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PubMed1990

Protein phosphorylation in pancreatic islets induced by 3-phosphoglycerate and 2-phosphoglycerate.

We have shown previously that 3-phosphoglycerate, which is a glycolytic metabolite of glucose, induces protein phosphorylation in bovine and rat brain and in rat heart, kidney, liver, lung, and whole pancreas. Since glycolytic metabolism of glucose is of paramount importance in insulin release, we considered the possibility that 3-phosphoglycerate may act as a coupling factor, and we searched for evidence for the existence of 3-phosphoglycerate-dependent protein phosphorylation systems in freshly isolated normal rat pancreatic islets. Membrane and cytosol fractions were incubated with [gamma-32P]ATP and appropriate test substances and were subjected to NaDodSO4/PAGE and autoradiography. As little as 0.005 mM 3-phosphoglycerate or 2-phosphoglycerate stimulated the phosphorylation of a 65-kDa cytosol protein by as early as 0.25 min. The phosphate bond of the 65-kDa phosphoprotein was sufficiently stable to withstand dialysis; the radioactivity could not be chased out by subsequent exposure to ATP, ADP, 3-phosphoglycerate, or 2,3-bisphosphoglycerate. Moreover, cAMP, cGMP, phorbol 12-myristate 13-acetate, or calcium failed to stimulate the phosphorylation of the 65-kDa protein. Phosphoglycerate-dependent protein phosphorylation in islets may have relevance to stimulation of insulin secretion.

Bisphosphoglycerate Mutase↗
PubMed2000

Activation of the potato tuber ADP-glucose pyrophosphorylase by thioredoxin.

The potato tuber (Solanum tuberosum L.) ADP-glucose pyrophosphorylase (ADP-GlcPPase) catalyzes the first committed step in starch biosynthesis. The main type of regulation of this enzyme is allosteric, and its activity is controlled by the ratio of activator, 3-phosphoglycerate to inhibitor, P(i). It was reported (Fu, Y., Ballicora, M. A., Leykam, J. F., and Preiss, J. (1998) J. Biol. Chem. 273, 25045-25052) that the enzyme was activated by reduction of the Cys(12) disulfide linkage present in the catalytic subunits. In this study, both reduced thioredoxin f and m from spinach (Spinacia oleracea) leaves reduced and activated the enzyme at low concentrations (10 microM) of activator (3-phosphoglycerate). Fifty percent activation was at 4.5 and 8.7 microM for reduced thioredoxin f and m, respectively, and 2 orders of magnitude lower than for dithiothreitol. The activation was reversed by oxidized thioredoxin. Cys(12) is conserved in the ADP-GlcPPases from plant leaves and other tissues except for the monocot endosperm enzymes. We postulate that in photosynthetic tissues, reduction could play a role in the fine regulation of the ADP-GlcPPase mediated by the ferredoxin-thioredoxin system. This is the first time that a covalent mechanism of regulation is postulated in the synthesis of starch.

Allosteric Regulation↗
PubMed2002

Plasmin reduction by phosphoglycerate kinase is a thiol-independent process.

Phosphoglycerate kinase (PGK) is secreted by tumor cells and facilitates reduction of disulfide bond(s) in plasmin (Lay, A. J., Jiang, X.-M., Kisker, O., Flynn, E., Underwood, A., Condron, R., and Hogg, P. J. (2000) Nature 408, 869-873). The angiogenesis inhibitor, angiostatin, is cleaved from the reduced plasmin by a combination of serine- and metalloproteinases. The chemistry of protein reductants is typically mediated by a pair of closely spaced Cys residues. There are seven Cys in human PGK, and mutation of all seven to Ala did not appreciably affect plasmin reductase activity, although some of the mutations perturbed the tertiary structure of the protein. Cys-379 and Cys-380 are close to the hinge that links the N- and C-terminal domains of PGK. Alkylation/oxidation of Cys-379 and -380 by four different thiol-reactive compounds reduced plasmin reductase activity to 7--35% of control. Binding of 3-phosphoglycerate and/or MgATP to the N- and C-terminal domains of PGK, respectively, triggers a hinge bending conformational change in the enzyme. Incubation of PGK with 3-phosphoglycerate and/or MgATP ablated plasmin reductase activity, with half-maximal inhibitory effects at approximately 1 mm concentration. In summary, reduction of plasmin by PGK is a thiol-independent process, although either alkylation/oxidation of the fast-reacting Cys near the hinge or hinge bending conformational change in PGK perturbs plasmin reduction by PGK, perhaps by obstructing the interaction of plasmin with PGK or perturbing conformational changes in PGK required for plasmin reduction.

Adenosine Triphosphate↗
PubMed2003

Structure of Plasmodium falciparum triose-phosphate isomerase-2-phosphoglycerate complex at 1.1-A resolution.

Triose-phosphate isomerase, a key enzyme of the glycolytic pathway, catalyzes the isomerization of dihydroxy acetone phosphate and glyceraldehyde 3-phosphate. In this communication we report the crystal structure of Plasmodium falciparum triose-phosphate isomerase complexed to the inhibitor 2-phosphoglycerate at 1.1-A resolution. The crystallographic asymmetric unit contains a dimeric molecule. The inhibitor bound to one of the subunits in which the flexible catalytic loop 6 is in the open conformation has been cleaved into two fragments presumably due to radiation damage. The cleavage products have been tentatively identified as 2-oxoglycerate and meta-phosphate. The intact 2-phosphoglycerate bound to the active site of the other subunit has been observed in two different orientations. The active site loop in this subunit is in both open and "closed" conformations, although the open form is predominant. Concomitant with the loop closure, Phe-96, Leu-167, and residues 208-211 (YGGS) are also observed in dual conformations in the B-subunit. Detailed comparison of the active-site geometry in the present case to the Saccharomyces cerevisiae triose-phosphate isomerase-dihydroxy acetone phosphate and Leishmania mexicana triose-phosphate isomerase-phosphoglycolate complexes, which have also been determined at atomic resolution, shows that certain interactions are common to the three structures, although 2-phosphoglycerate is neither a substrate nor a transition state analogue.

Animals↗
PubMed2004

Protein stabilization by osmolytes from hyperthermophiles: effect of mannosylglycerate on the thermal unfolding of recombinant nuclease a from Staphylococcus aureus studied by picosecond time-resolved fluorescence and calorimetry.

2-O-alpha-Mannosylglycerate, a negatively charged osmolyte widely distributed among (hyper)thermophilic microorganisms, is known to provide notable protection to proteins against thermal denaturation. To study the mechanism responsible for protein stabilization, pico-second time-resolved fluorescence spectroscopy was used to characterize the thermal unfolding of a model protein, Staphylococcus aureus recombinant nuclease A (SNase), in the presence or absence of mannosylglycerate. The fluorescence decay times are signatures of the protein state, and the pre-exponential coefficients are used to evaluate the molar fractions of the folded and unfolded states. Hence, direct determination of equilibrium constants of unfolding from molar fractions was carried out. Van't Hoff plots of the equilibrium constants provided reliable thermodynamic data for SNase unfolding. Differential scanning calorimetry was used to validate this thermodynamic analysis. The presence of 0.5 m potassium mannosylglycerate caused an increase of 7 degrees C in the SNase melting temperature and a 2-fold increase in the unfolding heat capacity. Despite the considerable degree of stabilization rendered by this solute, the nature and population of protein states along unfolding were not altered in the presence of mannosylglycerate, denoting that the unfolding pathway of SNase was unaffected. The stabilization of SNase by mannosylglycerate arises from decreased unfolding entropy up to 65 degrees C and from an enthalpy increase above this temperature. In molecular terms, stabilization is interpreted as resulting from destabilization of the denatured state caused by preferential exclusion of the solute from the protein hydration shell upon unfolding, and stabilization of the native state by specific interactions. The physiological significance of charged solutes in hyperthermophiles is discussed.

Calorimetry↗
PubMed2004

Differential pattern of expression and sugar regulation of Arabidopsis thaliana ADP-glucose pyrophosphorylase-encoding genes.

ADP-glucose pyrophoshorylase (ADP-Glc PPase) catalyzes the first and limiting step in starch biosynthesis. In plants, the enzyme is composed of two types of subunits (small and large) and is allosterically regulated by 3-phosphoglycerate and phosphate. The pattern of expression and sugar regulation of the six Arabidopsis thaliana ADP-Glc PPase-encoding genes (two small subunits, ApS1 and ApS2; and four large subunits, ApL1-ApL4) has been studied. Based on mRNA expression, ApS1 is the main small subunit or catalytic isoform responsible for ADP-Glc PPase activity in all tissues of the plant. Large subunits play a regulatory role, and the data presented define a clear functional distinction among them. ApL1 is the main large subunit in source tissues, whereas ApL3 and, to a lesser extent, ApL4 are the main isoforms present in sink tissues. Thus, in source tissues, ADP-Glc PPase would be finely regulated by the 3-phosphoglycerate/phosphate ratio, whereas in sink tissues, the enzyme would be dependent on the availability of substrates for starch synthesis. Sugar regulation of ADP-Glc PPase genes is restricted to ApL3 and ApL4 in leaves. Sugar induction of ApL3 and ApL4 transcription in leaves allows the establishment of heterotetramers less sensitive to the allosteric effectors, resembling the situation in sink tissues. The results presented on the expression pattern and sugar regulation allow us to propose a gene evolution model for the Arabidopsis ADP-Glc PPase gene family.

Adenosine Diphosphate↗
PubMed2006

Molecular properties of Oep21, an ATP-regulated anion-selective solute channel from the outer chloroplast membrane.

The flux of phosphorylated carbohydrates, the major export products of chloroplasts, is regulated at the level of the inner and presumably also at the level of the outer membrane. This is achieved through modulation of the outer membrane Oep21 channel currents and tuning of its ion selectivity. Refined analysis of the Oep21 channel properties by biochemical and electrophysiological methods revealed a channel formed by eight beta-strands with a wider pore vestibule of dvest approximately 2.4 nm at the intermembrane site and a narrower filter pore of drestr approximately 1 nm. The Oep21 pore contains two high affinity sites for ATP, one located at a relative transmembrane electrical distance delta = 0.56 and the second close to the vestibule at the intermembrane site. The ATP-dependent current block and reduction in anion selectivity of the Oep21 channel is relieved by the competitive binding of phosphorylated metabolic intermediates like 3-phosphoglycerate and glycerinaldehyde 3-phosphate. Deletion of a C-terminal putative FX4K binding motif in Oep21 decreased the capability of the channel to tune its ion selectivity by about 50%, whereas current block remained unchanged.

Adenosine Triphosphate↗
PubMed2004

Respiratory acclimation in Arabidopsis thaliana leaves at low temperature.

Acclimation of 25 degrees C-grown Arabidopsis thaliana at 5 degrees C resulted in a marked increase of leaf respiration in darkness (Rd) measured at 5 degrees C. Rd was particularly high in leaves developed at 5 degrees C. Leaf respiration (non-photorespiratory intracellular decarboxylation) in the light (Rl) also increased during cold acclimation, but less so than did Rd. The ratio Rd/Pt (Pt - true photosynthesis) was higher in more acclimated or cold-developed leaves, while the ratio Rl/Pt remained unchanged. In cold-acclimated leaves, Rl did not correlate with 3-phosphoglycerate and pyruvate nor with hexose phosphate pools in the cytosol. Rl in A. thaliana leaves was probably not limited by the substrate during cold acclimation. Under the conditions tested, Rd was more sensitive to low temperature stress than Rl.

Acclimatization↗
PubMed2006

Isolation and characterization of the human D-glyceric acidemia related glycerate kinase gene GLYCTK1 and its alternatively splicing variant GLYCTK2.

Deficiency of human glycerate kinase leads to D-glycerate acidemia/D-glyceric aciduria. Through PCR cloning assisted by in silico approach, we isolated the human glycerate kinase genes--Glycerate Kinase 1 (GLYCTK1) and its alternatively splicing variant--Glycerate Kinase 2 (GLYCTK2), which might be associated with D-glycerate acidemia/D-glyceric aciduria. The locus of GLYCTK gene is mapped to 3p21. PCR amplification in seventeen human tissue cDNAs revealed that both GLYCTK1 and GLYCTK2 are expressed widely almost in all these tissues. The expression of mouse Glyctk in various tissues was demonstrated by in situ hybridization. Both GLYCTK1 and GLYCTK2 proteins are localized in cytosol, and GLYCTK2 proteins are specifically localized in mitochondria. Present results revealed the characteristic expression pattern of murine Glyctk in neural system, skeleton muscle, supporting that glycerate kinase is implicated in D-glycerate acidemia/D-glyceric aciduria.

Alternative Splicing↗
PubMed1999

A rectifying ATP-regulated solute channel in the chloroplastic outer envelope from pea.

Phosphorylated carbohydrates are the main photoassimilated export products from chloroplasts that support the energy household and metabolism of the plant cell. Channels formed by the chloroplastic outer envelope protein OEP21 selectively facilitate the translocation of triosephosphate, 3-phosphoglycerate and phosphate, central intermediates in the source-sink relationship between the chloroplast and the cytosol. The anion selectivity and asymmetric transport properties of OEP21 are modulated by the ratio between ATP and triosephosphates, 3-phosphoglycerate and phosphate in the intermembrane space. Conditions that lead to export of triosephosphate from chloroplasts, i.e. photosynthesis, result in outward-rectifying OEP21 channels, while a high ATP to triosephosphate ratio, e.g. dark metabolism, leads to inward-rectifying OEP21 channels with a less pronounced anion selectivity. We conclude that solute exchange between plastids and cytosol can already be regulated at the level of the organellar outer membrane.

Adenosine Triphosphate↗
PubMed2002

Manipulating PEPC levels in plants.

This review examines the current understanding of the structural, functional and regulatory properties of C4 and C3 forms of higher plant phosphoenolpyruvate carboxylase. The emphasis is on the interactive metabolic and post-translational controls acting on the enzyme in the physiological context of C4 photosynthesis and the anaplerotic pathway. A brief overview is given concerning the recent developments of PEPC-based genetic engineering of C3 plants with the aim of improving photosynthetic performance in normal and limiting environmental conditions. So far, in spite of achieving a considerable increase in PEPC levels, more work needs to be done with respect to the correct dosage and location before that goal is reached. Some unpublished results on the transformation of maize with a sorghum C4 PEPC cDNA are also presented. They show that it is possible to increase photosynthetic PEPC levels in this C4 plant and that the modification in enzyme content has a pleiotropic physiological impact and, notably, an improved water use efficiency when water is limited.

Biomass↗
PubMed2003

Subcellular localization of ADPglucose pyrophosphorylase in developing wheat endosperm and analysis of the properties of a plastidial isoform.

The intracellular location of ADPglucose pyrophosphorylase (AGPase) in wheat during endosperm development was investigated by analysis of the recovery of marker enzymes from amyloplast preparations. Amyloplast preparations contained 20-28% of the total endosperm activity of two plastidial marker enzymes and less than 0.8% of the total endosperm activity of two cytosolic marker enzymes. Amylo plasts prepared at various stages of development, from 8-30 d post anthesis, contained between 2% and 10% of the total AGPase activity; this implies that between 7% and 40% of the AGPase in wheat endosperm is plastidial during this period of development. Two proteins were recognized by antibodies to both the large and small subunits of wheat AGPase. The larger of the two AGPases was the major form of the enzyme in whole cell extracts, and the smaller, less abundant, form of AGPase was enriched in plastid preparations. The results are consistent with data from other graminaceous endosperms, suggesting that there are distinct plastidial and cytosolic isoforms of AGPase composed of different subunits. The plastidial isoform of AGPase from wheat endosperm is relatively insensitive to the allosteric regulators 3-phosphoglycerate and inorganic orthophos phate compared with plastidial AGPase from other species. Amyloplast AGPase showed no sensitivity to physiological concentrations of inorganic orthophosphate. 15 mM 3-phosphoglycerate caused no stimulation of the pyrophosphorolytic reaction, and only 2-fold stimulation of the ADPglucose synthesizing reaction.

Cytosol↗
PubMed1995

Primary hyperoxaluria type 2.

Most cases of primary hyperoxaluria are due to deficiency of hepatic peroxisomal alanine:glyoxylate aminotransferase [i.e. primary hyperoxaluria type 1 (PH1), McKusick 259900] and several hundred examples have been described since the original report in 1925. By contrast, primary hyperoxaluria type 2 (PH2, McKusick 260000) is very rare indeed with only 22 patients recorded since the original description in 1968. PH2 is characterized by hyperoxaluria and L-glyceric aciduria and is caused by deficiency of D-glycerate dehydrogenase/glyoxylate reductase. In comparison with PH1 much less is known about PH2 and considerable uncertainties remain about its frequency, clinical course and optimum management.

Adult↗