Thiamine triphosphate synthesis in Escherichia coli requires FoF1-ATPase

Exponentially growing E. coli cells contain high amounts of thiamine diphosphate (ThDP), a well-known cofactor, but only ~20% is bound to apoenzymes. We showed that the abundant free ThDP is the precursor for two triphosphorylated derivatives, thiamine triphosphate (ThTP) and the newly discovered adenosine thiamine triphosphate (AThTP). Both compounds are produced under different conditions of stress. ThTP transiently accumulates in response to amino acid starvation, but, in contrast to AThTP, its synthesis requires the presence of a carbon source yielding pyruvate. Under such conditions, the amount of cellular ThTP may reach up to 20–60% of total thiamine, while it is generally a minor compound (0.1 to 1% of total thiamine). The biological role of ThTP remains uncertain until now, though in E. coli, it seems to be required for rapid adaptation to amino acid starvation. ThTP accumulation requires inorganic phosphate and is inhibited by anoxia and cyanide. It is also blocked by low concentrations of the protonophore CCCP and is inhibited by low concentrations of DCCD, an inhibitor of FoF1-ATP synthase. These results suggest that ThTP is synthesized by a mechanism similar to oxidative phosphorylation, i. e. the reaction ThDP + Pi  ThTP catalyzed by FoF1-ATP synthase and energized by respiration. This hypothesis is supported by the finding that E. coli with FoF1-ATP synthase mutated in various subunits are unable to synthesize ThTP in minimal medium in response to glucose exposure. Moreover, a strain in which the atp operon was deleted is unable to synthesize ThTP, but transformation with a plasmid encoding the atp operon totally restores this capacity. We recently demonstrated a similar chemiosmotic mechanism for ThTP synthesis in rat brain mitochondria suggesting a conserved mechanism for ThTP synthesis between bacteria and mammals.