SNARES 2 Flashcards
What are the componants of the 20S complex?
NSF, SNAP, vAMP, Syntaxin and SNAP25
What forms first in the 20S complex and then what events occur?
The 3S complex forms consisting of SNAP25, vAMP and Syntaxin.
Once the 3S complex forms, SNAP binds, allowing NSF to bind and then the configuration is broken by NSF using ATP —> ADP + Pi
Why do vesicles have to carry a specific SNARE?
Why do target membranes often have more than one SNARE?
Vesicles carry a specific SNARE to allow them to interact with a particular target.
Often target membranes have more than one SNARE so that they can accommodate more than one vesicle type.
Outline structure of Synaptobrevin - - what domains are present and why is it therefore an ‘R’ SNARE?
Synaptobrevin has a SNARE domain which consists of highly conserved coil-coil a helices with an ARGANINE residue at the centre – hence Synaptobrevin is an R SNARE.
Also has a TRANSMEMBRANE domain
Outline structure of Syntaxin - - what domains are present and why is it therefore an ‘Q’ SNARE?
Has a SNARE domain which consists of highly conserved coil-coil a helices with a GLUTAMINE residue at the centre hence the name Q SNARE.
Also has a Habc domain and a transmembrane domain
What is the purpose of the Habc domain and how does it work?
Regulatory domain - has a regulatory feature!
It is able to fold back to obscure the SNARE motif of the SNARE protein –
OPEN configuration - Habc domain is flipped up away from the SNARE motif
CLOSED configuration - SNARE motif is hidden so prevents SNARE coils from forming
Outline structure of SNAP25 - - what domains are present and why is it therefore an ‘Q’ SNARE?
Has 2 SNARE motifs - QB and QC. It is attached to the plasma membrane by PALMITOYLATION of 4 CYSTEINE RESIDUES
What happens to SNARES during the zippering reaction?
SNARES wrap around each other and join together at their amino terminuses - ONE OF THE STRONGEST STRUCTURES IN BIOLOGY
Outline the current model of how SNARES join the plasma membranes ?
- SNARES dock vesicles to the plasma membrane
- When SNARES coil around each other, other proteins in the membrane block zippering reaction from occurring
- The SNARES that are ‘clamped’ in place must have their clamps removed – then membranes are pulled together and the zippering reaction completes
SNAP25/Syntaxin – how does it work to initiate helix formation and SNARE zippering reaction?
-SNAP25 and Syntaxin form a dimer and act as an acceptor for vesicular Synaptobrevin (or a ‘docking’ platform).
Once synaptobrevin binds the HELIX forms.
What Support is there for the current SNARE model?
MICE AND WORM STUDIES - knockouts of SNAREs show secretory defects
YEAST HOMOLOGOUS PROTEINS - mutants in these show secretory defects
Protein interactions can be reproduced in vivo
Neurotoxins cause muscle paralysis and interfere with NT release and exert their actions on SNAREs
What are neurotoxins and where do they come from?
What is their structure / mechanism of action (light and heavy chain) ?
TETANUS and BOTULINUM and produced by anaerobic bacteria.
150dk peptide is released by bacteria consisting of a light and heavy chain
HEAVY CHAIN - the receptor binding domain. Needed to get inside neurons so neurotoxin can exert action
LIGHT CHAIN - enzymatic domain of the neurotoxin / the part that cleaves the SNARE protein
How many types of mammalian SNAREs are there?
38 mammalian SNAREs with common structural features.
SNAP proteins - outline some types and their functions?
SNAP25 - regulated secretion
SNAP23 - constitutive secretion, INSENSITIVE to neurotoxins
SNAP29 - function not 100% known but thought to be involved in LTP??
Why are knockdown and reconstitution experiments useful in the context of SNAREs?
- Can be used to identify specificity of SNARE interactions
- Provide insight into the specificity and function of molecular interactions
