SNAREs Flashcards
how to visualise secretory vesicles
electron microscropy
3 main approaches to identify machinery of vesicle transport
- Biochemical reconstitution ie breaking apart
- Yeast Genetics
- Cloning
role of NSF
ATPase required for membrane fusion
role of SEC18
- Binding protein
- Required for vesicle-mediated transport
- Fusion protein required for the delivery of cargo proteins to all compartments of the Golgi stack
Rothman’s snare hypothesis
1) SNAREs for each transport step within the cell.
2) SNAREs should provide specificity to vesicle transport.
3) SNAREs should be sufficient to drive lipid bilayer fusion.
4) Proposed that NSF and ATP hydrolysis catalyses membrane fusion - wrong
what do snares do
- zip up to drive vesicle and disrupts lipid bilayer
what is syntaxin
- part of SNARE complex
- proteins localized to the plasma membrane of the presynaptic active zone
- act as a regulatory domain
- bind synaptotagmin on SVs in response to calcium entry
common features of SNARE proteins
- target membrane
- small 14-40kDA
- at least 1 coiled coil or snare motif
- generally c-terminally anchored
animal homologs of shibire, comatose and paralytic
- shibire: dynamin (pinches of vesicles of membrane and recycling)
- comatose: NSF
- paralytic: α-subunit of voltage-gated sodium channel
VAMP2 KO mice phenotype
Die at birth. Loss of synaptic transmission
Syntaxin1A KO mice phenotype
No gross abnormalities. Subtle defects in synaptic transmission
Syntaxin2A KO mice phenotype
Die after birth. Reduced synaptic transmission
SNAP25 KO mice phenotype
Die at birth. Loss of synaptic transmission
human diseases associated with VAMP2 mutation
Neurodevelopmental disorder with hypotonia and autistic features with or without hyperkinetic movements
human diseases associated with SNAP25b mutation
Neurodevelopmental disorder with seizures, intellectual disability, severe speech delay, and cerebellar ataxia
human diseases associated with SNAP29 mutation
Cerebral dysgenesis, neuropathy, ichthyosis, and palmoplantar keratoderma syndrome (CEDNIK syndrome)
human diseases associated with Syntaxin11 mutation
Familial hemophagocytic lymphohistiocytosis type 4 (FHL4)
Heterozygous mutations in VAMP2 cause
-
hypotonia
- characterized by axial hypotonia, learning disability and autism
what is familial hemophagocytic lymphohistiocytosis
- Rare disease of the immune system mainly affecting kids
- over proliferation of t cells, k cells, b cells, macrophages
- mutation in several genes
protein mutations linked to FHL4
- reduced levels of STX11
- loss of Syntaxin11 causes defective degranulation from cytotoxic Tcells by unclear mechanism
role of munc18-2
- binds to STX11
- mutation causes FHL
name 2 potent clostridial neurotoxins and their effect
Clostridium tetani: tetanus (lock jaw) = muscle spasm
Clostridium botulinum:botulism = floppy
structure of clostridial neurotoxins
- targeting domain
- section allowing entrance to neurones
- translocation domain
- allowed to be uptaken by endosomes
- protease domain
- cleaves snares
clostridial toxin uptake to neurones
- toxin binds to membrane
- taken in via endocytosis
- endosome becomes acidic
- endopeptidase is mvoed out of endosome and cleaves syntaxin and snap25
Botulinum neurotoxins and their clinical uses
- cosmetic uses (small doses)
- high efficacy, tolerance, longevity and satisfactory safety profile
- Most products are based around Botulinum A and target SNAP25. Treatment last for several months\
- muscular diseases can be treated using the toxin
- Can’t make medicines based around tetanus as everybody is vaccinated against the toxin.
