Toxins

Question 1

toxins (2)

Answer 1

• kill cells
• alter host-cell functions without killing cells directly

Question 2

type I toxins

Answer 2

• act extracellularly

Question 3

type II toxins (3)

Answer 3

• act on the cell membrane and destroy cell membrane
• cytolytic
• can be enzymatic or non-enzymatic

Question 4

type III toxins

Answer 4

• classical A/B toxins

Question 5

cytolytic

Answer 5

• damage to membranes usually causes host cell lysis or death

Question 6

type II toxins: non-enzymatic (2)

Answer 6

• form large pores/channels in membrane
• cholesterol-dependent cytolysins

Question 7

type II toxins: how are non-enzymatic pores formed (2)

Answer 7

• toxin monomers can bind cholesterol and assemble on surface to form a pre-pore and then insert
• toxin monomer binds cholesterol and inserts into membrane, triggering monomers to bind and form a large pore

Question 8

why does cell/phagosome lysis occur after non-enzymatic pore formation

Answer 8

• water enters the cell/phagosome which causes swelling

Question 9

non-enzymatic type II toxin examples (2)

Answer 9

• streptolysin O
• listeriolysin O (LLO)

Question 10

how does LLO function as a type II, non-enzymatic toxin (2)

Answer 10

• change in pH causes conformational change in the protein
• change allows toxin to insert into phagosome membrane

Question 11

type II toxins: enzymatic damage (3)

Answer 11

• caused by phospholipases
• enzyme removes polar head groups from phospholipid (PlcC activity)
• causes damage to the membrane, and instability leads to lysis

Question 12

what is an examples of a type II, enzymatic toxin and how does it function (2)

Answer 12

• PlcC (phospholipase C)
• removes polar head groups from phospholipids

Question 13

what do type III toxins do (2)

Answer 13

• alter metabolism of the host cell
• exploit or subvert normal host cell processes

Question 14

what are A/B toxins (2)

Answer 14

• B is the Binding component of the toxin
• A is the enzymatically Active component of the toxin that binds to target inside host

Question 15

what kinds of toxins are A/B toxins (5)

Answer 15

• toxins that target protein synthesis
• toxins that alter signal transduction
• toxins that alter actin polymerization
• neurotoxins
• anthrax toxins

Question 16

A/B toxin: forms of B component (3)

Answer 16

• single unit that binds to receptor
• multi-meric structure that is preformed
• mulit-meric structure that forms on the membrane

Question 17

what is diptheria toxins general effect

Answer 17

• targets protein synthesis

Question 18

what bacteria produces diptheria toxin

Answer 18

• corynebacterium diptheriae bacteria that are lysogenic for “beta” phage

Question 19

what kind of toxin is diptheria toxin

Answer 19

• A/B toxin

Question 20

when is diptheria toxin produced

Answer 20

• only produced under low iron conditions

Question 21

diptheria toxin: mechanism of escape into cytosol (7)

Answer 21

• B subunit binds to its receptor, HB-EGF
• entire toxin is taken up by the cell
• toxin is found in the endosome and pH begins to drop
• change in conformation in both A and B subunit
• B subunit forms a pore in the endosome membrane
• A subunit translocates through pore into cytosol as its disulfide bond is reduced, releasing A from B
• A is now in the cytosol

Question 22

diptheria toxin: mechanism of intoxication (3)

Answer 22

• ADP ribosylation
  “A” catalyzes transfer of ADP-ribose from NAD to the target, changing the structure/function of the target (EF-2)

Question 23

steps in ADP-ribosylation (3)

Answer 23

• toxin deprotonates target
• causes target to undergo a nucleophilic attach on NAD
• one bond breaks and a group on NAD is removed, while another bond forms and attaches ADP-ribose from NAD to target

Question 24

why does diptheria toxin cause cell death (4)

Answer 24

• target for ADP-ribosylation is elongation factor 2 (EF2)
• EF-2 activity stops due to modification
• protein synthesis stops as the ribosomes are unable to accept new tRNAs at their A sites
• the cell dies

Question 25

what is the role of EF2

Answer 25

• translocation of the peptide from the A site on the ribosome to the P site on the ribosome

Question 26

what bacteria produces shiga toxin

Answer 26

enterohemorrhagic E. coli

Question 27

what are the symptoms caused by shiga toxin (3)

Answer 27

• diarrheal diseases (dysentery)
• kidney failure
• hemolytic uremic syndrome, which can be fatal

Question 28

what kind of toxin is the shiga toxin and what is the general structure (2)

Answer 28

• A/B toxin
• 1 A subunit, 5 B subunits

Question 29

what is the receptor for shiga toxin B subunits (2)

Answer 29

• gangliosides, which are glycolipids
• specifically gb3 and gb4

Question 30

gb3

Answer 30

• ganglioside glycolipid present in glomeruli of infants and not adults

Question 31

what is shiga toxins general effect

Answer 31

• inhibition of protein synthesis

Question 32

how does the shiga toxin A subunit enter the host cytosol (4)

Answer 32

• B subunits bind to gb3/gb4
• toxin is taken up and trafficked to the ER by retrograde transport
• disulfide bonds holding AB5 are reduced
• A subunit is translocated through Sec translocon to the cytosol

Question 33

what is the shiga toxin A subunit

Answer 33

• N-glycosidase

Question 34

shiga toxin: mechanism of intoxication (4)

Answer 34

• A subunit (N-glycosidase) cleaves adenine from 28S ribosomal RNA (found in ribosome)
• inhibits binding of amino-acyl tRNA to “A” site in the ribosome
• protein synthesis is inhibited
• cell dies