Structural Determinants of Specificity and Catalytic Mechanism in mammalian 25-kDa Thiamine Triphosphatase

in Biochimica et Biophysica Acta - General Subjects (in press)

Background: Thiamine triphosphate (ThTP) is present in most organisms and might be involved in intracellular signaling. In mammalian cells, the cytosolic ThTP level is controlled by a specific thiamine ... [more ▼]

Background: Thiamine triphosphate (ThTP) is present in most organisms and might be involved in intracellular signaling. In mammalian cells, the cytosolic ThTP level is controlled by a specific thiamine triphosphatase (ThTPase), belonging to the CYTH superfamily of proteins. CYTH proteins are present in all superkingdoms of life and act on various triphosphorylated substrates. Methods: Using crystallography, mass spectrometry and mutational analysis, we identified the key structural determinants of the high specificity and catalytic efficiency of mammalian ThTPase. Results: Triphosphate binding requires three conserved arginines while the catalytic mechanism relies on an unusual lysine-tyrosine dyad. By docking of the ThTP molecule in the active site, we found that Trp-53 should interact with the thiazole part of the substrate molecule, thus playing a key role in substrate recognition and specificity. Sea anemone and zebrafish CYTH proteins, which retain the corresponding Trp residue, are also specific ThTPases. Surprisingly, the whole chromosome region containing the ThTPase gene is lost in birds. Conclusion: The specificity for ThTP is linked to a stacking interaction between the thiazole heterocycle of thiamine and a tryptophan residue. The latter likely plays a key role in the secondary acquisition of ThTPase activity in early metazoan CYTH enzymes, in the lineage leading from cnidarians to mammals. General significance: We show that ThTPase activity is not restricted to mammals as previously thought but is an acquisition of early metazoans. This, and the identification of critically important residues, allows us to draw an evolutionary perspective of the CYTH family of proteins. [less ▲]

An alternative role of FoF1-ATP synthase in Escherichia coli: synthesis of thiamine triphosphate

in Scientific Reports (2013), 3(1071),

In E. coli, thiamine triphosphate (ThTP), a putative signaling molecule, transiently accumulates in response to amino acid starvation. This accumulation requires the presence of an energy substrate ... [more ▼]

In E. coli, thiamine triphosphate (ThTP), a putative signaling molecule, transiently accumulates in response to amino acid starvation. This accumulation requires the presence of an energy substrate yielding pyruvate. Here we show that in intact bacteria ThTP is synthesized from free thiamine diphosphate (ThDP) and Pi, the reaction being energized by the proton-motive force (Dp) generated by the respiratory chain. ThTP production is suppressed in strains carrying mutations in F1 or a deletion of the atp operon. Transformation with a plasmid encoding the whole atp operon fully restored ThTP production, highlighting the requirement for FoF1-ATP synthase in ThTP synthesis. Our results show that, under specific conditions of nutritional downshift, FoF1-ATP synthase catalyzes the synthesis of ThTP, rather than ATP, through a highly regulated process requiring pyruvate oxidation. Moreover, this chemiosmotic mechanism for ThTP production is conserved from E. coli to mammalian brain mitochondria. [less ▲]

Molecular evolution of the CYTH superfamily of proteins

in FEBS Journal (2012), 279(Suppl. s1), 438

Molecular evolution of the CYTH superfamily of proteins L. Bettendorff, D. Delvaux, G. Kohn, P. Wins, B. Lakaye GIGA-Neurosciences, University of Liège, Belgium The CYTH superfamily of proteins was named ... [more ▼]

Molecular evolution of the CYTH superfamily of proteins L. Bettendorff, D. Delvaux, G. Kohn, P. Wins, B. Lakaye GIGA-Neurosciences, University of Liège, Belgium The CYTH superfamily of proteins was named after the two founding members, the CYaB adenylyl cyclase from Aeromonas hydrophila and the human 25-kDa THiamine triphosphatase (ThTPase). Members of this superfamily of proteins exist in all organisms including bacteria, archaea, plants and animals (except in birds) and can be traced back to the Last Universal Common Ancestor. They are characterized by a consensus sequence including several charged residues involved in divalent cation and triphosphate binding. Indeed, all members of the CYTH family that are characterized act on triphosphate derivatives and require at least one divalent cation for catalysis. The Nitrosomonas europaea (1) and E.coli CYTH proteins are specific inorganic triphosphatases. We propose that inorganic triphosphate (PPPi), the most simple triphosphate compound that can be imagined, is the primitive substrate of CYTH proteins. Other enzyme activities such as adenylate cyclase (in A. hydrophila), mRNA triphosphatase (in fungi and protozoans) and ThTPase (in metazoans) activities are secondary acquisitions. We show that ThTPase activity is not limited to mammals, but Sea anemone and Zebrafish CYTH proteins are already specific ThTPases and the acquisition of this enzyme activity is linked to the presence of a Trp (W53 in mammalian ThTPases) residue involved in the binding of the thiazole heterocycle of the thiamine molecule. The importance of W53 for the specificity of mammalian ThTPases is confirmed by site-directed mutagenesis. Furthermore, we propose a conserved catalytic mechanism between inorganic triphosphatases and ThTPases, based on a catalytic dyad comprising a Lys and a Tyr residue, explaining the alkaline pH optimum of CYTH proteins. (1) Delvaux et al. J. Biol. Chem 286 (2011) 34023-35 [less ▲]

A specific inorganic triphosphatase from Nitrosomonas europaea: structure and catalytic mechanism

in Journal of Biological Chemistry (2011), 286

The CYTH superfamily of proteins is named after its two founding members, the CyaB adenylyl cyclase from Aeromonas hydrophila and the human 25-kDa thiamine triphosphatase. Because these proteins often ... [more ▼]

The CYTH superfamily of proteins is named after its two founding members, the CyaB adenylyl cyclase from Aeromonas hydrophila and the human 25-kDa thiamine triphosphatase. Because these proteins often form a closed β-barrel, they are also referred to as “Triphosphate Tunnel Metalloenzymes” (TTM). Functionally, they are characterized by their ability to bind triphosphorylated substrates and divalent metal ions. These proteins exist in most organisms and catalyze different reactions, depending on their origin. Here we investigate structural and catalytic properties of the recombinant TTM protein from Nitrosomonas europaea (NeuTTM), a 19-kDa protein. Crystallographic data show that it crystallizes as a dimer and that, in contrast to other TTM proteins, it has an open β-barrel structure. We demonstrate that NeuTTM is a highly specific inorganic triphosphatase, hydrolyzing tripolyphosphate (PPPi) with high catalytic efficiency in the presence of Mg2+. These data are supported by native mass spectrometry analysis showing that the enzyme binds PPPi (and Mg-PPPi) with high affinity (Kd < 1.5 μM), while it has a low affinity for ATP or thiamine triphosphate. In contrast to Aeromonas and Yersinia CyaB proteins, NeuTTM has no adenylyl cyclase activity, but it shares several properties with other enzymes of the CYTH superfamily, e.g. heat-stability, alkaline pH optimum and inhibition by Ca2+ and Zn2+ ions. We suggest a catalytic mechanism involving a catalytic dyad formed by K52 and Y28. The present data provide the first characterization of a new type of phosphohydrolase (unrelated to pyrophosphatases or exopolyphosphatases), able to hydrolyze inorganic triphosphate with high specificity. [less ▲]

Adenosine thiamine triphosphate accumulates in Escherichia coli cells in response to specific conditions of metabolic stress

in BMC Microbiology (2010), 10

Thiaminylated adenine nucleotides — chemical synthesis, structural characterization and natural occurrence

in FEBS Journal (2009), 276(12), 32563268

Thiamine and its three phosphorylated derivatives (mono-, di- and triphosphate) occur naturally in most cells. Recently, we reported the presence of a fourth thiamine derivative, adenosine thiamine ... [more ▼]

Thiamine and its three phosphorylated derivatives (mono-, di- and triphosphate) occur naturally in most cells. Recently, we reported the presence of a fourth thiamine derivative, adenosine thiamine triphosphate (AThTP), produced in E. coli in response to carbon starvation. Here, we show that the chemical synthesis of AThTP leads to another new compound, adenosine thiamine diphosphate (thiaminylated ADP, AThDP), as a side product. The structure of both compounds was confirmed by mass spectrometry and 1H-, 13C- and 31P-NMR and some of their chemical properties were determined. Our results show an upfield shifting of the C-2 proton of the thiazolium ring in adenosine thiamine derivatives compared to the conventional thiamine phosphate derivatives. This modification of the electronic environment of the C-2 proton might be explained by a through-space interaction with the adenosine moiety, suggesting an U-shaped folding of adenosine thiamine derivatives. Such a structure where the C-2 proton is embedded in a closed conformation can be located using molecular modeling as an energy minimum. In E. coli, AThTP may account for 15% of total thiamine under energy stress. It is less abundant in eukaryotic organisms, but is consistently found in mammalian tissues and in some cell lines. Using a HPLC method, we show for the first time that AThDP may also occur in small amounts in E. coli and in vertebrate liver. The discovery of two natural thiamine adenine compounds further highlights the complexity and diversity of thiamine biochemistry, which is not restricted to the cofactor role of thiamine diphosphate. [less ▲]

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

in BMC Microbiology (2008), 8

BACKGROUND: Thiamine 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 ... [more ▼]

BACKGROUND: Thiamine 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. RESULTS: Here 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 degrees C despite complete inactivation of adenylate kinase and a subsequent drop in cellular ATP. CONCLUSION: These 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. [less ▲]

Pig tissues express a catalytically inefficient 25-kDa thiamine triphosphatase: Insight in the catalytic mechanisms of this enzyme

in Biochimica et Biophysica Acta - General Subjects (2005), 1725(1), 93-102

Thiamine triphosphate (ThTP) is found in most organisms and may be an intracellular signal molecule produced in response to stress. We have recently cloned the cDNA coding for a highly specific mammalian ... [more ▼]

Thiamine triphosphate (ThTP) is found in most organisms and may be an intracellular signal molecule produced in response to stress. We have recently cloned the cDNA coding for a highly specific mammalian 25-kDa thiamine triphosphatase. The enzyme was active in all mammalian species studied except pig, although the corresponding mRNA was present. In order to determine whether the very low ThTPase activity in pig tissues is due to the absence of the protein or to a lack of catalytic efficiency, we expressed human and pig ThTPase in E. coli as GST fusion proteins. The purified recombinant pig GST-ThTPase was found to be 2-3 orders of magnitude less active than human GST-ThTPase. Using site-directed mutagenesis, we show that, in particular, the change of Glu85 to lysine is responsible for decreased solubility and catalytic activity of the pig enzyme. Immunohistochemical studies revealed a distribution of the protein in pig brain very similar to the one reported in rodent brain. Thus, our results suggest that a 25-kDa protein homologous to hThTPase but practically devoid of enzyme activity is expressed in pig tissues. This raises the possibility that this protein may play a physiological role other than ThTP hydrolysis. [less ▲]

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

in Neuroscience (2004), 125(4), 833-840

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 ... [more ▼]

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. (C) 2004 IBRO. Published by Elsevier Ltd. All rights reserved. [less ▲]

Human recombinant thiamine triphosphatase: purification, secondary structure and catalytic properties

in International Journal of Biochemistry & Cell Biology (2004), 36(7), 1348-1364

Thiamine triphosphate (ThTP) is found in most living organisms and it may act as a phosphate donor for protein phosphorylation. We have recently cloned the cDNA coding for a highly specific mammalian 25 ... [more ▼]

Thiamine triphosphate (ThTP) is found in most living organisms and it may act as a phosphate donor for protein phosphorylation. We have recently cloned the cDNA coding for a highly specific mammalian 25 kDa thiamine triphosphatase (ThTPase; EC 3.6.1.28). As the enzyme has a high catalytic efficiency and no sequence homology with known phosphohydrolases, it was worth investigating its structure and catalytic properties. For this purpose, we expressed the untagged recombinant human ThTPase (hThTPase) in E. coli, produced the protein on a large scale and purified it to homogeneity. Its kinetic properties were similar to those of the genuine human enzyme, indicating that the recombinant hThTPase is completely functional. Mg2+ ions were required for activity and Ca2+ inhibited the enzyme by competition with Mg2+. With ATP as substrate, the catalytic efficiency was 10(-4)-fold lower than with ThTP, confirming the nearly absolute specificity of the 25 kDa ThTPase for ThTP. The activity was maximum at pH 8.5 and very low at pH 6.0. Zn2+ ions were inhibitory at micromolar concentrations at pH 8.0 but activated at pH 6.0. Kinetic analysis suggests an activator site for Mg2+ and a separate regulatory site for Zn2+. The effects of group-specific reagents such as Woodward's reagent K and diethylpyrocarbonate suggest that at least one carboxyl group in the active site is essential for catalysis, while a positively charged amino group may be involved in substrate binding. The secondary structure of the enzyme, as determined by Fourier-transform infrared spectroscopy, was predominantly beta-sheet and alpha-helix. [less ▲]