SNAREs Flashcards
What are examples of membrane fusion? (5)
- Synaptic vesicle fusion
- Secretory granule fusion (endocrine and exocrine pancreas)
- Secretion of serum proteins (antibodies, albumin)
- Mucus secretion
- Intracellular transport of proteins between organelles
What are the components of the neuronal SNARE complex? (3)
- VAMP (V-SNARE)
- Syntaxin (T-SNARE)
- SNAP25
What is the structure of the SNARE complex? (6)
- VAMP/V-SNARE is on the vesicle
- SNAP25 and syntaxin/T-SNARE are on the target membrane
- SNAP25 has 2 coiled-coil (SNARE) domains, VAMP and syntaxin have 1 (3Q:1R)
- Proteins zipper up via hydrophobic domains
- Syntaxin folds back on itself to form a regulatory domain
- Salt-bridge forms at the zero layer of the SNARE complex
What are the 2 types of SNAREs?
- R SNAREs
- Q SNAREs
What are R SNAREs? (2)
- Have an arginine in the position of the zero layer of the SNARE complex
- i.e. VAMP/V-SNAREs
What are Q SNAREs? (2)
- Have a glutamine in the position of the zero layer of the SNARE complex
- i.e. syntaxin/T-SNAREs and SNAP25
What is the SNARE ratio in the complex?
3Q:1R is conserved in all complexes
Which components provide the specificity of membrane fusion? (2)
- SNAREs mostly interact with SNAREs from the appropriate membranes but show some promiscuity
- Additional machinery e.g. rabs, coat proteins, tethers contribute to specificity
What is NSF? (3)
- Unwinds the SNAREs after fusion for recycling
- Requires ATP hydrolysis
- Involved in the 20S complex
What are the features of SNARE proteins? (2)
- Small C-terminally anchored proteins
- All contain at least 1 coiled-coil domain
How does fusion occur? (4)
- SNARE complex zippers together to bring the membranes close enough to overcome the repulsion of the lipid bilayers
- Destabilisation of the membranes for fusion
- SNAREs end up on the same membrane
- NSF unzips the SNAREs for recycling
What is the evidence for NSF in drosophila? (3)
- Identified temperature sensitive drosophila mutants
- Comatose mutant was paralysed at the restrictive temp, had mutant NSF
- Comatose flies have an accumulation of docked vesicles because the SNAREs can’t be recycled
What is the phenotype of a VAMP2 knockout mouse? (2)
- Die at birth
- Loss of synaptic transmission
What is the phenotype of a syntaxin1A knockout mouse? (2)
- No gross abnormalities
- Reduced synaptic transmission
What is the phenotype of a syntaxin1B knockout mouse? (2)
- Die after birth
- Reduced synaptic transmission
What is the phenotype of a SNAP25 knockout mouse? (2)
- Die at birth
- Loss of synaptic transmission
What is caused by heterozygous mutations in VAMP2? (2)
- Neurodevelopment disorder with hypotonia (floppy baby syndrome)
- Mutations in the coiled-coil domains
What is a liposome fusion assay? (2)
- Membrane fusion shown by an increase in fluorescence
- Can introduce mutations and see how it affects membrane fusion
What is caused by heterozygous mutations in syntaxin 11? (3)
- Familial hemophagocytic lymphohistiocytosis (FHL4)
- Syntaxin 11 is involved in the immune system
- Killer T-cells are unable to secrete lytic granules to kill infections
Why are severe diseases useful to research?
Gives you insight into how fundamental proteins work
What diseases are caused by neurotoxins? (2)
- Tetanus
- Botulism
What is the structure of clostridial neurotoxins? (3)
- Targeting domain (binds to neuron)
- Translocation domain (get into the neuron)
- Protease domain (cleaves SNAREs)
What is the target of BoNTA?
SNAP25
What are the symptoms of tetanus? (3)
- Go rigid
- Intense muscle spasms
- Stops the action of SNAREs in inhibitory neurons
What are the symptoms of botulism? (3)
- Go floppy (paralysis)
- Hypotonia (floppy baby syndrome)
- Stops the action of SNAREs in the neuromuscular junction
What are the clinical uses of botulinum neurotoxins? (3)
- Cosmetic uses
- Strabismus, blepharospasm, overactive bladder, muscle spasticity, potentially chronic pain etc.
- Most products based around Botulinum A and SNAP25
