L2 SNAREs 1 Flashcards
What do SNAREs do
facilitate membrane fusion and release of the contentsof vesicles
Which steps offusion are SNAREs required in
all of the steps
What are the 3 main SNAREs and where are they
VAMP - on the vesicle
SNAP25 and Syntaxin on the other membrane
List 5 physio systems that use vesicle fusion
- Neurons - neurotransmitters
- Secretory granules - endocrine and exocrine functions of the pancreas(secreting and insulin)
- Secretion of serum proteins (albumin from hepatocytes and antibodies from plasma cells)
- Mucus secretion (epithelial mucosal cells)
- Intracellular transport of proteins between organelles in all cells
Golgi function
Protein sorting and packaging into secretory vesicles
3 pathways for proteins from the Golgi
- Regulated secretory pathway
- Constitutive (unregulated) secretory pathway
- Signal-mediated diversion to lysosomes (via endosomes)
Requirements for the regulated secretory pathway
- A signal has to be released and stimuate the release
- Regulatedby intracellular secretory pathways
= Used for signals like hormones and neurottransmitters
How was NSF discovered
N-ethylmaleimidie was found to ibhibit the rate of transport. NSF was the protein targeted by NEM
What is NSF
N-ethylmaleimide Sensitive Factor - an ATP-ase
What does SEC 1 encode
SNARE binding protein
What does SEC 17 encode
alpha-SNAP
What does SEC 18 encode
NSF
Pacific Electric Ray neuron pros
very big neurons
What is Rothman’s SNARE hypothesis
- There are SNAREs for each step of transport within the cell
- SNAREs should provide specificity to vesicle transport
- SNAREs should be sufficient to drive lipid bilayer fusion
- Proposed that NSF and ATP hydrolysis catalyses the membrane fusion - THIS IS WRONG
What is the shape of the neuronal SNARE complex
Parallel coiled coil
NSF function
unzipping the SNARE complex after membrane fusion
Is NSF required for fusion
No, only for unzipping
Why are SNAREs important
Membranes are both hydrophobic and charged, so it is energetically unfavourable for them to fuse - SNAREs provide the energy for fusion
Ratio of R and Q snares
3Q:1R
What would a mutation in one of the Q/R components do
Inhibit the function of the whole complex
How specific are SNAREs
- Fuse only with SNAREs with the correct Q:R ratio
- A bit promiscuous but generally interact with SNAREs from appropriate membranes
Common features of SNARE proteins
Conserved topology:
generally small, anchored by the C-terminal and have at least 1 SNARE motif
Are SNAREs sufficient for membrane fusion?
Yes, but it occurs VERY slowly (almost no fusion)
Ca2+ enhances the rate of fusion
What is teh extended part of syntaxin and what does it do
It’sthe regulatory part of the protein - if cut off, vesicle fusion won’thappen
