Unformatted text preview: ck induced by toxic shock syndrome antigen of Staph Induce systemic reactions: fever, widespread clotting, shock EXOTOXINS: Based on SITE OF EXOTOXINS: Based on SITE OF ACTION: Cytotoxins: inhibit a cell function or cause cell death: Corynebacterium diptheriae: next slide Neurotoxins: inhibit nerve transmission (Cytolysins (Cytolytic toxins) are cytotoxins that cause cell death by lysis): Ex alpha toxin of Staph.
Examples: tetanus and botulinum toxin Enterotoxins: alter permeability of intestinal epithelium Examples: Cholera and Staph aureus food poisoning enterotoxin (also superantigen) Diptheria toxin is an A-B toxin that inhibits a cell function: protein synthesis
1. B promotes binding of toxin to cell membrane
2. When it binds to cell membrane, it is cleaved and A is internalized.
3. A catalyzes ADP-ribosylation of elongation factor 2 (EF-2) and it no longer
aids the transfer of amino acids to growing polypeptide chain. Ends protein
Only a single toxin molecule is needed to kill a cell.
Diptheria toxin is formed only by strains of Corynebacterium diptheriae cells that
are lysogenized by phage beta. Lysogenic versus Lytic
Lysogenic versus Lytic Staphylococcal alpha toxin: a pore forming cytotoxin that is produced by growing Staphylococcal cells
Released as a monomer, 7 subunits oligomerize in cytoplasmic membrane forming a pore in target cell
Pore releases the contents of cell allowing the influx of extracellular material & efflux of intracellular material
Eukaryotic cells swell & lyse; in erythocytes, hemolysis Figure 21.18
Figure 21.18 Anthrax
Anthrax Made of Three parts: each individual anthrax toxin protein is, in fact, nontoxic. A/B toxin. Actually A2B B component called protective antigen (PA)
A components: Edema factor (EF): causes swelling
Lethal factor (LF): causes cell death PA binds to anthrax receptor and then binds the EF & LF (Endocytosis brings complex into cell) Low pH of endosome causes conformation changes and allows EF & LF to enter cytosol and cause damage).
Enzymatic activities lead to altered signaling pathways which cause macrophage functions to be impaired and ultimately apoptosis of the target cell. Botulinum toxin: o
o o o 7 distinct toxins2 of which are encoded for by genes on lysogenic bacteriophages
Toxin binds to presynaptic terminal membranes at nervemuscle junction, blocking the release of acetylcholine required for transmission of nerve impulse to muscle. Muscle contraction inhibited & have flaccid paralysis 1 mg kills 1 million guinea pigs o Tetanus toxin:
2 polypeptides, fixed to nerve synapsis (inhibitory interneurons), blocks release of glycine, a factor that induces muscle relaxation •
Relaxation signal is blocked & paired muscles both contract •
Spastic paralysis, twitching paralysis Exotoxins Enterotoxins
o Enterotoxins alters permeability of intestinal epithelium; causes massive secretion of fluid into the intestinal lumen causing diarrhea
o Staphylococcus aureus vomiting, diarrhea: also super AG
Vibrio cholera •
• • Cholera toxin: 3 polypeptides (A1, A2, B)
B toxin involved in binding to ganglioside GM1 in e...
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- Fall '13
- Virulence factors, Protein biosynthesis, elongation factor