Lecture 3 Flashcards
(19 cards)
What are the two types of organism that use toxins?
Venomous; produced by pathogen/predator as a tool to attack their host/prey, and poisonous; produced as a means of defence
What are the four Clostridia interactions with humans?
C. botulinum; botulism and food poisoning
C. difficlile; pseudamembranous colitis
C. perfringens; gas gangrene, uterine infections
C. tetanus; Paralysis form infected wounds
What type of paralysis is caused by Botulinum intoxication?
Flaccid paralysis
What type of paralysis is caused by tetanus intoxication?
Rigid paralysis
Describe the clostridium toxins
Secreted as 100kD single chain proteins, which are clevaed into heavy and light chains; heavy chian has translocation and binding domains
Where is the site of action of the toxins?
Both cellular and intracellular, therefore must;
Bind to their target cell
Translocate to the interior of the cell
Find and Modify their intracellular target
What role does each domain play?
Heavy chain binding domain (Hc); extracellular binding domain Heavy chain translocation domain (Hn); translocation domain Light chain (LC); enzymatic domain
What does the Hc domain bind to?
Ganglioside; Carbohydrate modified sphingolipids found on the external leaflet of the plasma membrane
How do clostridial toxins intracellularise?
via endocytosis, possibly through interaction with synaptotagmin
How is the LC then released?
pH dependent membrane translocation; Hn threads the LC out into the pre synaptic terminal
How was the role of LC shown?
Mochida
Inject LC mRNA (so no heavy chain is present) and see that the toxin inhibits synaptic transmission; probably though accumulating the vesicles
Which neurons do they target?
BoTx targets motor neurons
TeTx targets inhibitory spinal inter neurons, being take up by motor neurons and then using an endosomal vesicle for trafficking.
What homology is seen between the light chains of the Clostridial toxins?
Zinc metalloproteinases; which target structures over sequences
What is the target for TeTx light chain?
Synaptobrevin/VAMP
What proteins do the Clostridium toxins target?
Proteins that hold the vesicle at the plasma membrane; synaptobrevin, SNAP-25 and syntaxin
Which BoTx cleave which targets?
C cleaves syntaxin
A, C and E cleave SNAP-25
B, D, G and F cleave Synaptobrevin
Why can treatment with toxins that cannot cleave a protein block its cleavage by a toxin that could cleave it?
All clostridium toxins are metalloproteinases and will target the SNARE complex; If the toxin cannot cleave it will still be bound to the protein; blocking cleavage by other toxins
What is the SNARE hypothesis?
SNARE proteins on vesicles decide where the fusion will happen
What is a transglutaminase?
An enzyme that covalently links proteins that have glutamate
