Lecture 12: Bacterial Toxins I

Question 1

What is an endotoxin

Answer 1

Non-Protein Toxin
Antibiotic could be considered an endotoxin
Usually a part of the bacterial structure, such as LPS (TL4 recognizes)
Is it a virulence factor, or is it just part of the structure that the host responds to.

Question 2

What is an exotoxin

Answer 2

Protein Toxin:
It is a component that acts directly as a toxin to help promote the reproducing and sustainability of the pathogen in its host. There are three types of exotoxins. I, II, III. They act extracellularly, act on the membrane, or act intracellularly.

Superantigens work to increase MHC/TCR binding. Bridging the two. Can be detrimental to the host as it is 2000x increased.

Pore-forming or membrane hydrolyzing

and then A-B toxins. A for activity, B for binding, T for translocation.

Question 3

differences between endotoxins and exotoxins

Answer 3

Endotoxins are non-protein, usually strutural components of the pathogen. Such as LPS from gram-negative bacteria

Exotoxins: protein toxin.

Question 4

What is the genetic source of toxins

Answer 4

Correlates to the toxin type and where It acts.
Type I: mixed chromosomal/extra-chromosomal
Type II: mostly chromosome
Type III: prophage/plasmid

Question 5

Compare the 3 types of exotoxins

Answer 5

superantigen: MHC + TCR, increase the binding duration and signal intensity. Acts extracellularly

Pore-forming or membrane hydrolyzing. Act to lyse the cell.

A-B Toxins: Acts intracellularly to inhibit protein actions.
Translational repression, g-coupled protein inhibition, cytoskeleton inhibition.

Question 6

Pore-forming vs membrane hydrolyzing toxins

Answer 6

Pore-forming: binds to membrane surface receptor, oligomerizes to form a pore, and causes lysis.

Membrane hydrolyzing: toxin binds to surface receptors, crosses the membrane, and cleaves phospholipids at specific positions.

Question 7

Describe Cellular entry for A-B toxins

Answer 7

B subunit binds to cellular receptor. Facilitates entry for the A subunit.
B subunit mediates, and the T subunit, the translocation of the A subunit to its target.

Question 8

contrast the properties of A and B subunits

Answer 8

A subunit: the toxic part of the toxin

B subunit: delivers the toxin to the target

can have multiple subunits for each A and B.

T domain, part of B domain. The A subunit needs to translocate across a membrane. Special activity via the T subunit, which is part of the B.

A for activity
B for binding
T for translocation

Question 9

Type II exotoxin

Answer 9

acts on the membrane of the host cell

ie. pore-forming toxin

Question 10

Type III exotoxin

Answer 10

acts intracellularly

ie. A-B type toxins

Question 11

Type III exotoxin

Answer 11

acts intracellularly

ie. A-B type toxins

Question 12

Best known superantigen (type I) toxin

Answer 12

Staphylococcus aureus.
Superantigens
Bind to MHC class II and to TCRs

The result is excessive cytokine signaling and release

The superantigen bridges the TCR and MHC binding.
Increases activation energy of the Tcell, 2000 fold.
excessive cytokine release and inflammation

Question 13

Hemolysin or Cytolysin

Answer 13

Types of pore-forming type II exotoxin.

Question 14

Hemolysin or Cytolysin

Answer 14

Types of pore-forming type II exotoxin.

Question 15

Type III retrograde transport

Answer 15

Some type III A-B subunit toxins have developed the ability to no be degraded when retrograde transport happens.

Question 16

Type III retrograde transport

Answer 16

Some type III A-B subunit toxins have developed the ability to not be degraded when retrograde transport happens.

Question 17

Best known activity for toxic activity of the A subunit

Answer 17

ADP-ribosylation. 
Sticks an ADP ribose on proteins 
renders proteins inactive. 
"translation machinery" 
G-protein coupled signaling 
cytoskeleton protein inhabiting