Role of thiamine triphosphate and adenosine thiamine triphosphate in Escherichia coli

Thiamine triphosphate (ThTP) is found in all organisms studied from bacteria to mammals. In E. coli, ThTP is accumulated as a result of amino acid starvation in the presence of a suitable carbon source such as glucose, pyruvate and lactate. On the other hand, adenosine thiamine triphosphate (AThTP), that was recently discovered in E. coli, accumulates in the absence of a carbon source.
While AThTP is synthesized in E. coli according to the reaction ThDP + ADP (ATP) ↔ AThTP + Pi (PPi) by a soluble high molecular mass nucleotidyl transferase, the mechanism of synthesis of ThTP remains unknown. Though both bacterial and mammalian adenylate kinases are able to catalyze ThTP synthesis at a very low rate in vitro, this reaction is not responsible for ThTP synthesis in vivo.
AThTP is synthesized in E. coli incubated in minimal medium devoid of any carbon source. The addition of glucose leads to the immediate disappearance of AThTP and the appearance of ThTP. ThTP production is strongly impaired in the presence of protonophores, even when a high intracellular concentration of ATP is maintained through glycolysis. Our results suggest that ThTP accumulation requires a high protonmotive force rather than a high intracellular ATP concentration. On the other hand, AThTP is synthesized under conditions of limited energy availability, either in the absence of a carbon source or in the presence of a carbon source and metabolic inhibitors or uncouplers. Interestingly, ThTP and AThTP never accumulate simultaneously in high amounts. Our results suggest that in E. coli both compounds might therefore act as specific “alarmones”, responding to different conditions of cellular stress.