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Diadenosine tetraphosphate (Ap4A) - an E. coli alarmone or a damage metabolite?
Dragana Despotović1, Alexander Brandis2, Alon Savidor3
1Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel.
The FEBS Journal
|May 19, 2017
Summary
Diadenosine tetraphosphate (Ap4A) was long thought to be a stress alarmone. However, research shows it is a damage metabolite, accumulating to toxic levels under stress and not triggering signaling pathways.
Area of Science:
- Metabolic regulation
- Molecular signaling
- Stress response
Background:
- Metabolism changes under stress, producing signaling molecules (alarmones) and side products (damage metabolites).
- Diadenosine tetraphosphate (Ap4A), a side product of aminoacyl-tRNA synthetases, was hypothesized to be an alarmone for heat stress.
- Despite 50 years of research, Ap4A's role in cellular signaling remains unclear.
Purpose of the Study:
- To systematically classify Ap4A as either an alarmone or a damage metabolite.
- To investigate the signaling mechanisms, if any, associated with Ap4A.
- To determine the physiological consequences of Ap4A accumulation.
Main Methods:
- Defined criteria to distinguish alarmones from damage metabolites.
- Investigated Ap4A's response to stress and its removal mechanisms.
- Assessed the effects of Ap4A concentration changes on cellular processes.
Main Results:
- No evidence was found for an Ap4A-triggered signaling cascade.
- Ap4A is constitutively and non-regulatedly removed.
- High Ap4A levels are toxic, disrupting zinc homeostasis and interfering with ATP-binding proteins.
Conclusions:
- Ap4A fulfills all criteria for a damage metabolite, not an alarmone.
- The hypothesis that Ap4A acts as a damage metabolite should be the default assumption in stress-related research.
- Further investigation into Ap4A's potential signaling roles is warranted but should consider its damage metabolite characteristics.
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