Dihydroxyacetone phosphate signals glucose availability to mTORC1.

The mechanistic target of rapamycin complex 1 (mTORC1) kinase regulates cell growth by setting the balance between anabolic and catabolic processes. To be active, mTORC1 requires the environmental presence of amino acids and glucose. While a mechanistic understanding of amino acid sensing by mTORC1 is emerging, how glucose activates mTORC1 remains mysterious. Here, we used metabolically engineered human cells lacking the canonical energy sensor AMP-activated protein kinase to identify glucose-derived metabolites required to activate mTORC1 independent of energetic stress. We show that mTORC1 senses a metabolite downstream of the aldolase and upstream of the GAPDH-catalysed steps of glycolysis and pinpoint dihydroxyacetone phosphate (DHAP) as the key molecule. In cells expressing a triose kinase, the synthesis of DHAP from DHA is sufficient to activate mTORC1 even in the absence of glucose. DHAP is a precursor for lipid synthesis, a process under the control of mTORC1, which provides a potential rationale for the sensing of DHAP by mTORC1.

Gram scale synthesis of 3-fluoro-1-hydroxyacetone phosphate: a novel donor substrate in rabbit muscle aldolase-catalyzed aldol reactions.

An efficient gram scale synthesis of 3-fluoro-1-hydroxyacetone phosphate (FHAP) has been developed. As a close analog to dihydroxyacetone phosphate, FHAP was used as a novel donor substrate for rabbit muscle aldolase catalyzed reactions. The different binding affinities of the gem-diol and keto form of FHAP were studied by (19)F-NMR.

Cloning and overexpression in Escherichia coli of the gene encoding dihydroxyacetone kinase isoenzyme I from Schizosaccharomyces pombe, and its application to dihydroxyacetone phosphate production.

The gene dak1 encoding a dihydroxyacetone kinase (DHAK) isoenzyme I, one of two isoenzymes in the Schizosaccharomyces pombe IFO 0354 strain, was cloned and sequenced. The dak1 gene comprises 1743 bp and encodes a protein of 62,245 Da. The deduced amino acid sequence showed a similarity to a putative DHAK of Saccharomyces cerevisiae and DHAK of Citrobacter freundii. The dak1 gene was expressed at a high level in Escherichia coli, and the recombinant enzyme was purified to homogeneity and characterized. The acetone powder of recombinant E. coli cells was used to produce dihydroxyacetone phosphate.

The dihydroxyacetonephosphate pathway for biosynthesis of ether lipids in Leishmania mexicana promastigotes.

Biosynthetic studies using both [14C]- and [32P]-labelled substrates and a cell-free system to synthesise 1-O-alkyl moieties in glycerolipids, have shown that the three initial steps in ether-lipid biosynthesis in Leishmania mexicana promastigotes resemble those described for mammals and are associated with glycosomes. Purified glycosomes were able to sequentially synthesise the first intermediates of the ether-lipid biosynthetic pathway [acyl-dihydroxyacetonephosphate (DHAP), alkyl-DHAP and acyl/alkyl-glycerol-3-phosphate (G3P)] when incubated in the presence of radiolabelled DHAP, palmitoyl-CoA, hexadecanol and NADPH. However, when glycosomes were incubated under the same conditions in the presence of radiolabelled G3P, a rapid synthesis of acyl-G3P and phosphatidic acid was observed without any formation of alkyl-G3P, suggesting that the enzyme alkyl-synthase recognises only acyl-DHAP as substrate. Both the DHAP acyltransferase (DHAP-AT) and alkyl-DHAP synthase activities were located inside glycosomes whereas the alkyl/acyl-DHAP oxidoreductase activity was associated with the cytoplasmic face of the glycosomal membrane. The G3P acyltransferase (G3P-AT) and lyso-phosphatidic acid acyltransferase activities were not found inside glycosomes. The results suggest that the DHAP-AT and G3P-AT activities are catalysed by two distinct enzymes associated with different sub-cellular compartments.

Biosynthesis of glycerolipid precursors in rat liver peroxisomes and their transport and conversion to phosphatidate in the endoplasmic reticulum.

The transport of glycerolipid intermediates, viz. palmitoyl dihydroxyacetone phosphate (DHAP) and lysophosphatidate from peroxisomes and their conversion to phosphatidate in endoplasmic reticulum (microsomes) were studied in cell-free systems. The lipids were biosynthesized from [32P]DHAP, palmitoyl-CoA, and freshly made rat liver peroxisomes and microsomes in the presence or absence of Mg2+, NADPH, and bovine serum albumin (BSA). After incubation, the soluble fraction and the membranes were separated, and the distribution of radioactive lipids in these fractions were determined. The results showed that palmitoyl-DHAP and lysophosphatidate were recovered in the supernatant when BSA was present or when BSA was absent, but Mg2+ was removed after incubation by chelation with EDTA (or ATP). At low optimum palmitoyl-CoA concentration or when palmitoyl-CoA was generated in peroxisomes, and in the absence of BSA, the biosynthesized keto ether and ester lipids and lysophosphatidate were similarly present in the supernatant. Phosphatidate, however, was always localized in the membranes. Further fractionation showed that phosphatidate was associated with the microsomes. The critical micellar concentrations of palmitoyl-DHAP and 1-palmitoyl-rac-glycerol 3-phosphate, under the incubation conditions used, were determined to be 58 and 70 microM, respectively. These results suggest that at physiological concentrations the biosynthesized lysolipids are water soluble, and therefore, a carrier protein is unnecessary for their transport. These lipids freely diffuse from peroxisomes to endoplasmic reticulum where they are converted to membrane-bound phosphatidate.

Hydrogen exchange in the formation of dihydroxyacetone phosphate from acyl dihydroxyacetone phosphate in O-alkyl lipid synthesis in Ehrlich ascites tumor cell microsomes.

We have previously presented evidence that acyl dihydroxyacetone phosphate is converted to O-alkyl dihydroxyacetone phosphate via an endiol intermediate which then accepts a fatty alcohol to form O-alkyl dihydroxyacetone phosphate. We have further proposed that, in the absence of fatty alcohol, the endiol derivative of acyl dihydroxyacetone phosphate reacts with water to form dihydroxyacetone phosphate. In support of this hypothesis, we have shown, in an O-alkyl generating system, that the amount of hydrogen released from acyl dihydroxyacetone phosphate in the formation of the endiol is greater than the amount of hydrogen lost from the total lipid present at the end of incubation. The discrepancy is greater in the absence of added hexadecanol. The balance of the hydrogen loss can be accounted for by the formation of a non-lipid substance which was identified as dihydroxyacetone phosphate.

Phosphorylation of glycerol and dihydroxyacetone in Acetobacter xylinum and its possible regulatory role.

Extracts of Acetobacter xylinum catalyze the phosphorylation of glycerol and dihydroxyacetone (DHA) by adenosine 5'-triphosphate (ATP) to form, respectively, L-alpha-glycerophosphate and DHA phosphate. The ability to promote phosphorylation of glycerol and DHA was higher in glycerol-grown cells than in glucose- or succinate-grown cells. The activity of glycerol kinase in extracts is compatible with the overall rate of glycerol oxidation in vivo. The glycerol-DHA kinase has been purified 210-fold from extracts, and its molecular weight was determined to be 50,000 by gel filtration. The glycerol kinase to DHA kinase activity ratio remained essentially constant at 1.6 at all stages of purification. The optimal pH for both reactions was 8.4 to 9.2. Reaction rates with the purified enzyme were hyperbolic functions of glycerol, DHA, and ATP. The Km for glycerol is 0.5 mM and that for DHA is 5 mM; both are independent of the ATP concentration. The Km for ATP in both kinase reactions is 0.5 mM and is independent of glycerol and DHA concentrations. Glycerol and DHA are competitive substrates with Ki values equal to their respective Km values as substrates. D-Glyceraldehyde and l-Glyceraldehyde were not phosphorylated and did not inhibit the enzyme. Among the nucleotide triphosphates tested, only ATP was active as the phosphoryl group donor. Fructose diphosphate (FDP) inhibited both kinase activities competitively with respect to ATP (Ki= 0.02 mM) and noncompetitively with respect to glycerol and DHA. Adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP) inhibited both enzymic activities competitively with respect to ATP (Ki (ADP) = 0.4 mM; Ki (AMP) =0.25 mM). A. xylinum cells with a high FDP content did not grow on glycerol. Depletion of cellular FDP by starvation enabled rapid growth on glycerol. It is concluded that a single enzyme from A. xylinum is responsible for the phosphorylation of both glycerol and DHA. This as well as the sensitivity of the enzyme to inhibition by FDP and AMP suggest that it has a regulatory role in glycerol metabolism.