Alexander F Makarchikov

Thiamine triphosphate and thiamine triphosphatase activities: from bacteria to mammals

AbstractIn most organisms, the main form of thiamine is the coenzyme thiamine diphosphate. Thiamine triphosphate (ThTP) is also found in low amounts in most vertebrate tissues and can phosphorylate certain proteins. Here we show that ThTP exists not only in vertebrates but is present in bacteria, fungi, plants and invertebrates. Unexpectedly, we found that in Escherichia coli as well as in Arabidopsis thaliana, ThTP was synthesized only under particular circumstances such as hypoxia (E. coli) or withering (A. thaliana). In mammalian tissues, ThTP concentrations are regulated by a specific thiamine triphosphatase that we have recently characterized. This enzyme was found only in mammals. In other organisms, ThTP can be hydrolyzed by unspecific phosphohydrolases. The occurrence of ThTP from prokaryotes to mammals suggests that it may have a basic role in cell metabolism or cell signaling. A decreased content may contribute to the symptoms observed during thiamine deficiency.

Thiamine diphosphate adenylyl transferase from E. coli: functional characterization of the enzyme synthesizing adenosine thiamine triphosphate

BackgroundWe have recently identified a new thiamine derivative, adenosine thiamine triphosphate (AThTP), in E. coli. In intact bacteria, this nucleotide is synthesized only in the absence of a metabolizable carbon source and quickly disappears as soon as the cells receive a carbon source such as glucose. Thus, we hypothesized that AThTP may be a signal produced in response to carbon starvation.ResultsHere we show that, in bacterial extracts, the biosynthesis of AThTP is carried out from thiamine diphosphate (ThDP) and ADP or ATP by a soluble high molecular mass nucleotidyl transferase. We partially purified this enzyme and characterized some of its functional properties. The enzyme activity had an absolute requirement for divalent metal ions, such as Mn2+ or Mg2+, as well as for a heat-stable soluble activator present in bacterial extracts. The enzyme has a pH optimum of 6.5–7.0 and a high Km for ThDP (5 mM), suggesting that, in vivo, the rate of AThTP synthesis is proportional to the free ThDP concentration. When ADP was used as the variable substrate at a fixed ThDP concentration, a sigmoid curve was obtained, with a Hill coefficient of 2.1 and an S0.5 value of 0.08 mM. The specificity of the AThTP synthesizing enzyme with respect to nucleotide substrate is restricted to ATP/ADP, and only ThDP can serve as the second substrate of the reaction. We tentatively named this enzyme ThDP adenylyl transferase (EC 2.7.7.65).ConclusionThis is the first demonstration of an enzyme activity transferring a nucleotidyl group on thiamine diphosphate to produce AThTP. The existence of a mechanism for the enzymatic synthesis of this compound is in agreement with the hypothesis of a non-cofactor role for thiamine derivatives in living cells.

Adenylate kinase 1 knockout mice have normal thiamine triphosphate levels

Thiamine triphosphate (ThTP) is found at low concentrations in most animal tissues and it may act as a phosphate donor for the phosphorylation of proteins, suggesting a potential role in cell signaling. Two mechanisms have been proposed for the enzymatic synthesis of ThTP. A thiamine diphosphate (ThDP) kinase (ThDP+ATP if ThTP+ADP) has been purified from brewers yeast and shown to exist in rat liver. However, other data suggest that, at least in skeletal muscle, adenylate kinase 1 (AK1) is responsible for ThTP synthesis. In this study, we show that AK1 knockout mice have normal ThTP levels in skeletal muscle, heart, brain, liver and kidney, demonstrating that AK1 is not responsible for ThTP synthesis in those tissues. We predict that the high ThTP content of particular tissues like the Electrophorus electricus electric organ, or pig and chicken skeletal muscle is more tightly correlated with high ThDP kinase activity or low soluble ThTPase activity than with non-stringent substrate specificity and high activity of adenylate kinase.

Adenylate Kinase-Independent Thiamine Triphosphate Accumulation under Severe Energy Stress in Escherichia Coli

BackgroundThiamine triphosphate (ThTP) exists in most organisms and might play a role in cellular stress responses. In E. coli, ThTP is accumulated in response to amino acid starvation but the mechanism of its synthesis is still a matter of controversy. It has been suggested that ThTP is synthesized by an ATP-dependent specific thiamine diphosphate kinase. However, it is also known that vertebrate adenylate kinase 1 catalyzes ThTP synthesis at a very low rate and it has been postulated that this enzyme is responsible for ThTP synthesis in vivo.ResultsHere we show that bacterial, as vertebrate adenylate kinases are able to catalyze ThTP synthesis, but at a rate more than 106-fold lower than ATP synthesis. This activity is too low to explain the high rate of ThTP accumulation observed in E. coli during amino acid starvation. Moreover, bacteria from the heat-sensitive CV2 strain accumulate high amounts of ThTP (>50% of total thiamine) at 37°C despite complete inactivation of adenylate kinase and a subsequent drop in cellular ATP.ConclusionThese results clearly demonstrate that adenylate kinase is not responsible for ThTP synthesis in vivo. Furthermore, they show that E. coli accumulate large amounts of ThTP under severe energy stress when ATP levels are very low, an observation not in favor of an ATP-dependent mechanisms for ThTP synthesis.

Neuronal localization of the 25-kDa specific thiamine triphosphatase in rodent brain.

Thiamine triphosphate (ThTP) is found in small amounts in most organisms from bacteria to mammals, but little is known about its physiological role. In vertebrate tissues, ThTP may act as a phosphate donor for the phosphorylation of certain proteins; this may be part of a new signal transduction pathway. We have recently characterized a highly specific 25-kDa thiamine triphosphatase (ThTPase) that is expressed in most mammalian tissues. The role of this enzyme may be the control of intracellular concentrations of ThTP. As the latter has been considered to be a neuroactive form of thiamine, we have studied the distribution of ThTPase mRNA and protein in rodent brain using in situ hybridization and immunohistochemistry. With both methods, we found the strongest staining in hippocampal pyramidal neurons, as well as cerebellar granule cells and Purkinje cells. Some interneurons were also labeled and many ThTPase mRNA-positive and immunoreactive cells were distributed throughout cerebral cortical gray matter and the thalamus. White matter was not significantly labeled. ThTPase immunoreactivity seems to be located mainly in the cytoplasm of neuronal perikarya. Immunocytochemical data using dissociated cultured cells from hippocampal and cerebellum showed that the staining was more intense in neurons than in astrocytes. The protein was rather uniformly located in the perikarya and dendrites, suggesting that ThTP and ThTPase may play a general role in neuronal metabolism rather than a specific role in excitability. There was no apparent correlation between ThTPase expression and selective vulnerability of certain brain regions to thiamine deficiency.