USMLE Forums banner
1 - 9 of 9 Posts

22 Posts
Discussion Starter · #1 ·
ADP-ribosylation is the addition of one or more ADP-ribose moieties to a protein, a reaction important in cell signaling.
But there are bacterial toxins that act by ADP ribosylation.

Here's the mnemonic

c = Cholera (increases cAMP in intestinal cells causing diarrhea), it acts on G-protein

A = Anthrax

M = rotated E = E Coli (heat stable enterotoxin)

P = Pertussis toxin

speaking of the heat labile toxin, let's remember that Labile is just like Air (activates cAMP) while heat stable means stable like ground (activates cGMP)

Note that the cAMP mnemonic above is about ADP ribosylating toxins that work through cAMP activation only. There are 2 more ADB ribosylating bacteria and these are Pseudomonas and Diphtheria toxins both of work on EF-2 factor and inhibit translocation in protein synthesis.

12 Posts
ADP Ribosylation

ADP ribosylation leads to the addition of a single or multiple ribose sugars and adenine diphosphate. This is a post translational modification ( modification of an already synthesize protein). The bacteria releases an exotoxin to a particular receptor site in which a protein that is normally active is inactivated or reduces protein function/ receptor preference. Most ADP ribosylation done by bacteria are divided into 2 categories. Diphtheria/diphtheria like toxins and cholera/cholera like toxins. In order for ADP ribosylation they need NAD+ to use ADP ribose moiety done by ADP ribosyl transferase.

A. Diphtheria toxin
( High Yield)

Inactivate EF-II

1. diphtheria toxin ( C. diphtheriae)
2. exotoxin A ( P.aeruginosa)
3. cholix toxin ( V. cholera)

B.Cholera Toxin

Inactivate GS High Yield

Cholera Toxin ( V. cholera)
Heat Labile Enterotoxin ( ETEC)

Inactivate Gi (B.pertussis) High Yield

Inactivate G-actin

CD toxin ( C. difficile)
Iota toxin ( C. perfringens)
C2 toxin (C. botulinum)
VIP ( B. cereus)
SpvB ( Salmonella sp.)

Inactivate Rho or Rho like proteins

C3bot ( C. botulinum)
C3 stau I( S.aureus)
ExoS ( P.aeruginosa)
ExoT ( P. aeruginosa)
Spy A ( S. pyogenes)
C3cer ( B. cereus)

In somes questions I have encounter they test if you know toxins that have similar mechanism in inactivating same protein target ( Pseudomona, C. diphtheriae). if they belong to ADP ribosylation family regardless of target protein ( Bordetella and C. diphtheriae) and what protein do they inactivate (for example EF-II). Proteins that inactivate Rho like proteins or G-actin are very low yield.

The author of other post was right in including ETEC. You can find article in this link. What I don't agree is B. anthracis. It is said that lethal factor of B. anthracis toxin has a similar target to ADP ribosylation of B. cereus toxin but does so in a different way (metalloprotease mechanism).
1 - 9 of 9 Posts