Toxins: BoNT, TeNT, Anthrax Flashcards
clostridial neurotoxins (2)
- botulinum toxin (BoNT)
- tetanus toxin (TeNT)
botulinum toxin (BoNT): bacterium
- clostridium botulinum
botulinum toxin: serotypes
- A-G
BoNT: serotype A (3)
- one of the most potent toxins for humans
- extremely toxic lethal dose
- half life of several months
BoNT: symptoms (2)
- flaccid paralysis; body goes limp
- muscles relax with no contractions
tetanus toxin: bacterium
- clostridium tetani
TeNT: symptoms (2)
- spastic paralysis; muscle spasms
- muscles contracting excessively
C. botulism (3)
- strict anaerobe
- spore-former
- gram positive
botulism types (4)
- food botulism
- infant botulism
- wound botulism
- cosmetic botulism
food botulism (2)
- ingestion of toxin
- bacteria grow in food anaerobically, producing toxin in the food
infant botulism (2)
- ingestion of bacterial spores
- bacteria grows in gastrointestinal tract
wound botulism (2)
- puncture with bacterial spore
- bacteria grows in wound
cosmetic botulism
- injection of toxin for cosmetic reasons
progenitor BoNT structure (3)
- heterodimer
- active (derivative) BoNT protein
- non-toxic protein similar to BoNT (missing active site)
progenitor BoNT structure (3)
- heterodimer
- active (derivative) BoNT protein
- non-toxic protein similar to BoNT (missing active site)
progenitor BoNT: non-toxic component (2)
- likely protects active protein from stomach acids and proteases
- active component eventually dissociates from complex
BoNT structure (3)
- single protein with multiple domains
- HC (heavy chain) and LC (light chain)
- held together via disulfide bonds
BoNT structure: HC
- B subunit
BoNT strucutre: LC (2)
- A subunit
- zinc-endopeptidase, a protease
BoNT target cell
- binds neurons in the peripheral nervous system
BoNT receptor
- “B” subunit binds to pre-synaptic membrane receptors
BoNT: mechanism of intoxication (5)
- HC binds receptor and is taken up into the neuron in an endosome
- disulfide bonds are reduced when pH drops
- LC subunit translocates via HC to the cytosol
- depending on serotype, LC cleaves different SNARE proteins
- fusion of vesicle with pre-synaptic membrane is prevented and no neurotransmitters are released
BoNT: what SNARE proteins are cleaved (3)
- Synaptobrevin
- SNAP25
- Syntaxin
Synpatobrevin (2)
- a VAMP
- found on vesicles containing neurotransmitters
VAMP
- vesicle associated membrane protein
SNAP25
- found on pre-synaptic membrane
Syntaxin
- found on pre-synaptic membrane
what is the molecular results of BoNT intoxication (2)
- blockage of the release of neurotransmitters from neuromuscular junctions in the peripheral nervous system
- BoNT prevents normal contraction of muscles upon stimulation
BoNT: severe condition (2)
- respiratory failure
- death
BoNT: ‘mild’ conditions (5)
- neurological symptoms
- headache
- slurred speech
- double vision
- nausea
BoNT recovery
- over a year, depending on severity
how are BoNT and TeNT related (3)
- structurally very similar
- both are clostridial neurotoxins
- have opposite mechanism/effects
TeNT target cells
- neurons of the central nervous system
what activity does TeNT exhibit (2)
- zinc-endopeptidase activity
- cleaves synaptobrevin (VAMP)
what are the molecular results of TeNT intoxification
- prevention of the release of neurotransmitters from inhibitory neurons in the spinal cord
TeNT mechanism of intoxication (2)
- TeNT must be retrogradely transported to motorneuron cell body
- here, it can access inhibitory neurons of the spinal cord
anthrax toxin bacterium
- caused by bacillus anthracis
B. anthracis routes of infection (3)
- cutaneous
- gastrointestinal
- pulmonary
B. anthracis: cutaneous (3)
- skin lesions
- accounts for 95% of all cases of anthrax
- 20% get septicemia
B. anthracis: gastrointestinal (2)
- rare
- from eating poorly cooked meet from infected animal
B. anthracis: pulmonary (2)
- inhalation disease
- lung is not the site of infection
pulmonary anthrax: within minutes (3)
- spores are inhaled
- spores are phagocytosed by macrophages
- macrophages travel to lymph nodes
pulmonary anthrax: within minutes to hours (2)
- spores germinate in the macrophage and become vegetative bacilli
- bacilli escape from macrophage
pulmonary anthrax: within hours (3)
- bacilli produce toxins and resist phagocytes
- fatal bacteremia, toxemia, or septicemia develops
- edema
pulmonary anthrax: within days (3)
- edema
- meningitis
- death 1-7 days after exposure
pulmonary anthrax: mortality rate
- 80% mortality rate
why do vegetative spores bacilli become spores in the environment
- due to nutrient deprivation
B. anthracis: virulence factors (2)
- capsule
- tri-partite toxin
B. anthracis: capsule virulence factor (2)
- poly-γ-D-glutamic acid
- anti-phagocytic
B. anthracis: tri-partite toxin (2)
- 3 different proteins
- protective antigen (PA), lethal factor (LF) and edema factor (EF)
B. anthracis: tri-partite toxin; protective antigen (2)
- “B” subunit
- heptamer
B. anthracis: tri-partite toxin; “A” subunit
- LF and EF are A “subunits”
what is the receptor for the anthrax PA subunit
- anthrax toxin receptor (ATR)
anthrax toxin: what is the difference between PA and PA’ (2)
- PA’ is made from PA after the host cell protease, furin, cleaves it
- PA is PA83, while PA’ is PA63
anthrax toxin: mechanism of intoxication; adhesion/invasion (4)
- PA binds to its receptors
- PA is cleaved by a host protease (furin), changing into PA’
- PA’ forms a heptamer that LF and EF can now bind to
- the entire complex is endocytosed
anthrax toxin: mechanism of intoxication: survival (3)
- when pH drops to 5, the PA’ heptamers form a pore in the endosome membrane
- LF and EF unfold and translocated through pore
- LF and EF re-fold in the cytosol
anthrax toxin: mechanism of intoxication; LF subunit (2)
- zinc metalloprotease
- cleaves MAP kinases
anthrax toxin: mechanism of intoxication; EF subunit (3)
- calmodulin-dependent adenylate cyclase toxin
- requires host protein calmodulin to become activated
- leads to increase in cAMP levels inside the cell
anthrax toxin: result of LF intoxication (2)
- septic shock
- death
anthrax toxin: results of EF intoxication (3)
- increase in water secretion
- affects chemotaxis of monocytes and neutrophils
- affects phagocytosis, aiding in immune evasion
anthrax toxin: what does EF subunit increase in water secretion affect (2)
- affects water homeostasis in the body
- leads to massive edema
what kind of effects do EF and LT have
- pleiotropic effects
what systems does EF affect (3)
- immune system
- cardiovascular system
- endocrine system
what systems does LF affect (4)
- immune system
- cardiovascular system
- endocrine system
- nervous system
why might anthrax toxin be difficult to study (2)
- they act on key signaling pathways present in many cells types across different systems
- complicates understanding of effects as pathways targeted can cause unique effect for different cells/organs
what was previously found in anthrax toxin that was found to be untrue
- rapid death from LT injection was due to increased cytokine production from macrophages
what was more recently found in anthrax toxin that replaced old research (2)
- hypoxic response proteins rapidly increase after LT injection
- LT predominantly suppresses pro-inflammatory cytokine production
