SNARES 2 Flashcards
what does snare motif consist of?
coil-coil domains
coild wrap around each other to form parallel coil-coil complex
what domains does syntaxin have?
TM domain to anchor in membrane (PM?)
Habc domain towards N-terminus
what are R and Q SNARE motifs?
R SNARES are V SNARES (vAMP) (arginine residues)
Q SNARES are T SNARES (syntaxin, snap 25) (glutamine residues)
WHat are confirmations of syntaxin?
- closed formaiton - when Habc curved round to keep syntaxin in closed formation
- needs to transition into open confirmaiton to bind and form a snare complex
what is the snap-25 linker?
it is between the 2 snare motifs on snap-25.
- has 4 cysteine residues and is palmitylated to anchor into the PM)
(as snap-25 has no TM domain)
what is a SNARE pin composed of?
3 Q snare motifs
1 R snare motifs
7s?
what is the support for SNAREs involvement in membrane fusion?
- can reproduce what occurs in vivio in vitro
- syntaxin 1 KO - animals die - can’t breathe? muscular NMJ require secretion/fusion of vesicles
- patch clamp can measure membrane fusion and neurotransmission
give 2 popular systems for patch clamp techniques
1) isolate hippocampus - hypocampal neurons form autapses (synapse on selves) - looks at transmission via patch clamp
2) chromaffin cells (release adrenaline) - can tell if vesicles stuffed into cell by measuring SA of cell but can also do patch clamp - look at transmission
what can cleave SNARES?
tetanus and botulinal toxins (classes of anaerobic clostridial toxins found in soil)
(most powerful toxins - lethal in small amounts)
what is released by clostridial bacteria + what does this contain?
- 150 kDa peptide released by bacteria
- contains a heavy chain (100kDa)which contains receptor binding domain required for internalisation into the cell.
- contains light chain (50 kdA) which contains enzymatic domain for cleaving SNAREs (metallo-endopeptidase domain)
what do tetanus and botulinum cause?
tetanus - paralysis
botulinum - flaccid paraylisis
(synaptic transmission abolished)
give steps in botulinum neurotoxin in cleaving SNAREs
1) heavy chain binds to specific sites on the surface of neurons (presynaptic terminal)
2) heavy chain is internalised by presynaptic neuron into endosomes (acidic environment)
3) Acidic environment causes rearrangement of toxin and heavy chain forms a channel out of endosome
4) light chain escapes into cytosol through this channel
5) light chain cleaves free/uncomplexed SNAREs
can stay in cells for a long time
causes mild muscle paralysis
how many mammalian snares have been identified?
38
what is the subcellular locaiton of mammalian snares?
different snares/isoforms found in different compartments of the cell .
- although 4 snare motifs are always required to form snare pin (7s)
what happens when SNAP-25 is knocked out?
- although snares can substitute for one another (e.g. snap-23) some functionality is lost
