bacterial toxins

Question 1

what are endotoxins and what are their structure

Answer 1

LPS
O antigen, core polysaccharide and lipid A
- lipid A is endotoxin

Question 2

can you make a vaccine against LPS

Answer 2

No - not a protein

Question 3

steps of pore forming toxin action

Answer 3

Inactive monomer that binds to receptor (usually protein, can be lipid) on membrane

Other monomers join the monomer to make a polymer to from a pore

Influx of water, efflux of ATP, large molecules
example: Streptolysin O

Question 4

function of phospholipase

Answer 4

targets lipids
Phospholipase C, haemolysin for C. perfringens that targets the cell membrane of red blood cells

Question 5

Diphtheria toxin

Answer 5

A-B toxin
Single chain that is produced as a pre-curser protein that is cleaved, and joined by disulfide bond

1. toxin taken into cell by receptor mediated endocytosis
2. disulfide bond reduced when taken into endosome, breaks into A and B subunit
3. A subunit ADP-ribosylates elongation factor 2 in ribosome -> stops protein synthesis

Question 6

What do ADP-ribosyltransferases do

Answer 6

Toxin strips ADP ribose from NAD+ and delivers it onto target

Question 7

Anthrax toxin structure

Answer 7

plasmid encoded, multi chain A-B toxin
two A subunits: adenylate cyclase (EF)
and zn2+ dependent endopeptidase
^ structurally unrelated except for where the B subunit binds
protective antigen (B subunit)

Question 8

anthrax toxin

Answer 8

Furin (cellular protein) cleaves bound PA into PA63 -> active form

Oligomerises
- 7 monomers

Binds with EF and LF

Receptor mediated endocytosis

Low pH of endosome causes conformational change where B subunit inserts itself into the endosomal membrane, channel for a subunits

EF = cellular ATP into cAMP causing an increase in fluid
LF inactivates MAPKK leading to apoptosis

Question 9

mycolactone

Answer 9

produced by mycobacterium ulcerans
(buruli ulcer)
not a protein
Toxin is immunosuppressive, kills cells
Acts as an aesthetic, don’t feel pain in ulcer

Causes actin polymerisation, stopping cellular adherence, cells dissociate from each other and die

Question 10

tilivalline

Answer 10

cause clips in DNA, when in the gastrointestinal tract it undergoes condensation with indole = tilivalline
Enterotoxin that binds to tubulin, stabilises microtubules, causing mitotic cell arrest and cell death