Mimm 465: Lecture 13 Moual

Front 1

What was the first bacterial virulence factor identified?

Back 1

Exotoxin

Front 2

Which toxin did Roux and Yersin isolate?

Back 2

Diphtheria toxin

Front 3

What are exotoxins?

Back 3

Toxic ptns SECRETED from a living bacterium
(exotoxins are very diverse)

Front 4

What do exotoxins do?

Back 4

Act on host cells
Have deleterious effects on the host

Front 5

What are the different type of exotoxins?

Back 5

1) Surface-acting toxins
2) Pore forming toxins
3) AB toxins
4) Types III and IV secretions

Front 6

How do surface-acting toxins work?

Back 6

Bind a receptor on the cell membrane
Triggers intracellular signals

Front 7

What do pore-forming toxins do?

Back 7

Punch a hole in the bacterial membrane

Front 8

What are AB toxins?

Back 8

A lot of diversity
Can be 1 ptn or a complex of multiple ptns
Internalized by host endosomes and end up in Cytoplasm
-Other AB toxins go through retrograde transport to the Golgi and ER

Front 9

How do toxins use Type III and IV secretion systems to get into the cell?

Back 9

Use the secretion systems to inject themselves into the cell

Front 10

What do superAgs interact with?

Back 10

MHC II and TCRS (simulataneously)

Front 11

What happens once a SAg interacts with its receptors?

Back 11

Activates T cell
Get massive production of inflammatory cytokines (TNFα and IL-12)
Can lead to septic shock

Front 12

Which bacteria are the main producers of SAgs?

Back 12

S. aureus
Strep pyogenes

Front 13

What carries most of the genes for the SAgs in these bacteria?

Back 13

Bacteriophages
.: SAgs are only in a subset of strains

Front 14

What is the prototypical SAg?

Back 14

Toxic Shock Syndrome Toxin-1 (TSST-1)
Produced by some strains of S. aureus

Front 15

What is the mechanism of action of SAg binding?

Back 15

SAg bind to MHC II and TCR sites away from the peptide binding sites
Binding can occur even in the absence of presented Ag
SAgs usually bind Vβ region (but doesn't bind all regions .: doesn't activate all T cells)

Front 16

What do type II toxins do (pore-forming toxins)?

Back 16

ptns that induce lysis of host cells

Front 17

Describe large-pore-forming toxins.

Back 17

Bind to CHOLESTEROL on host cell mb
Monomers polymerize to form very large pores (40-80 subunits, up to 35nm in diameter)
Cell mb becomes PERMEABLE to solutes and macromolec
->Results in cell death

Front 18

Describe SMALL-pore-forming toxins.

Back 18

-Secreted as MONOMERS that bind cell surfaces
-monomers oligomerize into HEPTAMERS that insert into the mb
-formation of small pores (1-2.6 nm)
-molec with mass lower than 2000 Da can diffuse (still enough to cause cell death)

Front 19

What are the family of related ptns secreted by S. aureus?

Back 19

α- hemolysin
γ- hemolysin
leukocidin

Front 20

What is the domain organization of AB toxins?

Back 20

B fragments: transport catalytic A fragment into cells
-AB toxins have a single ptn (prototype: Diphtheria toxin (DT))
-AB5 toxins have 6 non-covalently bound ptns (prototype: cholera toxin (CT))
-Binary toxins are ptns that aren't assoicated in solution, but do ass't when bind to host cells (prototype: Anthrax toxin -> edema toxin and lethal toxin that ass't with the protective Ag)

Front 21

Look at figures pg 7

Back 21

look at figures pg 7

Front 22

What is diphtheria?

Back 22

Normally an infection of the throat caused by a bacterium (Corynebacterium diphtheriae)

Front 23

What kind of bacteria is Corynebacterium diphtheriae?

Back 23

G+
Non-spore forming
Non-motile
Aerobic rod

Front 24

Are all Corynebacterium diphtheriae strains toxic?

Back 24

No

Front 25

What carries the tox gene encoding DT?

Back 25

Family of corynebacteriophages
-Toxigenic strains of Corynebacterium diphtheriae have been lysogenized by these phages

Front 26

What carries the cholera toxin?

Back 26

Cholera toxin phage (CTXφ)

Front 27

How is the toxin activated?

Back 27

3 domains: C, T and R
Proteolytic cleavage at Arg 193
Reduction of S-S in the the cytoplasm of the host cell
Fragment A is released into the cytoplasm (C domain)
Frag B has translocation domain, responsible for translocation of catalytic frag from endosome into cyto

Front 28

Describe the 1st step of toxin activation. (Binding to the Host Cell Receptor)

Back 28

R-domain (part of B chain) binds to specific receptor on host cell surface
Receptor is the heparin-binding epidermal growth factor (HB-EGF) precursor

Front 29

Describe the 2nd step of toxin activation (Endocytosis and Translocation)

Back 29

-Endocytosis of toxin-receptor complex
-Formation of a vesicle (pH goes from 7 -> 5.5)
-Acidic pH in the endosome promotes a conformational change (T-domain) that inserts the toxin in the vesicle mb
-A chain translocated into the cytoplasm
-Reduction of the disulfide releases A-chain into cytoplasm

Front 30

Look at figure pg 11: Enttry of AB toxins into target cells

Back 30

Look at figure pg 11: Enttry of AB toxins into target cells

Front 31

Describe the enzymatic activity of the toxin

Back 31

In the cytoplasm, A-chain of DT catalyzes the ADP-ribosylation of EF-2
In euk: EF-2 participates in elongation of Translation
ADP-ribosylation inactivates EF-2 and blocks ptn synthesis
ADP-ribosylation occurs at diphtamide (derivative of histidine)
A single molecule of A-chain is enough to kill one eukaryotic cell

Front 32

How toxic is the A-chain?

Back 32

Single molec of A-chain is enough to kill one eukaryotic cell

Front 33

What is a toxoid?

Back 33

Toxin rendered nontoxic but still immunogenic by chemical modification or heat treatment
-> Use to make a vaccine

Front 34

What is the Diptheria toxoid?

Back 34

Toxin treated with formaldehyde (HCHO)
HCHO reacts with Lys amino gps and forms internal cross-links

Front 35

Summary

Back 35

Production of toxin
Secretion from bacteria
Binding to receptor through B fragment
Endocytosis
Release fragment A
Recognition of EF-2
->Can no longer make proteins .: cell death

Front 36

What is the usage of exotoxins?

Back 36

Study cellular processes (cholera and pertussis used to study GPCR signalling)
Modified exotoxins used as carriers for Ag delivery in mucosal vaccines
Modified exotoxins used as vehicles for drug delivery
Some exotoxins used as therapeutics and cosmetics

Front 37

Describe the sec-dependent secretion system.

Back 37

Type V:
ptn contains β-barrel, through which the passensger domains go through (cuz barrel extends through mb)
Can get cleaved or β-barrel can have its own cleaving system
Type II
ptn made in cytoplasm
exported to periplasm, then sent outside

Front 38

Describe the Sec independent paths

Back 38

Type IV, III and I
Effector ptns secrete directly into cytoplasm of host
Effector ptns interfere with host cell proteins and change normal host cell fct
promotes internalization of bacteria to get into host cell cytoplasm

Front 39

Look at figure pg 13

Back 39

look at figure pg 13

Front 40

Describe type III & IV secretion systems

Back 40

Some G- bacteria use a different strategy to deliver their toxins
Directly inject toxin effectors into host cell cytoplasm

Front 41

What are type III secretion systems related to?

Back 41

Flagella (Salmonella enterica)

Front 42

What are type IV secretion systems structurally related to?

Back 42

Conjugation apparatus (legionella pneumophila and Heliobacter pylori)