransmitters.
The clostridial toxins are taken up by the synaptic membrane of neurons through a receptor-mediated endocytosis process, where they are then transported to the cytoplasm and eventually cause damage to the neuron.
Therefore, the clostridial toxins can only affect neurons because they require the specialized synaptic membrane for uptake.

Question 17

Why do Clostridial neurotoxins cleave different SNAREs ?

Answer 17

by cleaving specific SNAREs, Clostridial neurotoxins can selectively target and affect the function of specific types of neurons. For example, tetanus toxin cleaves VAMP2, which is mainly expressed in inhibitory neurons, while botulinum toxin types A, B, and E cleave SNAP-25, which is expressed in both excitatory and inhibitory neurons.

Question 18

What is different about tetanus and botulinum ?

Answer 18

Tetanus and Botulinum toxins have a similar mode of action, which is to cleave SNARE proteins and inhibit neurotransmitter release, they have the capacity to intoxicate different neurons.

Question 19

Whata re the clinal uses of Botulinum ?

Answer 19

Cosmetic uses (Botulinum A)

Botulinum A can be used to non-surgically treat Strabismus

botulinum B can be used to treat cervical dystonia

Strabismus, blepharospasm, hemifacial spasm, cervical dystonia, axillary hyperhidrosis, over active bladder, GI tract disorders, sialorrhea, temperomandibular disorder and limb spasticity

Most products are based around Botulinum A and target SNAP25. Treatment last for several months

Botulinum market is currently valued at early 5 billion dollars

Question 20

What are the clinical uses of tetanus ?

Answer 20

Can’t make medicines based around tetanus as everybody is vaccinated against the toxin.