Answers from RG members are still awaited. To my opinion, it is perhaps related to the ease with which ATP is synthesized in the living systems.

The evolution of ATP was related to energy first before life development in the earliest time at 4.2 billion years ago, while the evolution of GTP was later because it needed oxygen atom in the GTP molecule. That means the signaling function of cells was developed much later than the energy production in the mitochondria. The next useful thing to notice is that both ATP and GTP act as both energy currency and signal molecules (i.e. there are signal pathways that form cyclic AMP to carry signals, and signal pathways that form cyclic GMP, etc.). Structurally, these two molecules perform each other's functions in many different circumstances. As to why ATP ended up heavily favored as an energy currency as opposed to GTP, which is more favored in common signaling pathways, we can recognize two observations that might be factors:

1- The body needs to have some way to use energy for signaling and to use energy for other purposes. Since GTP and ATP are both presents at the same time, it makes sense to specialize one for one task and the other for the other.

2- In DNA and RNA, Adenine forms only two hydrogen bonds with the pyrimidines T and U whereas Guanine forms three with C. Therefore, if we simply had to choose which nucleotide to use for bulk energy transactions between A and G, it would make sense to choose A because there is slightly less energy required to separate it from its binding partner in structures (which would be a benefit when you want to isolate it and use it as an energy molecule).

https://www.quora.com/Why-is-ATP-the-only-energy-currency-of-the-cell-Why-not-CTP-GTP-or-UTP

There are many different molecules such as CTP, UTP, GTP, creatine phosphate, etc. are energy currency molecules. But why ATP is preferred over other energy currencies? There are different explanations to the fact:

In the reaction of hydrolysis of ATP.

ATP+H2O→ADP+Pi

Energy: -7.3 Kcal/mole.

In the above reaction, the end product ADP and Pi has no energy to form back into ATP. The reason behind this is the strong electrostatic repulsion between ADP and Pi. Charge on ADP is 3 − and on Pi is 2 −.

The second reason is the resonance stabilization of Pi. There are four possible resonating structures of inorganic phosphate molecules due to the presence of oxygen atoms. This stabilizes the phosphate molecule liberated after the hydrolysis of the ATP.

The last reason is that inorganic phosphate has a high degree of hydration (i.e. hydrophilic molecule) and hence binds to water and stabilizes itself. Thus, the hydrolysis of ATP won’t reverse back and one of the reasons why ATP is used as a high-energy currency.

Creatine Phosphate is also used as energy currency but only when energy is required rapidly as it releases high energy in very little time. ATP is comparatively slower than creatine phosphate.

https://www.quora.com/Why-is-ATP-the-only-energy-currency-of-the-cell-Why-not-CTP-GTP-or-UTP

I found these RG links, they may be useful:

https://www.researchgate.net/post/Why_did_evolution_favor_ATP_and_not_GTP_TTP_or_CTP

https://www.researchgate.net/post/Why_ATP_is_always_used_as_a_energy_source_in_almost_all_the_living_things

I agree with Dr Manal

Very interesting q.

Because hydrolysis of ATP not reversed back

Dear @Manal Hadi Kanaan Thank you so much for unraveling the mystery as to why biological systems usually use ATP as the source of energy. I appreciate your endeavor, and acknowledge your contribution.

Dear @Ali F Almehemdi and @Abdulhadi Mohamed Jumaa Thank you each one, and I appreciate and endorse your individual contribution.

Interesting question. I do agree with Manal H. K.

The evolution of ATP was related to energy first before life development in the earliest time at 4.2 billion years ago, while the evolution of GTP was later because it needed oxygen atom in the GTP molecule (remember, the oxygen level in the atmosphere was very low at that earlier time!).

Dear @Kamal M Alsaad You have shared the same knowledge which was posted earlier by @Manal Hadi Kanaan on this thread. However, I appreciate your endorsement of earlier opinion. Thank you 😊

Due to its structure and cell machinery.

GTP is structurally very similar to ATP. GTPases are used more to initiate cellular signalling pathways. It is sometimes used as an energy source. This is a good example of an alternative energy carrier.

Over the years, many proteins have specialised with a specific shape, and this chance is the primary reason behind ATP over GTP. In other words, the choice of ATP over GTP is primarily down to cellular preference of molecular shape. One of them had to emerge as being more widely used, and it was ATP that 'won'.

Very interesting question and also I liked the response. Noting that GTP is used as energy source in translation, and GTP came later in evolutionary time, the question raises another question: what was the energy molecule used for protein synthesis in those time when GTP was not there?

If we assume that ATP was still used for early translation process and later replaced by GTP, why so only for translation?

Could it be that there might have be an old, yet known, energy molecule that could have been used before GTP for translation.

I appreciate you all for the interesting discussion.

Dear @Bashir Ahmad I agree with your views. I think the use of ATP as the energy source might be related to the ease with which it is synthesized, and acts as carrier of energy in the biological system. Thank you for your contribution.

Dear @Tesfaye Sisay Tessema I appreciate your rational approach and insight towards finding the solution to the question asked on this thread. Thank you for your interest and contribution😊

ATP is commonly referred to as the "energy currency" of the cell, as it provides readily releasable energy in the bond between the second and third phosphate groups. In addition to providing energy, the breakdown of ATP through hydrolysis serves a broad range of cell functions, such as Intracellular Signaling, DNA/RNA synthesis, Purinergic Signaling, Neurotransmission, Muscle Contraction, and so on.

https://www.ncbi.nlm.nih.gov/books/NBK553175/