Why is GTP used in cell signalling rather than ATP?

[robertfw]

G proteins such as Ras use GTP in cell signalling. Is there a reason why they don't use ATP instead? Can anyone throw any light on this? Thanks very much indeed for taking the time to respond.

[Prolific]

Might be wrong but I read something a while ago which said that it was probably just evolutionary chance that ATP ended up being the principal energy coenzyme not another phosphorylated nucleotide like GTP or UTP. As far as I know the free energy that can be released from the bonds is basically the same. ATP and GTP synthesis are pretty interlinked though. For example in purine nucleotide synthesis, one molecule of ATP is needed to make a GMP and vice versa one molecule of GTP is needed to make one molecular of AMP.

Might be totally wrong about all of that since its been 18 months since I last did it and its 3:40am :S

[Le Pom]

can anyone help with this question i have to do:

draw annotated diagram(s) to describe in detail how the signalling mechanism is relayed by a ligand bound intracellular steroid receptor via Src kinase and what the resulting affects are.



..any help would be appreciated. or links or anything. i can only find parts of the answer and cannot complete a whole diagram on it.... :S


~Pamela~

[Lovejones07]

ATP is used in signalling. I know its used as an extracellular signalling molecule but im sure its involved in modulating 2o messengers as well.
Also, its the cyclic nucleotide derivative cAMP is probably the most commonly occuring 2o messenger used. (just look at olfaction etc for examples)

finding a reason why one nucleotide is used rather than another is quite an intereasting question really. Also, remember that there is more phospho nucleotides. I wonder if their slightly different chemistry defines what particular roles they have in the cell.

Sorry, thats more random musing than it is answer to your question, its a bit early.

Adam