ADP-Ribosylation by Bacterial Toxins

[MudPhud20XX]

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Alright, so Kaplan explains that toxins from both Vibrio cholera and ETEC ADP-ribosylates Gs alpha and lead to increased cAMP. On the other hand, toxin from Bordetella pertussis ADP-ribosylates Gi aplpha reducing its responsiveness to the receptor, thus increasing cAMP.

I find these two different outcome contradicting. I don't want to get bogged down by little detail and I guess they are all different toxins, so they will behave differently.

But if anyone can give me some explanation why the prior two toxins would help Gs alpha while the toxin from B. pertussis would do the opposite for Gi alpha, I would really appreciate it.

Many thanks in advance.

 

[ulikedaggers]

Alright, so Kaplan explains that toxins from both Vibrio cholera and ETEC ADP-ribosylates Gs alpha and lead to increased cAMP. On the other hand, toxin from Bordetella pertussis ADP-ribosylates Gi aplpha reducing its responsiveness to the receptor, thus increasing cAMP.

I find these two different outcome contradicting. I don't want to get bogged down by little detail and I guess they are all different toxins, so they will behave differently.

But if anyone can give me some explanation why the prior two toxins would help Gs alpha while the toxin from B. pertussis would do the opposite for Gi alpha, I would really appreciate it.

Many thanks in advance.

When Cholera binds to the G protein it inhibits the GTP -> GDP step necessary for inactivation. When Pertussis binds it causes dissociation of Gi from the a and b subunits of the g-protein thereby preventing Gi from being activated, which means preventing adenylate cyclase from being inhibited.

 

[improbable]

When Cholera binds to the G protein it inhibits the GTP -> GDP step necessary for inactivation. When Pertussis binds it causes dissociation of Gi from the a and b subunits of the g-protein thereby preventing Gi from being activated, which means preventing adenylate cyclase from being inhibited.

+1

Cholera activates the activator, while pertussis inhibits the inhibitor. Double negative equals positive.

 

[MudPhud20XX]

Got it! Thanks so much!

 

[Brucelaa67]

Is it as a result of 'un-coupling' of G protein from its receptor?